HIERARCHICAL ENCAPSULATION OF INSTANTIATED OBJECTS

Abstract: An application development system, optimized for authoring multimedia titles, enables users to create selectively reusable object containers by defining links among instantiated objects. The system utilizes hierarchical encapsulation to automatically isolate external dependencies of object containers created by its users, thereby facilitating reusability of object containers and the objects they contain in other container environments. Authors create two basic types of objects: elements (108-111), which are the key actors within an application, and modifiers (114-117, 119, 122, 123) which modify an element (109-110) characteristics. The object containers (elements and behaviors (118, 120) - i.e., modifier containers) created by authors spawn hierarchies of objects, including the structural hierarchy of elements (111) within elements (108), and the behavioral hierarchy (118), within an element (110), of behaviors (and other modifiers (122, 123), within behaviors (120). The system utilizes an element's dual hierarchies to make that element an environmental frame of reference to the objects it contains.

Description: 1822 PCIYUS96/044 6 ■ HIERARCHICAL ENCAPSULATION OF INSTANTIATED OBJECTS". I. BACKGROUND. A. Field of the Invention. This invention relates to application development systems generally, and in particular to systems for authoring interactive multimedia applications. B. Description of the Related Art. Since the advent of computers many decades ago, computer scientists have labored to build increasingly powerful computer hardware that is faster and cheaper to build than its predecessors. Today's computers can perform, in one second, many millions of "add," "shift," "load," "store" and other relatively simple functions. To perform tasks of any significant complexity, however, one must somehow cause computers to perform vast numbers of these simple functions in some sequence. Computer software, in its most basic form, comprises programs or sequences of instructions, each of which directs a computer to perform the function corresponding to that instruction. Yet, even as computers have become more powerful, developers of computer software continue to struggle to create complex programs without having to "reinvent the wheel" for each task they direct computers to perform. This need 1 for "reusability" permeates virtually every aspect of software development, and is driven ultimately by the end user's desire for "ease of use." 1. Reusability and the Modular Interface. Although there are many varied approaches to this basic problem of reusability, one technique remains constant — "modular programming," i.e., the "bootstrapping" of multiple simple functions into "modules" of greater and greater complexity that can be reused through higher-level "modular interfaces. " Virtually all software relies on modular programming to some extent. For example, assemblers and compilers enable programmers to bootstrap from the machine language defined by a computer's instruction set to a higher-level, more human-readable language. Similarly, operating systems perform many of the low-level support tasks commonly needed by applications software developers (e.g., file system, memory management, basic GUI routines, etc.), and then provide developers with a library of "reusable" modules. In essence, all application development systems provide to their users a language, an application programming interface ("API"), or some other form of modular interface designed to facilitate development of general purpose or highly specialized applications. Such modular interfaces provide reusability of the "hidden" functionality which implements that interface. 2. Encapsulation and the Object Interface. One of the most popular current trends designed to promote the creation of reusable software is in the field of object-oriented programming ("OOP"). There are a variety of OOP languages and application development tools on the market today (e.g. , C+ + and Kaleida Labs' "ScriptX™"), as well as a number of "pseudo-OOP" tools (e.g. , "HyperCard™" from Apple Computer and "Visual Basic™" from Microsoft) which borrow some, but not all, of the basic principles of OOP. OOP systems generally are intended to extend reusability to all portions of a computer program, not just to particular modules. This is accomplished by distributing control of the various tasks performed by a program to individual "objects" with well-defined modular interfaces. These objects typically communicate by directly calling one another's capabilities or "methods. " OOP application development systems generally require their users to define abstract "classes" of objects that define the characteristics of the objects in that class. The actual objects in the user's application are instantiated as needed at "runtime" from this class "template. " Such systems also typically include certain built-in reusable class libraries to provide the user with an initial base of functionality. The instantiated objects that perform the various tasks within the user's application are reusable in large part due to a process known as "encapsulation. " Encapsulation involves defining a class of objects with a well-defined external interface, and "hiding" widiin the objects the code and data necessary to implement that interface. In other words, the implementation of an object's interface is "encapsulated" entirely widiin the object. Thus, programmers can reuse objects in various different contexts within their application. All other objects that are aware of this interface can "reuse" this object because its external dependencies are isolated widiin its modular "object interface. " Programmers also can use a process known as "inheritance" to "specialize" or modularly extend an object's functionality by reusing some or all of that object's characteristics via its interface or class definition — i.e., the public methods and data structures that define the template for instances of that class. For example, programmers may wish to extend the base functionality of an existing class (whether created by die programmer or provided in a reusable class library) by adding a new mediod to objects in that class, or replacing (i.e., overriding) or supplementing (i.e. , overloading) an existing method. By defining a sub-class of objects that "inherit" the characteristics of the "parent" class, the programmer can reuse (as well as add to, replace or supplement) diose inherited characteristics. For example, a "car" or "bus" sub-class might inherit characteristics from a more general "vehicle" class. A car is a "kind of" vehicle, and may inherit, for example, a vehicle's color and speed properties, as well as steering and braking methods. The Need for Selective Reusability of "User Objects". Despite their facilities for reusability of objects, OOP application development systems remain difficult to use. It is far simpler for application developers to create and configure instantiated objects directly, as opposed to defining abstract classes each time they need to create a slightly different object or to model d e relationships or interaction among existing objects. This problem is exacerbated when an application developer creates and desires to reuse compound or aggregate "user objects" — i.e., a group of objects that are related in die context of a particular application, but do not necessarily share common characteristics. These "user objects," in addition to requiring extensive inter-object communication, often involve "part of" or "container" relationships that occur frequently in any modularly designed application. Inheritance and encapsulation are well-suited to model "kind of relationships to further specialize the atomic objects from which an application will be built. All modular systems require certain atomic "building blocks" which are reusable and provide sufficient performance, even if difficult to modify. To create applications of any significant complexity, however, one must combine d ese atomic objects into more complex "user objects" that interact widi one another. It is this common modular process that illustrates the significant limitations on reusability imposed by traditional OOP systems. OOP systems allow developers to "reuse" an existing class of objects by: (i) creating a class of objects that inherits from and "specializes" that existing class; (ii) creating a class of objects that encapsulates that existing class within its private (hidden) data structures and methods; or (iii) creating a distinct class of objects that communicates with (i.e., invokes methods of) that existing class of objects. Yet, in all three cases, the new class of objects is tightly coupled to, and dius highly dependent upon, die existing class of objects. Mere communication among otherwise unrelated objects provides virtually no reusability, and creates many explicit dependencies. Almough inheritance and encapsulation provide reusability of objects at various levels of complexity, a class of objects at any given level of complexity remains highly dependent upon d e particular characteristics it encapsulates or inherits from its less complex superclasses. It therefore remains. quite difficult, if not impossible, to "selectively reuse" characteristics from (and interaction among) complex "user objects" in new environments. One cannot, for example, easily "mix and match" object characteristics across class libraries and choose "some from column A and some from column B." At any given level of complexity, a developer cannot simply replace undesired characteristics of a complex object from one class library with the more desirable characteristics of another complex object from a different class library. Until such selective reusability is achieved, d e ultimate promise of OOP cannot be considered fulfilled. a. An OOP Windowing Example. Consider me following example involving simple windowing functionality, a very common application for traditional OOP systems. Imagine two independent developers ("A" and "B") creating windowing systems in a typical OOP development environment. Developer A might create a "Window" class of window objects with a name ("Window X"), a particular size (specified by a bounding rectangle), a title bar (specified by anodier bounding rectangle), a color and a beveled border. Its only functionality might be to create, destroy and draw d ese window objects, via three respective methods. To enhance the functionality of these window objects in a modular manner, Developer A might create a "Minimize" subclass that inherits from the Window class and adds a "minimize" capability. When a user clicks on the small minimize box in the upper right hand corner of the window, die minimize object transforms the window object into a small icon at the bottom of the screen,. When the user clicks on the icon, d e window is restored. This Minimize subclass would require "minimize" and "maximize" methods to perform diese functions, as well as a minimize box (specified by a bounding rectange), a minimize flag (indicating the state of the window — i.e., whether it is currently minimized), and data for a minimize icon (pattern, size, position, etc.). In addition, the Minimize subclass would overload d e create, destroy and draw memods of the Window class — i.e. , to create, destroy and draw die minimize box and/or icon as well as the window. Finally, Developer A might add additional "drag" functionality to these window objects, which would enable the user to drag the window by its title bar. This subclass could inherit all data and mediods from the Minimize subclass (which itself inherits from the Window class), and simply add a "drag" mediod. Developer B independently might take a similar approach. But, the class of Window objects created by Developer B (named Window X') might not include the beveled border. Moreover, Developer B might add a "window shade" capability that differs slightly from the minimize capability created by Developer A. When the user "double clicks" on the title bar of Window X', the Window might "roll up," showing only the title bar. Developer B might implement is capability by creating a "Window Shade" subclass diat inherits from (and overloads the mediods of) the Window class, and adds a drag method to implement this "window shade" capability. That subclass might also include a flag to track whether the window currently is "pulled up." Assume that Developers A and B distribute their respective object classes in class libraries containing the public interface (i.e. , die methods and data identified above), but not the private code and data that implements that interface. Selective reusability would allow Developer "C" to reuse all or any modular portion of the functionality created by Developers A and B, without recompiling mese classes or obtaining access to any such private code. It is true that Developer C could reuse d e Window class, the Minimize subclass or the Drag subclass, thereby reusing functionality at various levels of abstraction. But, what if Developer C wanted to reuse the window and die drag capability created by Developer A, but integrate d e window shade capability of Window X' in lieu of the minimize capability of Window X? In short, Developer C cannot easily accomplish mis task. The problem is that the private data and mediods of d e Minimize and Drag subclasses are dependent upon the public data and methods of the classes from which they inherit. The code might not even link. The Drag subclass inherits from, and thus assumes d e existence of, die Minimize class. The drag method might, for example, modify die bounding rectangle of a Minimize object to "move" that object (as well as the rest of the window) across the screen as d e user drags die window. This dependency effectively prevents Developer C from replacing the Minimize class with the Window Shade class. The drag method would attempt to modify data that no longer exists. Developer C would be forced to rewrite the Window Shade and Drag classes (potentially a significant amount of code) merely to reuse the Window class. Reusability dierefore is substantially impaired by the external (inter-class or inter-object) dependencies of a subclass on its superclass. As noted above, encapsulating diese dependencies or invoking other objects' methods widiin a class' private methods (as opposed to relying on inheritance) creates similar dependencies and perhaps even less reusability. Any system of reasonable complexity will contain many levels of these external dependencies, making selective reusability of complex "user objects" across class libraries extremely difficult, if not practically impossible. As discussed below, today's application development systems create similar external dependencies mat impair selective reusability. 4. The Lack of Selective Reusability in Multimedia Authoring Systems. Consider, for example, die field of multimedia authoring systems to which an embodiment of the present invention is directed. Aldiough ttiere exist many such systems widi almost as many different techniques, these systems all impose 8 significant limitations on the author's ability to selectively reuse complex "user objects" across different environments. Certain systems, such as Macromedia's Director,™ employ traditional metaphors with which authors are familiar and quite comfortable. Director employs a frame-based metaphor that requires authors to determine precisely which objects will be present in each frame of a sequence. This metaphor is familiar to animators, and frequently is used for constructing sequential animation sequences containing relatively little interactivity. Constructing highly interactive applications, however, is quite difficult within die confines of a frame-based environment. Even widi a scripting language included to provide greater control over the sequence in which characters appear, interactivity frequently is limited to that provided by one or more scripts within a frame. It is quite difficult to reuse any of the characteristics of a particular object, because die object is highly dependent upon its environment (i.e., die scripts of other objects that "call" it, as well as the confines of the frames in which it appears, relative to other objects). Extensive reliance on scripting to model interactivity makes it difficult to isolate an object's external dependencies within a single script, and virtually impossible to isolate such dependencies across multiple scripts. Rigorous OOP tools (such as the ScriptX™ language from Kaleida Labs and die more visually oriented Quest™ from Allen Communication) still require significant programming expertise on the part of dieir users. Despite offering extensive libraries of reusable "high-level" objects, such products remain relatively low-level development tools — i.e., OOP programming languages (or perhaps visual programming languages), as opposed to audioring tools. As noted above, such tools impair selective reusability by creating external (inter-object) dependencies as a result of inheritance and encapsulation. Visual programming techniques facilitate the author's task of creating complex applications, but still frequently require scripting and/or programming to modify an object's characteristics or to model inter-object communication. The visual interface, at best, masks the programming mat controls die user's application beneath the surface. In any event, the external dependencies remain, and reusability is impaired. Other systems employ "pseudo-OOP" techniques in an attempt to combine die power of reusable objects with the flexibility of customizing the characteristics of particular objects and modeling inter-object communication. Forms-based authoring systems, such as Apple Computer's HyperCard™ and Microsoft's Visual Basic™, provide authors with significant freedom to create and configure individual objects using highly visual interfaces. Yet, such systems still rely heavily on scripting to implement an object's functionality, as well as inter-object communication and other forms of interaction. Though these systems often contain many built-in types of objects, it is extremely difficult to create new object types. An object's unique characteristics therefore are determined by its script. Because objects communicate with one anomer directly via scripts, these scripts are highly dependent upon one another, and cannot easily be reused in odier environments. Moving an object from one environment to another generally requires reading die scripts not only for that object, but for odier objects in its former environment. One category of products (e.g. , Apple Computer's Apple Media Tool™) provides a highly visual approach to authoring widi virtually no scripting or programming involved. In odier words, as opposed to visual programming languages (which, in essence, are merely "easy to use" scripting languages), such products provide true "object-based audioring" — i.e., the aud or creates and 10 configures actual instantiated objects (or pseudo-objects) with little or no scripting or programming. One problem with such tools is d at diey are extremely limited and inflexible. Authors typically cannot create custom events or messages, much less add functionality to an existing object or group objects together in any meaningful way. Moreover, such systems provide no mechanism for modeling modular "container" relationships among objects, and reusing diese more complex "user objects" in different container environments. All of the approaches noted above suffer from a lack of support for the creation of complex "user objects" that can be selectively reused in other environments. An object is only reusable to the extent diat its dependencies on its external environment are isolated within (i.e., known to) that object. An object is only selectively reusable to the extent that it is loosely coupled to die objects it contains, diereby permitting audiors to modify this relationship. What is needed is a system that models this "container" relationship among objects in a manner that permits authors to selectively reuse object containers and die objects they contain across different container environments. π. SUMMARY OF THE INVENTION. The present invention encompasses an application development system mat enables its users to create reusable "object containers" merely by defining links among instantiated objects. Employing a technique referred to herein as Hierarchical Encapsulation, die system automatically isolates the external dependencies of the object containers created by its users. This isolation of external dependencies resolves the problems addressed above regarding selective 11 reusability of "user objects," thereby facilitating the development of applications of increasing complexity. Objects contained widiin other objects are not "hidden" within or tightly coupled to their object container environments. Rather, they are loosely coupled widi d ose environments, and dierefore can more easily be reused in odier environments. By virtue of being contained within another object, the contained object automatically is afforded access to its environment. Its object container is, in essence, an "environmental frame of reference" for the objects it contains. For example, unless overridden by the audior, objects automatically receive messages sent to their object container. They automatically can access data known to their object container. Their position is even determined relative to their object container. Moreover, objects are decoupled from dieir characteristics. By defining two distinct types of objects (one of which modifies the characteristics of the other), and loosely coupling (i.e. , temporarily linking) these two types of objects, the system provides a mechanism for aumors to modify an object's characteristics merely by deeming one object to be contained within anomer. Removing that object from its container removes that characteristic. In this manner, authors easily can modify an object's characteristics and reuse it in other environments. In one embodiment described herein, die system is optimized for the development of interactive multimedia applications or "titles. " This multimedia authoring system provides its users ("authors") with a visual authoring interface that requires little, if any, scripting or programming. The system employs a form of object-based authoring in which aud ors create and configure instantiated objects directly, typically by "dragging and dropping" icons and configuring dialog boxes. Auώors can create two basic types of objects: Elements and Modifiers. Elements represent the actual characters or actors that interact with one another in 12 SUBSTTfUTE SHEET RULE 26 the author's title. Elements generally can be linked to external media (such as text, sounds, pictures, animations and movies), and possess certain inherent characteristics relating to that media. Audiors can supplement an Element's inherent characteristics by incorporating Modifiers within that Element. These Modifiers provide the Element with properties (known as Variables) diat furdier define what die Element IS and capabilities d at further determine what the Element does. A special type of Modifier, known as a Behavior, can contain additional Behaviors and other Modifiers, providing die author with a mechanism to create a complex Element "personality. " Both Elements and Behaviors are "object containers" — in this embodiment, object instances that can "contain" (i.e., be linked to) other object instances. Elements can contain Modifiers as well as other Elements; and Behaviors can contain Modifiers, including odier Behaviors. By incorporating Elements within Elements, authors create a Structural Hierarchy of Elements, each Element providing an environmental "frame of reference" for the Elements it contains. These "parent" Elements enable authors to provide structure for their titles and to model relationships among dieir Elements. Elements can communicate with one another at a high "Element level, " widiout regard to dieir child Elements. In one respect, Elements "encapsulate" their child Elements by creating a modular interface through which an Element's child Elements can communicate with objects external to that Element container. Similarly, by incorporating Behaviors (and other Modifiers) within Behaviors, all inside an Element, authors create a Behavioral Hierarchy within the 13 Element — i.e., the Element's internal "personality." Within the context of an Element "personality," each Behavior provides an environmental "frame of reference" for the Modifiers it contains. These "parent" Behaviors enable authors to model the relationships among the various Behaviors widiin an Element's overall personality. Elements, in effect, "inherit" the characteristics provided by dieir internal Behavioral Hierarchy. Because Elements and Modifiers are distinct, loosely coupled objects, authors can modify an Element's characteristics merely by adding Modifiers to (or removing Modifiers from) an Element. The system provides for significant reusability of object containers by utilizing the Structural and Behavioral Hierarchies to isolate the external dependencies of Elements and Behaviors. In essence, d e system automatically "encapsulates" an aumor's object containers. Once encapsulated, diey can be reused in other "environments." Moreover, by loosely coupling an Element to the Modifiers it contains, the system enables authors to modify dieir Elements so as to "inherit" and "disinherit" characteristics while maintaining an evolving hierarchical encapsulation vis-a-vis the Element's external environment. Using a technique known as Adoption, an author can cause an Element to be "adopted" by a new parent Element. Using a similar technique known as Transplantation, an audior can "transplant" an Element's Behavior (or its entire "personality") into anodier Element. Because Hierarchical Encapsulation is integrated into the Structural and Behavioral Hierarchies determined by d e audior's object containers, authors obtain the benefits of this technique automatically. Their Elements and Behaviors are thus selectively reusable. 14 For example, a mechanism known as Hierarchical Message Broadcasting provides a structured messaging system mat broadcasts messages from their initial destination down die Structural and Behavioral Hierarchies to all descendant Elements and Modifiers. This mechanism isolates an object container as a centralized abstract destination for all messages intended for "any object within that object container. " This mechanism facilitates reusability of object containers in other environments in mat an object container's new "parent" Element will provide it with messages automatically. Anodier mechanism, known as Hierarchical Variable Scoping, makes a Variable accessible automatically to all descendant objects of the Variable s parent Element or Behavior. This mechanism isolates an object container's dependencies on Variables diat are external to diat object container, but still within its ancestfal "environment." By making such Variables "known" to diose objects in the object container that rely on that Variable, the object container can be moved to anodier environment with a well-defined external interface that "knows" which external Variables are assumed to be present in diat environment. Yet another mechanism, known as Hierarchical Relative Positioning, determines the position of a child Element relative to the position of its parent Element. As a result, the child Element moves widi its parent Element automatically. This mechanism isolates an Element's external positional dependencies — i.e. , the effects of an Element's environment on the Element's position. In addition to the "built-in" Elements and Modifiers, the system is quite extensible via a "Component API. " This Component API enables programmers to seamlessly integrate new Modifiers (and "Services" that support them) into the system. 15 Finally, the architecture of die system is substantially platform-independent. Titles can be "played" on multiple platforms. Moreover, d e entire authoring environment can be ported to a variety of platforms widi relatively little modification due to the isolation of a platform-dependent layer within the system. m. BRIEF DESCRIPTION OF THE DRAWINGS. Fig. 1 is an illustration of the dual hierarchy (Structural and Behavioral) underlying die principles of the present invention. Fig. 2 is a screen display showing die layout view window, tool palette, object information palette and menus of the graphical user interface of the implementation of one embodiment of d e present invention. Fig. 3 is screen display showing the layers view window of the graphical user interface under one embodiment of d e invention. Fig. 4 is a screen display showing the sttucture view window of the graphical user interface under one embodiment of d e invention. Fig. 5 is a screen display showing die asset palette of the graphical user interface under one embodiment of the invention. Fig. 6 is a screen display of showing a library window in die graphical user interface under one embodiment of the invention. Fig. 7 is a screen display showing the alias palette of the graphical user interface under one embodiment of die invention. Fig. 8 is a screen display showing the messaging log window of the graphical user interface under one embodiment of die invention. Figs. 9(a)-(d) are screen displays showing die mToon editor windows of the graphical user interface under one embodiment of d e invention. Fig. 10 is a screen display showing the Element configuration dialog of the graphical user interface under one embodiment of die invention. Fig. 11 is a screen display of a Behavior configuration dialog in die graphical user interface under one embodiment of the invention. Figs. 12(a)-(h) are screen displays showing die Modifier configuration dialogs for Variables in the graphical user interface under one embodiment of d e invention. Figs. 13(a)-(g) are screen displays showing the Modifier configuration dialogs for Messengers in the graphical user interface under one embodiment of the invention. Figs. 14(a)-(c) are screen displays showing the Modifier configuration dialogs for Scene-based Modifiers in the graphical user interface under one embodiment of the invention. Fig. 15 is a diagram showing the operation of die Scene change Modifier of Fig. 14(a) in conjunction with die return Scene Modifier of Fig. 14(b). Figs. 16(a)-(d) are screen displays showing die Modifier configuration dialogs for Motion Modifiers in die graphical user interface under one embodiment of the invention. 17 Figs. 17(a)-(d) are screen displays showing die Modifier configuration dialogs for Graphics Modifiers in die graphical user interface under one embodiment of the invention. Figs. 18(a)-(d) are screen displays showing d e Modifier configuration dialogs for Sound Modifiers in the graphical user interface under one embodiment of the invention. Fig. 19 is a screen display showing the Modifier configuration dialog for die style Modifier in die graphical user interface under one embodiment of the invention. Fig. 20 is a screen display showing the Modifier configuration dialog for die cursor Modifier in d e graphical user interface under one embodiment of die invention. Fig. 21 is a screen display showing die Modifier configuration dialog for d e set Miniscript Modifier in die graphical user interface under one embodiment of the invention. Fig. 22 is a screen display showing die Modifier configuration dialog for the classification Modifier in die graphical user interface under one embodiment of die invention. Fig. 23 is a screen display showing die Modifier configuration dialog for the set value Modifier in d e graphical user interface under one embodiment of die invention. Fig. 24 is a high level block diagram of the implementation of one embodiment of the present invention. 18 Fig. 25 is a diagram showing die interconnection of the various classes in die object model of the present invention. Fig. 26 is a diagram showing d e interconnection of die Service classes in the object model of die present invention. Fig. 27 is a diagram showing me storage layout for a multimedia title in one embodiment of the present invention. Fig. 28 is a flowchart showing die event processing loop under one embodiment of the invention. Fig. 29 is a diagram showing the architecture of bo the Component API and audioring GUI according to the present invention. Fig. 30 is a diagram showing die operation of the object model of die present invention. Fig. 31 is a flowchart showing the loading of Components (Modifiers, Services) at boot-up time of the program under one embodiment of die invention. Fig. 32 is a screen display showing an implementation of a snake. Fig. 33 is a screen display showing an implementation of a school of fish. Figs. 34(a)-(g) are screen displays of a selectively reusable windowing system. Figs. 35(a)-(g) are diagrams showing the implementation of the selectively reusable windowing system. 19 IV. DETAILED DESCRIPTION. A. External Architecture — "Author's-Eve View". Before discussing the underlying implementation of the authoring system of the present invention, it is helpful to examine its external architecture — i.e. , that portion of the system which is visible to the author. It is through this external architecture diat authors create end-user applications or "titles." As is explained in greater detail below, programmers can extend d e functionality of mis external architecture, seamlessly, via an interface to the "core" of me system. Moreover, the platform- independent nature of the system's implementation facilitates portability of the efforts of authors and programmers to a wide variety of computing platforms. 1. Objects: Elements and Modifiers. In one embodiment of this invention, the audior can create two basic types of objects: Elements and Modifiers. To use die metaphor of a stage play, the Elements comprise the play's structure (e.g. , acts and scenes) and its actors, and the Modifiers comprise the stage directions, the motivations the director imbues in die actors to behave d e way they do, and other modifications to me characteristics of the play's structure and its actors. The system enables authors to create various types of Elements and to assign particular characteristics to each Element. These characteristics include properties (e.g. , weight, color, etc.) diat define what the Element is and capabilities (e.g., send messages, move along a path, etc.) that determine what me Element does. Authors assign characteristics to an Element by incorporating Modifiers widiin that Element. As is illustrated below, the process of creating and configuring Elements and Modifiers is highly visual and intuitive, typically involving "dragging and dropping" icons representing Elements and Modifiers, selecting menu items and configuring dialog boxes. Little, if any, scripting or programming is required. The system is, however, quite extensible via the "Component API. " discussed in greater detail below. Programmers can use the Component API to create "Components" that become fully integrated Modifiers and "Services" (which "service" Modifiers but are not accessible directly to audiors). Once created, Components are indistinguishable from the system's "built-in" Modifiers and Services. In this embodiment, mere are three general categories of Modifiers: (i) Variables diat simply store data of various types; (ii) Capabilities diat perform actions on behalf of die Element; and (iii) Behaviors that "contain" additional Behaviors and odier Modifiers. In another embodiment, a hybrid Variable/Capability Modifier could both store data and perform actions. An author can create two general categories of Elements: (i) Structural Elements (including Projects. Sections and Subsections, discussed in greater detail below) that serve only to "contain" odier Elements and Modifiers; and (ii) Media Elements (including Scenes, discussed below) that not only can contain other Media Elements and Modifiers, but also can be "linked" to raw media, such as text, sounds, pictures, animations and movies. There are diree basic types of Media Elements mat an audior can create: (i) Graphic Elements (including still pictures, animations and videos), Text Elements and Sound Elements. An author can then link raw media of a particular 21 format to the Element, causing that Element to attain certain inherent capabilities (e.g. , to make a sound, display a picture, or play a movie). By linking raw media of a particular format to a Graphic, Text or Sound Element, the author causes die system to "morph" die Element into a more specific type of Element (and among specific types) related to that format. For example, the audior could create an "AIFF" sound, an "ASCII" sentence, a "PICT" picture, a "QuickTime" movie or an "mToon" (a built-in animation format). The morphing process is described in greater detail below widi respect to die system's implementation. Elements of a given type also have certain built-in properties known as Attributes. An Element's Attributes include properties applicable to die type of media to which the Element is linked (e.g. , position, eel number, rate, etc.). Thus, an Element's properties are defined by its Attributes and its author-created Variables. An Element's capabilities are determined by d e type of media, if any, to which it is linked, and by its author-created Behaviors and Capabilities (i.e., its non- Variable Modifiers). Together, diese properties and capabilities define an Element's individual characteristics — i.e., what the Element is and what d e Element does. In addition to creating Elements and assigning d em individual characteristics, an author can specify die manner in which these Elements interact with one anodier, via an integrated object messaging mechanism. This messaging mechanism is accessible to authors via Modifiers, as is described in greater detail below. 22 2. Object Containers: Elements and Behaviors. Unlike simple "leaf" objects, Elements and Behaviors are "object containers" that can comprise a hierarchy of objects. These object hierarchies provide "environments" (each enclosed by an object container) in which the system can isolate external dependencies. This isolation of an object container's external dependencies, referred to herein as "Hierarchical Encapsulation." results in a significant degree of reusability of the Elements and Behaviors created by an audior. As is illusttated below, authors can construct complex environments comprising a hierarchy of "Elements within Elements" interacting with one anodier. Within an Element, authors can create equally complex internal environments (together representing d e Element's "personality") comprising a hierarchy of interrelated "Behaviors and odier Modifiers within Behaviors." Audiors can selectively reuse diese modular Element and Behavior object containers at virtually any level of complexity. Moreover, authors can "mix and match" Elements and Modifiers from differing environments at practically any level of the Structural and Behavioral Hierarchies. Furdiermore, a team of audiors can collaborate to create and test an entire application while individual authors refine dieir own modular, self-contained environments. For example, multiple authors might collaborate to build a complex model of a "car" Element that contains one "engine," four "wheel" and various other Elements, as well as a "driving" Behavior that contains "steering," "braking" and various odier Behaviors. Individual audiors each might create one or more of these self-contained Elements and Behaviors, and then collaborate with one anodier to test all or a portion of the "car" and refine the desired interaction among the various Elements and Behaviors. 23 Moreover, a subsequent author working on a different application could reuse die entire "car" Element or merely one or more of the Elements or Behaviors contained therein. For example, the author might apply the "braking" Behavior to a "horse" or "airplane" Element in another application. To create complex objects, authors need not create abstract "classes" or object templates that serve to relate objects to one another widi respect to their characteristics. Elements, Behaviors and other Modifiers created by die author are object instances. To permit Elements and Behaviors to "contain" other objects, the system links the Element and Behavior object instances to the odier object instances contained within them (as is explained in greater detail below with respect to the system's implementation). Thus, Elements and Behaviors are object containers — in this embodiment, object instances diat can "contain" (i.e., be linked to) other object instances. To some extent, however, Elements do attain (at least temporarily) the characteristics diey contain. Yet Elements merely provide an environmental frame of reference to their descendant Elements. Elements and Behaviors do not actually "inherit" the characteristics of die objects they contain. Many embodiments of this "object container" relationship among objects are possible, including intersecting families of objects, multiple-parent relationships and various combinations of "one-to-many" and "many-to-many" child-parent relationships. In any event, by spawning object hierarchies, object containers provide die environments that facilitate their reusability via Hierarchical Encapsulation, discussed below. Authors are thus free to create and work directly widi objects that represent, at any level of complexity, me characters in their application and die individual characteristics "contained within" those characters, as well as the all-encompassing "environmental factors" that "contain" those characters and determine the nature of their interaction. 3. Object Hierarchies: Structural Hierarchy and Behavioral Hierarchy. When an Element contains another object widiin it, die Element object is called a parent and the odier object is called its child. If the child object in turn contains another object, the child object is considered die parent of the object it contains, and so on. This chain of parents and children is called an Element or (Structural) Hierarchy. In one embodiment, each parent can have multiple children, but each child has exactly one parent. Elements above and below a particular Element in die Structural Hierarchy can be referred to, respectively, as ancestors and descendants of diat Element. Children of the same parent are called siblings. Just as an Element can contain other Elements in the Structural Hierarchy, each Element also contains its own Modifier or Behavioral Hierarchy of Behaviors and "leaf" Modifiers (i.e. the Element's personality). These Modifiers modify the characteristics of die Element (e.g., by storing data in the Element or performing actions on behalf of the Element), often in response to messages from other Modifiers inside the same or another Element. In die context of die Structural Hierarchy, an Element can be viewed as an environmental "frame of reference" for its descendant Elements. It is within that Element's environment that its descendant Elements exhibit their personalities. The Su-uctural Hierarchy determines the manner in which those descendant Elements interact with one anodier within diat Element's environment. 25 Similarly, the Behavioral Hierarchy determines die manner of interaction among an Element's internal Behaviors. In the context of die Element's overall personality, a Behavior also can be viewed as an environmental "frame of reference" for its descendant Behaviors and odier Modifiers. Continuing our "car" example, die "car" Element provides die environment in which die "engine" Element functions. If the car moves, the engine will move with die car automatically (as it would in a real car). Yet, the engine Element need not have any internal "movement" Behavior. By acting as die local coordinate system for its child Elements, the car becomes the engine's environmental frame of reference. This particular manner of isolating positional dependencies of Elements within the Structural Hierarchy, referred to as Hierarchical Relative Positioning, is discussed in greater detail below. Similarly, die "driving" Behavior provides die environment in which die "braking" Behavior functions. If the driver does not step on die brakes, the "braking" Behavior will not be invoked — i.e. , it will not receive a "brake pedal depressed" message from its parent "driving" Behavior. By acting as the "gatekeeper" for messages intended for its child Behaviors, die parent "driving" Behavior becomes the "braking" Behavior's environmental frame of reference. This particular manner of isolating messaging dependencies of Elements and Behaviors (and other Modifiers) widiin the Structural and Behavioral Hierarchies, referred to as Hierarchical Message Broadcasting, is discussed in greater detail below. Continuing the example, die "driving" Behavior must monitor the car's speed for a variety of reasons, as must the driver of a real car (e.g., to know when to release die brake). The speed of the car could be stored in a "car speed" Variable inside die Element, but not necessarily inside the "driving" Behavior because other Behaviors (e.g., an "Air Bag" Behavior detecting massive deceleration) may need to access this Variable. By making its child Variables accessible to its descendants, the car becomes the frame of reference for the "driving" Behavior. This particular manner of isolating data dependencies of Elements and Behaviors (and odier Modifiers) within die Structural and Behavioral Hierarchies, referred to as Hierarchical Variable Scoping, also is discussed in greater detail below. a. Types of Elements in the Structural Hierarchy. As noted above, there exist two basic categories of Elements in mis embodiment — Structural Elements and Media Elements. Authors can utilize Su-uctural Elements to group the contents of a title into organized sections, like die chapters of a book or the acts in a play. In this embodiment, the purely Structural Elements comprise Projects, Sections and Subsections. Media Elements (including the Modifiers contained within diem) comprise the primary content of an audior's application. They typically are the characters or actors widiin a "Scene" (a special Media Element the primary purpose of which is structural — to contain other Media Elements). Any Media Element can be used structurally, as containers for other Media Elements, to form a more complex Element. Media Elements as their name suggests, typically are linked to raw media, such as text, sounds, pictures, movies or animations, in order to communicate widi the user of the title. (1) Projects. A Project is a Structural Element that contains the entire title. Its children are Sections, which are described below. A Project also can contain Modifiers (including Behaviors) diat store data or perform actions on behalf of the entire 27 Project. The score of a game, for example, could be stored in the Project so as to be available to all other Elements and Modifiers. (2) Sections. A Section is a Structural Element that can be used by the audior to organize logical portions of his title. It is most analogous to an act in a play or a chapter in a book. For example, an author of a U.S. travel game might create a Section for all Elements and Modifiers relating specifically to die state of California. Sections are parents to Subsections, as described below. As widi Projects, Sections also can contain Modifiers. A "time- in-state" Behavior might, for example, track the amount of time the user spent in a particular state. (3) Subsections. A Subsection is a Su-uctural Element that can be used by die author to furdier organize logical portions of a Section. Continuing the above example, the author of die travel game might create a Subsection for all Elements and Modifiers relating specifically to die San Francisco Bay Area. Subsections are parents to Scenes, and also can contain Modifiers. (4) Scenes. A Scene is a special Media Element that not only furdier organizes logical portions of a Subsection, but also contains other (non-Scene) Media Elements and Modifiers. Much like die scenes in a play, die Scene Element contains those Media Elements and Modifiers die author deems necessary to impart to the user a portion of die interactive experience provided by the parent Subsection. Continuing our travel game example, one Scene might take place on the Pacific Coast, while anodier occurs furdier inland in the city of Palo Alto. 28 In one embodiment, there exists a special type of Scene Element known as a Shared Scene. A Shared Scene is used to organize Elements that will be visible across multiple Scenes, such as a background picture or an animated character that travels from Scene to Scene. In a more refined embodiment, the audior can share visible Elements across Subsections and Sections by having multiple Shared Scenes, or being able to select one or more Shared Scenes dynamically. In die latter case, rather dian designating a Shared Scene statically at "authoring time," the audior can, dynamically at "runtime," designate any Scene (or perhaps multiple Scenes) as a current Shared Scene. (5) Media Elements. Media Elements comprise the primary characters or actors in a Scene. They can contain other Elements (to form a more complex Element) and can be linked to raw media. A Media Element also can contain Modifiers, and thus Behaviors, which together constitute die Element's personality. As illustrated below, it is an Element's "dual hierarchy" that provides the environmental framework in which descendant Elements interact with one another and exhibit dieir own individual "personality. " b. Isolation of External Dependencies of Object Containers. Elements and Behaviors are object containers that spawn hierarchies of descendant objects. Consider die sample illusu-ation of the Structural and Behavioral Hierarchies in Fig. 1. When Media Elements are created, diey are positioned automatically below the Scene in die Project's Structural Hierarchy. Thus, Element El 108 is a child of Scene Scl 106 in Subsection SSI 104 in Section SI 102 in Project P 101. Element E4 111 is a child of Element El 108. By isolating the external dependencies of die environment created by an Element or Behavior object container, the system provides for a significant degree of selective reusability of that Element or Behavior (or any object contained therein) in other environments, as is further demonstrated below. It is this isolation of an object container's external dependencies diat allows die Elements and Behaviors created by an author to become an "environmental frame of reference" for dieir descendant Elements, Behaviors and odier Modifiers, as was demonstrated in die "car" example discussed above. In one embodiment of this system, three mechanisms are employed to isolate external dependencies within object containers: (i) Hierarchical Message Broadcasting — messages that are received by an Element or Behavior typically are "broadcast" down the Structural and Behavioral Hierarchies to its descendant Elements and Modifiers (diough this effect can be overridden); (ii) Hierarchical Variable Scoping — Variables are accessible to all descendant Elements and Modifiers of that Variable's parent Element or Behavior; and (iii) Hierarchical Relative Positioning — an Element's position in the Scene is determined relative to die position of (i.e., using the local coordinate system of) its parent Element, and therefore changes as the position of its parent Element changes. (1) Hierarchical Message Broadcasting. A message sent to an Element or Behavior typically will be broadcast down die Structural and Behavioral Hierarchies. Elements pass down messages to their children, be d ey Modifiers or odier Elements. Behavior pass down messages to dieir child Modifiers. The precise manner in which the various types of messages propagate down die Structural and Behavioral Hierarchies is discussed in greater detail below with respect to object messaging generally. In one embodiment, the order in which messages are broadcast among Elements, Behaviors and odier Modifiers at any given level of die Su-uctural and Behavioral Hierarchies is determined by the order in which those objects appear in the "structure view window" (see, e.g. , structure view window 330 in Fig. 4). Initially, this is the order in which diey are created. The audior can modify this order simply by "dragging and dropping" or "cutting and pasting" the object's icon in the structure view window. For example, referring again to Fig. 1, a message sent to Scene Scl 106, under one embodiment, initially would be sent down to Element El 108 (but not to any sibling Elements of Scene Scl 106, such as Shared Scene ScO 107). It would then be sent down to Element E4 111, and dien to Element E2 109. From there it would be sent down to Modifiers Ml 114, M2 115 and M3 116, and dien to Element E3 110. It would then be sent down to Modifier M4 117, Behavior Bl 118 and then down to Modifier M5 119. Finally, it would be sent to Behavior B2 120 and then down to Modifiers M6 122 and M7 123. Note that, in this embodiment, Variables such as Variable V3 121 solely store data and dius do not respond to messages. Their data, however, can be read and written by other Modifiers, as for example, the Miniscript Modifier. In this manner, a message sent to an Element or Behavior typically will be broadcast to all objects contained widiin diat Element or Behavior. Upon receiving the message, those objects (Elements, Behaviors and odier Modifiers) can then respond appropriately, performing whatever actions are specified by their current configuration. By providing for the sending of messages to an Element or Behavior object container, and the broadcasting of diose messages to the objects within that container, die system facilitates the isolation of messaging traffic to and from that container. In essence, the container becomes a higher-level abstract destination for messages intended not only for the container itself, but for "objects within the container. " 31 Continuing the above example of the travel game, assume that Section S I 102 represents California, Section S2 103 represents Kansas and Subsection SSI 104 represents the San Francisco Bay Area. The author could create Behaviors to simulate die different weather patterns in diese two states. A "Midwest Weather" Behavior in Section S2 103 could simulate the weather in Kansas and periodically update a "temperature" Variable and send a "check temperature" message to mat Section S2 103, which would be broadcast down the Structural and Behavioral Hierarchies to all Elements and Modifiers in each Scene in Kansas. This Behavior and die temperature Variable could bodi be contained at the Section S2 103 level of the Structural Hierarchy to simulate relatively constant weather throughout the state of Kansas. Conversely, within California, Subsection SSI 104 (the San Francisco Bay Area) could contain two Scenes, one representing the Pacific Coast and the odier representing Palo Alto. These Scenes could contain "Coast Weather" and "Inland Weadier" Behaviors, respectively, each updating dieir own "temperature" Variable and sending a "check temperature" message to their respective Scenes. These separate Behaviors could simulate the differing weather patterns that occur even within a relatively small region of California. "People" Elements in the various Scenes widiin the two states might be very complex, perhaps containing five or ten different Behaviors, including a Jogging, Swimming and a "Check Temperature" Behavior mat check the temperature in response to a "check temperature" message. If the temperature deviates too far from the average temperature, me Check Temperature Behavior might send a "Very High Temperature" or "Very Low Temperature" message to its person Element, which will be broadcast down to the Swimming and Jogging Behaviors. The Swimming Behavior might be enabled by "Very High Temperatures" and disabled by "Very Low Temperature" and vice-versa for the Jogging Behavior. 32 By permitting the various "weather" Behaviors to broadcast dieir messages down die Structural and Behavioral Hierarchies (from the Section level in Kansas, and from the Scene level in California), the people Elements in either state will receive this message from their respective parent Scenes. The "weadier" Behaviors need not target their message directly to a particular person Element, or even know which type of Element might respond to their "check temperature" message (e.g. , person, animal, etc.). The people Elements, merefore, could be moved from any Scene in Kansas to any other Scene in Kansas or California, and still respond appropriately to the temperature in that region. Even diough the "check temperature" message is sent to a different environment or level of the Structural Hierarchy in Kansas (Section) than in California (Scene), it still reaches all relevant people Elements. This degree of reusability of Elements and Behaviors is facilitated by die system's Hierarchical Message Broadcasting mechanism, which broadcasts messages sent to an object container to the objects it contains. This mechanism isolates the dependencies of a message at die abstract level of die environment represented by die object container to which that message is sent, as opposed to requiring the audior to target the message directly to a particular "leaf" object. As is discussed below, direct targeting of messages remains an option in this embodiment in die event diat die audior elects to forego a degree of reusability in favor of explicit target naming. (2) Hierarchical Variable Scoping. As demonstrated above, Elements and Behaviors are dependent upon messages to enable, disable and trigger certain actions, including those of their descendant Modifiers. Those Modifiers frequently are dependent upon Variables to perform actions on behalf of their parent Elements. Isolating Variable 33 dependencies widiin Elements and Behaviors also facilitates reusability of those object containers. The scope of Variables (data) accessible to a Modifier is another manifestation of that Modifier's environment. Variables are accessible to all descendant objects of that Variable's parent Element or Behavior. In other words, Variables are accessible widiin their parent's environment. Hierarchical Variable Scoping serves to isolate an object container's dependencies on external Variables. By making Variables accessible to descendant objects of the Variable's parent, those descendant objects automatically "know about" those external Variables. A descendant Element or Behavior therefore becomes reusable in that the external Variables upon which it depends are isolated widiin ("known to") that Element or Behavior. Returning to our travel game example, the "temperature" Variable in Kansas is accessible to the "Check Temperature" Behavior within any person Element of any Scene in Kansas. Because the "temperature" Variable is located at die Section S2 103 level, its descendant Elements include all Subsections therein, each Scene contained widiin diose Subsections, each Element in each such Scene (including any people Elements), and finally the "Check Temperature" Behavior contained widiin such people Elements. Moreover, if a person Element was moved from a Scene in Kansas to die Pacific Coast Scene in California, the "temperature" Variable in that Scene would be accessible, automatically, to that person Element and to its "Check Temperature" Behavior. This degree of reusability is a direct result of die Hierarchical Variable Scoping mechanism. In me above example, this mechanism isolates "temperature" Variable dependencies at die Section level in Kansas and at die Scene level widiin the San 34 SUBSTITUTE SHEET (RULf 26) Francisco Bay Area in California. As noted above, die Hierarchical Message Broadcasting mechanism also isolates messaging dependencies (in particular die "check temperature" message) at those same levels of the Structural Hierarchy. Thus, in this example, these two mechanisms together make object containers below that level (such as the person Element) reusable across Sections of a Project. (3) Hierarchical Relative Positioning. Another environmental dependency of object containers, in this case limited to Elements, is the position of an Element relative to that of its ancestors. Rather dian require the author to model the common circumstance in which the movement of one Element must be relative to die movement of another Element, the system, by default, determines an Element's position in me Scene relative to the position of (i.e. , using the local coordinate system of) its parent Element. In another embodiment, this effect could be made optional. In any event, a child Element can, as part of its own personality, move on its own initiative. Its position nevertheless remains relative to its parent Element. It therefore also will continue to move as its parent Element moves. Thus, a child Element moves (changes position) within d e Scene as its parent Element moves. This effect filters down the Structural Hierarchy below the Scene level. A common use of Hierarchical Relative Positioning is to model Elements physically contained within or attached to other Elements (e.g. , a toy in a box or the wings of a bird). It also can be used to model Elements that, for one reason or anodier, tend to follow other Elements (e.g., planets orbiting the sun, or packs of animals that tend to move togedier). Hierarchical Relative Positioning also serves to isolate an Element's dependencies on its environment, in that an audior need not model this "follow my parent" movement. Upon reusing or reattaching an Element to another parent Element, the system automatically recalculates that Element's position relative to its new parent Element. c. Selective Reusability through Adoption and Transplantation. The selective reusability of object containers discussed above frequently takes one of two forms. If Elements are to be reused, they often will be placed in a new environment — i.e. , given a new parent Element in the Structural Hierarchy. This process is referred to as "Adoption. " In other words, d e child Element has been "adopted" by a new parent Element. The underlying implementation of Adoption is discussed in greater detail below. From the author's perspective, Adoption is a simple process at aumoring time. For example, referring to Fig. 2, me author can break its current link and create a new link with d e link tool 365 on the tool palette 36 with anodier Element in the layout view window 320. Alternatively, the audior can drag and drop die Element's icon to the icon representing its new parent Element in the Structure Window 33. Authors also may desire to move a Behavior or odier Modifier from within its parent Element or Behavior to another parent Element or Behavior. This process is referred to as "Transplantation." In other words, a Behavior or other Modifier, and its associated capabilities, are "transplanted" to a new Element or Behavior, which then acquires diose capabilities. Transplantation also can be accomplished quite easily at au ioring time, by dragging and dropping die icon representing die Behavior or Modifier from its old parent to its new parent, either in die Layout Window 320 or in the Structure Window 33. 36 Adoption and Transplantation are quite similar, both from the author's perspective and in view of die manner in which they are implemented, as is discussed in greater detail below. Both involve die transfer of an Element or Modifier to a new parent Element or Behavior. In odier words, both involve the selective reusability of an Element or Modifier in new environments. In a more refined embodiment, Adoption and/or Transplantation can be performed dynamically, at runtime. One author might, for example, desire to model certain gravitational forces that cause an Element "planet" orbiting another Element "star" to begin to orbit a new parent Element "rogue star" diat passes nearby. Anodier audior might desire to model a change in a person's behavior, in effect by transplanting a Behavior Modifier within die Element representing that person. As is discussed in greater detail below widi respect to die system's implementation, mis process is quite similar whedier performed at authoring time (referred to as "Edit Mode") or at runtime (referred to as "Runtime Mode"). Depending upon the nature of the Adoption or Transplantation the author desires (or perhaps desires to provide to the user), different functions can be accessed via die Component API. Similarly, a programmer can, via the Component API, provide dynamic (runtime) instantiation of objects, such as Elements and Modifiers. This process, referred to as "Dynamic Creation. " also is discussed below with respect to die system's implementation. 4. Object Authoring Interface. Figs. 2-9 show some of the features of the object authoring interface. They include die layers view window 310 (Fig. 3), layout view window 320 (Fig. 2), structure view window 330 (Fig. 4), modifier palettes 35a and 35b (Fig. 9), tool palette 36 (Fig. 2), object information palette 37 (Fig. 2), menus 38 (Fig. 2), asset palette 70 (Fig. 5), alias palette 80 (Fig. 7), mToon editor windows 900, 910, 920 and 930 (Fig. 9), and messaging log window 420 (Fig. 8). Widi reference to Fig. 2, die tool palette 36 is provided with a variety of functions, including: (i) a pointer 361 for selecting, clicking, dragging, scrolling, etc.; (ii) a graphic tool 362 for creating Graphic Elements; (iii) a text placeholder tool 363 for creating Text Elements; (iv) a cropping tool 364 to crop and link non- animated Graphic Elements; (v) a linking tool 365 for linking Elements into a parent/child relationship; (vi) a hand tool 366 to offset media within Elements, as well as (vii) a background/foreground color tool 367 for selecting the background and foreground colors of an Element. The object information palette 37 displays an Element's position in x 328 and y 329 coordinates, size in x 336 and y 331 coordinates, scale in x 332 and y 333 coordinates, and odier data related to a selected Element, such as die Element's name 326, die name of its parent 327, its layer order number 335 and, in d e case of an mToon, its eel number 334. In the "Hierarchical Relative Positioning" embodiment discussed herein, die position of the Element is given relative to its parent. The menus 38 allow access to all other functions not accessible odierwise from die present on-screen features. Menu 338a is die "Apple" menu under die Macintosh™ operating system with its well known features. The functions of the remaining menus are described below. "File" menu 338b allows authors to create new Projects, libraries and mToons, to open existing Projects, to close windows, to save projects under die current or another name, to link Elements to media in a particular file or resources folder. Menu 338b further allows audiors to break media links, to run a Project 38 TE SHEET 26 from either the start or from a given selection, to build a title from the current Project, or to quit the application. "Edit" menu 338d allows authors to perform the usual undo, cut, copy, paste, clear, "select all" and duplicate functions, as well as create author messages and set application and Project preferences. "Format" menu 338d allows authors to set font, font size, font style and text alignment characteristics for selected text. "Arrange" menu 338e allows authors to align objects, to adjust their sizes, to move them completely forward or backward in the layer order, or incrementally so, as well as to adjust for any gaps in layer order created by such operations. "Object" menu 338f allows audiors to create new Sections, Subsections, Scenes, Graphic Elements, Sound Elements and Text Elements, to access the Element information dialog 950 (Fig. 10), to revert to die default size of an object, to lock an object's settings, to find items by name, as well as to make and break aliases. "View" menu 338g allows authors to open the layout view window 320, the structure view window 330, the layer view window 310, die tool palette 36, the modifier palettes 35a and 35b, die alias palette 80, die asset palette 70, the object information palette 37 and die messaging log window 420. In addition, audiors can use menu 338g to preview the effects of selecting different color tables, to show or hide Element frames, Modifier icons, object names, low resolution (draft) object images, the Shared Scene, as well as to synchronize all windows to reflect information for the same object. "Window" menu 338h allows authors to access all currently open windows. 39 a. Layout View. The layout view 32 is used to edit a Scene of a Project. Again with reference to Fig. 2, die basic operation of the layout view 32, through layout view window 320, is as follows. The layout view window 320 represents Projects at a Scene level, thus acting as a stage in which authors can arrange their Media Elements. To bring the appropriate Scene into the layout view window 320, pop¬ up menus 321, 322 and 323 are provided to navigate, respectively, among a Project's Sections, Subsections and Scenes. These pop-up menus 321, 322 and 323 also have "New Section", "New Subsection" and "New Scene" items, as an alternative to using Object menu 338f to create such Structural Elements. Back arrow 324a and forward arrow 324b are an alternate means of accessing the previous and next Scenes widiin the current Subsection. Forward arrow 324b is dimmed to indicate diat the current Scene is the last Scene in die current Subsection. Shown widiin die content region of layout view window 320 is a Graphic Element 337 containing Graphic Modifier 338. b. Layers View. The layers view 31 is used to edit Projects a Section at a time through the layers view window 310. With reference to Fig. 3, die basic operation of the layers view window 310 is now described. The layers view window 310 presents a matrix of Media Elements, arranged by Scene order on the horizontal axis and layer order on die vertical. Layer order is die order in which Elements are drawn on the screen, meaning that a Scene is layer order 0, and all the Scene's contained Elements progress in increments of 1 dierefrom. Layer order is particularly useful to create d e illusion diat die two dimensional (X,Y) screen has a depth (Z) dimension, an effect referred to as "2.5D. " The layer order can easily be changed by dragging and dropping an Element over another Element, although this may also be accomplished through menus 38. Either way, die user performs such operations as bring to front (make layer order die highest), send to back (make layer order 1), bring forward (exchange layer order widi next highest) or bring backward (exchange layer order with next lowest). Scenes are assigned layer order 0, which cannot be changed by die author, and are dius always in die background. The layers view window 310 contains pop-up menus 311 and 312 that navigate among a Project's Section and Subsections, respectively, in a manner similar to the pop-up menus 321 and 322 of the layout view window 320. Furdiermore, back and forward arrows 313a and 313b act to select Subsections much as arrows 324a and 324b navigate through Scenes in die layout view window 320. Thus, in this example, one can see columns arranged horizontally for Shared Scene 314a, Scene 1 314b, Scene 2 314c and Scene 3 314d. Vertically, one can see rows for layer order 0 (Scene) 318a, layer order 1 318b and layer order 2 318c. Along row 318a, one can see the background pictures for the respective Scenes 315a, 315b, 315c and 315d, as well as four non-Scene Media Elements (Element 316a and 316d under Scene 1 315b, Element 316b under Scene 2 315c, and Element 316c under Scene 3 315d). Modifiers are also shown widiin Elements (widi Modifiers 317a, 317b and 317c in Shared Scene 314a, Modifiers 317d, 317e and 317f in Scene 3 315d, Modifier 317g in Scene 1 315b, Modifier 317h in Scene 2 315c, Modifiers 317i and 317j in Element 316a, and Modifier 317k in Element 316c). Elements and Modifiers can be dragged and dropped widiin layers view window 310. In particular, an Element's layer order can be modified easily by dragging and dropping it onto an Element in another layer, causing all Elements to be "pushed up" one layer higher. c. Structure View. The structure view 33 allows audiors to move Elements and Modifiers throughout the Su-uctural and Behavioral Hierarchies - i.e., across Projects, Subsections and Scenes, as well as widiin Elements and Behaviors. Structure view 33 generates and condOls the operation of structure view window 330, shown in Fig. 4. The Structural Hierarchy is plainly evident in diat Project "Untitled-1 " 303 is at the top, with Section "untitled section" 304 immediately below and indented with respect to the Project 303 icon, Subsection "untitled subsection" 305 immediately below and indented with respect to die section 304 icon, Scene "untitled Scene" 306 immediately below and indented widi respect to the Subsection 305 icon. In this instance the Scene 306 icon represents a Shared Scene, to which a Graphic Modifier 308 is attached. The Subsection 305 has another child Scene 307, being the actual first Scene, which is represented as equally indented as its sibling Scene 306. Under this Scene 307 is Media Element 300. Knobs 302a, 302b, 302c, 302d, 302e and 302f are used to reveal or conceal the objects beneath Elements 303, 304, 305, 306, 307 and 309, respectively, in the Sumctural Hierarchy. This is particularly useful for an author who wishes to concentrate on only part of the Project at a given time. Changing the hierarchical relationship through the structure view window 330 is particularly simple. Elements may be dragged up and down and dropped into the Su-uctural Hierarchy at will, subject to a few limitations. For example, a Media Element cannot be dropped directly into a Project, Section or Subsection. Similarly, Scenes cannot be dropped into to a Section or Project. In addition, only Modifiers can be dropped into Behaviors. d. Asset Palette. The Asset Manager 7, operating dirough the Asset Palette 70, illustrated in Fig. 5, is a visual database of the media diat have been linked to a Project. This 42 palette makes linking, storing, and copying Graphic and Sound Elements easy and convenient. Each item can then be dragged and dropped onto Scenes from this central location. Each time a new asset is added to the Project, it gets added to the Asset Manager 7, which adds it to the Asset Palette 70 in a manner that is transparent to the author. Once an asset is in the Asset Palette 70, it can be used by multiple objects in the Project. For example, a single animation file can be linked simultaneously to multiple Elements. Each Element can use mis animation without regard to die other Elements. Each enϋ-y in the Asset Palette 70 includes an associated count of the number of objects which use that asset. When an asset is no longer in use (i.e. its count becomes zero), it still remains in the Asset Palette 70. Each time the audior performs a link to media, an asset appears in the Asset Palette 70. "Show" pop-up menu 751 displays media files by selected types (e.g., all types, all graphics types, PICTs, mToons, sounds, QuickTime™ movies, or color tables). "View" pop-up menu 752 displays assets either as icons or as small or large thumbnails. Trash can icon 753 allows audiors to remove assets from the palette by dragging diem to the trash can. There are multiple assets 754a, 754b, 754c, 754d shown here. For example, asset 754c is a sound, represented by a sound icon and having a preview button to allow the author to hear the sound. e. - Library. Libraries offer a convenient place to store Elements and Modifiers for use across Projects. Authors can create multiple libraries, and can have more than one open at once. Authors can move Elements and Modifiers freely between any Project and any library. Any object, from a simple Modifier to an entire Scene, Subsection, Section, or Project (at any stage of development) can be dragged between libraries and Projects. 43 With reference to Fig. 6, the operation of a view 520 of one of die libraries 52 is shown. It includes the library's name 726, a close box 727, a trash can icon 728 which allows authors to remove items from the library by dragging diem to the ti-ash can, a "save" pop-up menu which allows audiors to save the library to disk, and, as shown here, multiple objects 729a, 729b, 729c, 729d, 729e and 729f in the library. f. Alias Palette. An alias is a programming tool that enables authors to maintain identical settings across multiple Modifiers. When a Modifier is "aliased" initially, a master copy is placed in the Alias Palette 80. Authors can create additional aliases that refer to diat master copy merely by duplicating any aliased Modifier. The advantage of using aliases lies in the fact that diey are globally updatable. Changing the settings of one "instance" of an alias alters the settings of its master copy in the Alias Palette 80 and automatically updates die settings of each of the other instances of diat alias throughout d e Project. Variables are good candidates for aliasing. For example, a game score can be stored and aliased. This Variable can then be strategically placed in Elements far apart in the Structural Hierarchy. Messengers and Miniscript Modifiers in these Elements can access and update dieir "local copy" of this Variable, which in turn will access die master copy, thereby ensuring synchronization across all "local copies" of this Variable. In this manner, various Elements, regardless of dieir location in the Structural Hierarchy, will have access to the updated score as die value of this Variable changes during die game. Breaking an alias causes me formerly aliased Modifier to become an independent Modifier, no longer updated when its former aliases are modified. Widi reference to Fig. 7, Alias Palette 80, controlled by Alias Manager 8, includes a close box 854, a trash can icon 851 which allows authors to remove aliases from the palette by dragging diem to die trash can, and, as shown here, multiple aliases 852a, 852b, 852c, 852d, 852e and 852f, with respective user counts 853a, 853b, 853c, 853d, 853e and 853f. The user count reveals the number of instances of such alias within the current Project. Thus, if a new alias is created, a new entry in the Alias Palette 80 is added. If a modifier is de-aliased or deleted, die corresponding user count on die Alias Palette 80 is decremented. g. Messaging Log. Messaging Log 42 allows authors to "debug" dieir Projects by maintaining for authors a log of particular messages sent to selected objects during Runtime execution. It displays diese messages in messaging log window 420, as illustrated in Fig. 8. The "Enable Logging" checkbox 424 displays die path of messages that have been passed to selected objects during a Runtime execution, such objects having been selected by the au ior dirough die structure view window 330. First, one sees a message 425 sent, specifying the sender 423, me message type 422 and the recipient 421. What follows is the chain of messages mat arise from message 425. For example, message 426 caused, in particular, a chain to occur with received messages 427. Turn knobs 428a, 428b, 428c, 428d, 428e and 428f allow the corresponding message lines to be revealed or hidden, thereby allowing die author to concentrate on the area of interest. More refined embodiments could easily include other standard debugging features, such as breakpoints, stepped execution and examination of selected data, as are well known in the art. h. mToon Editor. An mToon is a continuous series of images compiled by die system into a single file. Any animation files created in a 3D program, or in a 2D animation 45 program which has been saved as or converted to PICT or PICS files, can be imported to the mToon Editor 53 and processed as an mToon. mToons are eel-based and very flexible. In addition to being able to specify die playback rate and duration of an mToon, a selected eel or range of eels in the mToon can be specified for playback. These ranges can be dynamically set during Runtime, opening new creative possibilities to the multimedia author. For example, the sitting, walking, and running motions of a rabbit can be compiled into a single mToon linked to an Element. During Runtime, Messengers or the Miniscript Modifier can be used to specify which eels of the animation to play back according to predefined conditions. Thus, mToons absϋ-act physical action with frame-by-frame control. The system maintains a link to the actual picture images that make up the individual frames of the mToon. Thus, if any of these images is updated, as verified by the system through the modification date, the system asks the user whether the mToon should be recreated widi die new images. This "hot link" feature is ideal when additions or adjustments are made frequently to individual frames. Audiors can import single or multiple PICS or PICT files into the mToon Editor, and then edit, compress and save them as an mToon. Authors also can open and edit existing mToons in this window. Moreover, audiors can define ranges of eels widiin each animation and name them as a subset of die mToon. In the current embodiment, diese eel ranges are a sequential range of integers; however, diere is nouiing to preclude eel ranges from being completely discontiguous and in any order. Once defined, authors can access diese ranges by name via Messengers or Miniscript Modifiers during Runtime. 46 EET RUL£26) With reference to Figs. 9(a)-(d), the operation of mToon editor 53 is shown. In Fig. 9(a), mToon editor window 900 is shown, having a registration point 901 which establishes the upper left corner of an inserted animation eel, a eel number field 902 which shows die number of die current eel, and a selection field 903 which displays the range of eels selected for editing. It has an mToon conu-oller 904, which is used to preview the animation (which may assist the author in selecting a range of eels for editing), and has step buttons to step forward or backwards through the animation, eel by eel. Finally "show" pop-up menu 905 allows die audior to select a specific range of eels, referenced by name to be played. In Fig. 9(b), the mToon source file information dialog 910 is shown. Thus, die file path 911 is displayed, along widi the eel numbers 912, the original file names for the eel contents 913, the index number 914, if any, when die eel is a PICS file, and the file format 915 (e.g. PICT, PICS). In Fig. 9(c), the compression settings dialog 920 is shown. The compression type pop-up menu 921 specifies the compression method to be used (e.g., none, Animation, Cinepak, Graphics, Photo-JPEG, or Video). The color depth pop-up menu 922 sets the number of colors used by an mToon, which defaults to 256. A "random access" checkbox 923 provides authors with random access to individual eels despite compression. This is necessary for an mToon to be played backwards or forwards, eel by eel, or at a constant speed. The compression quality slider 926 controls the quality of die chosen compression method, widi lower quality imparting artifacts into the mToon. In Fig. 9(d), die ranges dialog 930 is shown. It permits the naming of sequences of eels, so that they may be accessed by name, as for example, by the Miniscript Modifier. The name field 931 shows the name assigned to die range; the start field 932 shows the eel number at me start of the range; the end field 933 shows the end; the delete button 934 allows a selected (highlighted) range to be deleted; and die "new" button allows a new range to be created. i. Modifier Palettes. With further reference to Fig. 2, modifier palettes 35a and 35b are shown. As discussed below, the system's extensible architecture enables programmers to create and insert additional Modifiers into the system, possibly necessitating additional modifier palettes. Each entry in a modifier palette allows an instance of a Modifier to be created and incorporated widiin (i.e. , linked to die instance of a particular Element (Element, Scene, etc.) through a simple click, drag and drop procedure. Modifier palettes 35a and 35b include (as discussed in greater detail below) icons for the behavior 340, the miniscript Modifier 1980, the MESSENGERS [(basic) 1200, if messenger 1220, timer 1240, border detection 1260, collision 1280, hypertext 1300 (at bottom right) and keyboard 1320]; the VARIABLES [integer 1000, integer range 1020, vector 1040, boolean 1060, string 1080, floating point 1100, point 1120 and time 1140]; the SCENE MODIFIERS [change Scene 1400, return 1420 and Scene transition 1440]; the MOTION MODIFIERS [simple 1600, drag 1620, path 1640 and vector 1660]; the VISUAL MODIFIERS [graphic 1700, color table 1720, gradient 1740 and image effect 1760]; the SOUND MODIFIERS [sound effect 1800 and audio fade 1820]; the style modifier 1900, and the cursor modifier 1920. The classification Modifier 1940 (Fig. 22) and set value Modifier 1960 (Fig. 23) are not shown. j. Drag and Drop. As will be discussed below, files containing code for Components (Modifiers and Services) may be added freely to die system by dragging and dropping diem inside a special resource folder just as easily as instantiated 48 STITUTE SHEET RULf 26 Modifiers are dragged and dropped into Projects. As discussed herein, Elements and Modifiers may be freely dragged from window to window widiin a Project, or into libraries or other Projects. 5. Object Messaging. The object messaging mechanism is integrated into the system so as to be accessible to authors via d e configuration of Modifiers. Authors can use mis mechanism to specify the manner in which dieir Elements and Modifiers will communicate with one another. As is discussed in greater detail in the next section, audiors can configure dieir Modifiers in Edit Mode to perform actions in response to messages received during Runtime Mode. These messages are created and sent eidier by the system itself or by a special type of Modifier known as a "Messenger" (i.e., any Modifier capable of sending a message). For example, during Edit Mode, an audior could configure the simple Messenger Modifier 1200 depicted in Fig. 13(a) to respond to a "Mouse Up" message 1203. This message typically would be sent by the system during Runtime Mode when the user clicks on the Element containing this Messenger Modifier 1200. By configuring pop-up menu 1204 with a "Hide" message (a type of message known as a "Command," discussed below), die audior will cause Messenger Modifier 1200 to respond to the "Mouse Up" message during Runtime Mode by sending die "Hide" Command to the Element, which in turn will cause the Element to hide itself from view. Thus, when the user clicks on the Element during Runtime Mode, it will disappear. a. Categories of Messages. 49 In one embodiment, there are diree general categories of messages from which audiors can select to configure dieir Modifiers: (i) "Author Messages: (ii) "Environment Messages:" and (iii) "Commands." Audiors can configure dieir non- Variable Modifiers to respond to diese messages by performing a particular action. Some Modifiers respond by triggering a single performance of an action (e.g., send a message), whereas others respond by enabling or disabling a continuous action (e.g., start or stop motion). Numerous odier variations are possible when creating a Modifier via the Component API, as discussed in greater detail below widi respect to die system's implementation. (1) Author Messages. Audior Messages are messages created by an audior and sent from a Messenger for the purpose of enabling, disabling or triggering other Modifiers. Audiors can provide mnemonic names describing the purpose of a message, which typically is to notify other Modifiers that a particular "event" has occurred or diat a particular "action" is desired. It should be noted diat reusability is enhanced to the extent the author specifies general "events," as opposed to desired "actions," as this makes fewer assumptions regarding die destination Modifier. For example, a message indicating that a "collision", occurred is more likely to be reusable man one requesting the destination Modifier to "beep." Some authors, however, may prefer more specific message names and be willing to sacrifice some degree of reusability. As discussed below, Audior Messages are (by default) "broadcast" from their specified destination down die Structural and Behavioral Hierarchies. This Hierarchical Message Broadcasting mechanism, as noted above, significantly 1822 PCI7US96/04496 enhances the reusability of Elements and Behaviors. This mechanism is discussed in greater detail below. Authors can create and name Author Messages eidier from a special Messenger pop-up menu (described below) or from a dialog box generated by a menu item selected in Edit Mode. In either event, audiors can provide mnemonic names describing the purpose of a message. In addition to using the dialog box to create and name Author Messages, audiors also can use this dialog box to create and name message "groups" and rearrange their Audior Messages among these groups. By organizing Author Messages in this manner, authors can select an Author Message from an organized hierarchical list integrated into the Messenger pop-up menu. As a result, authors can limit their view to die particular Author Messages widiin any one group, diereby simplifying die audioring process. Other embodiments include multiple levels of "sub-groups" and "one-to-many" and "many-to-many" relationships between Author Messages and groups/sub-groups. (2) Environment Messages. Environment Messages are messages created and sent by the system to reflect changes in the state of the runtime environment, whether due to user events (e.g. , depressing the mouse or a key on the keyboard), application events (e.g., a Scene change) or odier internal state changes detected by the system (e.g., the "enabling" by the system of an object container). Upon detecting such an "environment event," the system sends an Environment Message to the appropriate Element in die Structural Hierarchy (e.g., "Mouse Up" to die Element clicked on by the user, or "Project Started" to the Project upon activation of the Project during Runtime Mode). 51 That message is then broadcast in a limited fashion solely to the Behaviors and odier Modifiers widiin diat destination Element. In other words, the message does not "cascade" to any child Elements contained widiin diat destination Element, as described in greater detail below. Thus, such messages are broadcast down die Element's Behavioral Hierarchy, but not its Structural Hierarchy. Audiors also can configure a Messenger to send Environment Messages to any destination, even though the actual environment event represented by die Environment Message never occurred. In other words, die system provides audiors with a mechanism to "fake" or simulate the occurrence of environment events. For example, a "button" Element might contain a Modifier d at emits a "click" sound when pressed (i.e., when the user releases die mouse button on that Element and the system sends a "Mouse Up" Environment Message to that Element). The audior might want to simulate a user's mouse click in another situation (e.g., in an animated help screen showing the user how to activate diat Element). By configuring a Messenger to send a "Mouse Up" Environment Message to the "button" Element at the desired time, the author can simulate mat environment event and cause die "button" Element to respond exactly as it would had die user released the mouse button on that Element. By default, Environment Messages sent by Messengers are (unlike those sent by die system) broadcast down die Structural as well as Behavioral Hierarchies. Thus, diey are sent to all Elements and Modifiers, if any, contained widiin a destination Element or Behavior. As will be discussed in greater detail below widi respect to the system's implementation, many aspects of the Runtime environment are available during Edit Mode. In this regard, the system sends certain Environment Messages (not "visible" to authors) during Edit Mode to enable audiors to see die effects of particular actions, such as setting the color and other graphic properties of an Element, widiout having to run their title. (3) Commands. A Command is a special type of message that automatically invokes one of an Element's inherent capabilities. If an Element does not have diat particular capability, or is not an appropriate state to respond, the Command is ignored. Unlike a Modifier that can be configured to respond only to particular Author or Environment messages, Elements cannot be configured to elect whedier to respond to a Command. They respond automatically upon receiving a Command. For example, a QuickTime™ movie Element inherently is capable of playing the QuickTime movie to which it is linked. Upon receiving a "Play" Command, the Element starts playing the movie. If, however, an audior sends a "Play" Command to a Text Element, the Command is ignored because Text Elements do not know how to "play" media. Similarly, a QuickTime™ movie Element that already is in its "play" state (discussed below) will ignore a "Play" Command. Commands are sent only by authors (via a Messenger pop-up menu, described below), and affect only Elements (i.e., they are ignored if sent to Modifiers). Unlike Audior and Environment Messages, Commands are never broadcast. Once die destination Element responds to the Command, die Command is "deactivated" and is not passed down die Structural or Behavioral Hierarchies. However, certain Commands cause Elements to change "state, " which in turn causes the system to generate and broadcast a related Environment Message. For example, at any given time, an animation or movie Element may be in a 53 particular state, such as "play," "stop," or "pause. " A "Play" Command from a Messenger might cause an Element to transition from a "stop" or "pause" state to a "play" state. If so, the system detects this state transition and sends a "Played" Environment Message to the Element. That Environment Message sent by the system is broadcast down only the Behavioral Hierarchy, to all Behaviors and odier Modifiers contained widiin die Element. In mis embodiment, the audior cannot "fake" Environment Messages that are generated in response to an Element's state transition. Yet, given that die audior configured a Messenger to send die Command that caused the system to generate this Environment Message, the "event" (i.e. , die Element's execution of the Command) actually occurred, and therefore need not be "faked. " This state transition mechanism is described in greater detail below with respect to die system's implementation. b. Parts of a Message. As noted above, messages are sent only by the system and by Messenger Modifiers. From the author's perspective, they are sent by "name" and can be received by any Modifier configured to respond to diat name. When configuring a Messenger to send a message, the audior also specifies a destination for die message and (optionally) some data to be sent along widi the message. In addition, die audior can alter a message's path after reaching its targeted destination (e.g. , by restricting the broadcasting of an Audior Message to the initial destination Element and its Modifiers). These various parts of a message are described below in the context of the Messenger pop-up menus mat are available to all Messengers. The data structures and other implementation details regarding these parts of a message are described in greater detail below widi respect to die system's implementation. (1) Message Name. All non- Variable Modifiers typically are enabled, disabled, and/or triggered in response to a message. They therefore typically include one or more "Message" pop-up menus from which the author can select die name of die particular Audior or Environment Message to which mat Modifier will respond. Message pop-up menus do not include Commands because, as noted above, only Elements respond to Commands. As is discussed in greater detail below, certain Modifiers contain multiple Message pop-up menus (e.g., one to enable an action and anodier to disable that action, or one to apply a particular effect and another to remove diat effect). The programmer that creates die Modifier has, via the Component API, a wide range of "inherited" functionality from which to choose (including as many instantiations of Message pop-up menus as is desired). When configuring a Messenger Modifier to send a message, however, the author typically will select that message from a "Message/Command " pop-up menu, which is similar to the Message pop-up menu, but also includes Commands (for sending to an Element). Typically, Messengers contain only one Message/Command pop-up menu for sending a single message. If multiple messages must be sent, the author simply can create a second Messenger that responds to die same message. In another embodiment, however, a programmer could create a Modifier capable of sending multiple messages using the Component API discussed below. The Message and Message/Command pop-up menus are quite similar in nature, and dierefore are discussed together widi reference to Table I. From either menu, the audior can select "None" (not shown) to indicate that no message is selected (to be sent or to invoke die Modifier). In addition, the author can create or select an Audior Message from a hierarchical "Author Messages" menu item (also not shown) that lists all Audior Messages used anywhere in the Project (organized by groups, as noted above). The system maintains this list of Audior Messages and makes it available to Modifiers dynamically so that dieir Message and Message/Command pop-up menus automatically contain all Author Messages. The remaining choices include Environment Messages (from either menu) and Commands (from the Message/Command pop-up menu only). As noted above, many Commands will cause an Element to change state, resulting in the generation of an Environment Message being broadcast throughout die Element. The Message pop-up menu therefore includes diese Environment Messages in place of the corresponding Commands present in die Message/Command pop-up menu. Commands are italicized on die Message/Command pop-up menu for easy identification by die audior. For efficiency, the Environment Messages and Commands on bodi menus are illusϋ"ated together in Table I. The "Type" and "Message/Command" columns represent the two-level hierarchical nature of these menus. Commands are italicized in this table, as in the actual menus. Whenever the two menus differ, both the Environment Message (from the Message pop-up menu) and the corresponding Command (from the Message/Command pop-up menu) are shown wim a "slash" between diem. When the Message pop-up menu has no Environment Message corresponding to the Command on die Message/Command pop-up menu, die italicized Command is "greyed out" on the Message pop-up menu (not shown in mis table) to indicate that it cannot be selected by the author. TABLE I. ENVIRONMENT MESSAGES AND COMMANDS 56 Iyj2£ Message/ Command Description Mouse Mouse Down Environment Message sent in Mouse Up response to a user's mouse actions. Mouse Up Inside Mouse Up Outside Mouse Over Mouse Outside Mouse Tracking Tracked Mouse Outside Tracked Mouse Back Inside Element Shown/Show Environment Message! Command Hidden/Hide used to indicate diat an Element has been (or "command" an Element to be) concealed or revealed Selected/ Select Environment Message/ 'Command Deselected/Deselect used to indicate diat an Element's Toggle Select "selected" state has been (or "command" an Element's "selected" state to be) set or reset. Also Command to "toggle" that state Edit Element Command to Text Element to toggle Edit Done whether user allowed to enter or Update Calculated Fields edit its text, and related Environment Message to indicate that user's text editing is complete. Also Command to update calculation of value of Variables inside text fields Scroll Up Command to move content of Scroll Down Element within its frame in a Scroll Left particular direction. An Integer Scroll Right Variable determines how far to move Element content (in pixels) Preload Element Used to preload media file into RAM for optimal playback (only for PICTs, mToons and AIFF sounds) 57 ΪΪES Message/Co/πmαm/ Description Play Control Played/P/αy Environment Message/ Command Stopped/Stop used to indicate diat a movie, animation or Sound Element has been (or "command" such an Element to be) played once, leaving last cel on screen (except Sound), or stopped Play-Shown/P/αy-S jow Environment Message/ Command Stop-Hidden/Stop-H/Vfe used to indicate diat a hidden animation or still graphic has been (or "command" such an Element to be) played once/shown, leaving last cel on screen (except Sound), or stopped/hidden Paused/Λwtfe Environment Message/ Command Unpaused/£//ipa«je used to indicate diat a movie, Toggle Pause animation or Sound Element has been (or "command" such an Element to be) paused or unpaused. Also Command to toggle the "paused" state of such an Element. At First Cel/At First Cel Environment Message/ Command At Last Ce\/At Last Cel used to indicate that an mToon animation Element has reached (or "command" such an Element to reach) its first or last cel Play Forward Command used to cause movie or Play Backward animation Elements to play forwards or backwards Motion Motion Started Environment Message to indicate Motion Ended diat an Element's motion has started or ended Transition Transition Started Environment Message to indicate Transition Ended diat an Element's transition has started or ended Parent Parent Enabled Environment Message to indicate Parent Disabled diat die Modifier's parent object container has been enabled or disabled 58 Type Message/Command Description Scene Scene Started Environment Message to indicate Scene Ended that a Scene has been started, Scene Deactivated ended, deactivated or reactivated Scene Reactivated Shared Scene Returned to Scene Environment Message to indicate to Scene Changed a Shared Scene that control has Scene Time Expired returned to or changed from a No Next Scene Scene, or that time has expired No Previous Scene widiin a Scene, or diat, with respect to die current Scene, diere is no previous or next Scene Project Close Title Command to close a Project or Project Started standalone "tide" (i.e., quit User Timeout Runtime Mode) and Environment Message to indicate that a Project has started or diat die specified user timeout period has expired widiout the expected action by the user Get/Set Get/Set Height Command to read or write PICT Attribute Get /Set Position Attributes Get/ Set Width Get /Set Layer Get /Set Text Command to read or write Text Get/Set Layer Element Attributes Get/Set Height Command to read or write mToon Get /Set Position animation Element Attributes Get/ Set Width Get/ Set Layer Get/ Set Cel Get/Set Range Get/ Set Rate Get/Set Paused 59 Tvp? Message/Comment Description Get/ 'Set Height Command to read or write Get/Set Position QuickTime™ movie Element Get /Set Width Attributes Get/Set Layer Get /Set Cel Get/Set Range Get /Set Rate Get/Set Paused Get/Set keyFrame Get/Set Volume Get/Set timeValue Get/Set Rate Command to read or write Sound Get/Set Volume Element Attributes Get/Set masterVolume Command to read or write Project Get/Set User Timeout Element Attributes Marks Execute Marks Command to execute a particular Begin Marks "mark" chosen by die author, or End Marks begin or end execution of all "marks" within an AIFF-formatted soundtrack linked to a Sound Element As is illustrated in Table I above, audiors can configure dieir Modifiers to send or be invoked by a wide variety of Environment Messages and Commands (as well as create their own Audior Messages). For example, in this embodiment, audiors can select Environment Messages representing: (i) the state of users' mouse movements (e.g., "Mouse Up," "Mouse Down," "Mouse Tracking," etc.); (ii) the state of a Media Element's "playing" of media (e.g. , "Shown," "Hidden," "Paused," "Stopped," etc.) or its motion in the Scene (e.g., "Motion Started" or "Motion Ended"); (iii) die state of Structural Elements such as a Scene (e.g., "Scene Changed") or die entire Project (e.g., "Project Started"); and even (iv) the state of an Modifier's Parent object container (e.g., "Parent Enabled" or "Parent Disabled"). A wide variety of Commands also is made available to enable authors to access die inherent Attributes and capabilities of dieir Elements, including: (i) causing a Media Element to change its state of "playing" its media (e.g. , "Show," "Hide," "Pause," "Stop," etc.); (ii) causing a Text Element to toggle its "editable" state (e.g., "Edit Element") or update calculations on Variables contained in its text field (e.g., "Update Calculated Fields"); (iii) causing a Sound Element to sync to "marked" locations within its linked soundu-ack (e.g., "Execute Marks"); (iv) causing an Element to preload its linked sound or animation for optimal playback (e.g., "Preload Element"); and (v) causing an Element to read or write its various Attributes (e.g., "Get Cel" of an animation or movie, "Set Position" of any Graphic Element, "Get Master Volume" of the Project, etc.). As is apparent from the above discussion, anodier embodiment of this system could make virtually any internal state d-ansition or event known to the system available to authors as an Environment Message, as well as any additional Commands to which Elements are capable of responding. (2) Message Destination. When configuring a Messenger to send a message, authors must specify a "destination" Element or Modifier to which that message will be sent initially. As noted above (and discussed in greater detail below with respect to the message path), die message may propagate further and be "broadcast" down die Su-uctural and/or Behavioral Hierarchies. In any event, audiors specify their desired message destination by configuring dieir Messenger's Destination" pop-up menu, illusd * ated below in Table II. Using a mechanism referred to as "Relative Targeting." an audior can specify a "relative" destination in die Structural and Behavioral Hierarchies — e.g., any object container containing that Messenger, including "Project," "Section," "Subsection," "Scene," "Element's Parent" and "Messenger's Parent." This mechanism provides die author widi a significant degree of reusability of that Messenger. For example, by specifying "Parent" as the destination for a message sent by a Messenger, die audior can use that Messenger inside a different object container (i.e. , another Element or Behavior) without modification. It will always send diat message to its "Parent" object container. Audiors also can specify the "Next Element" and "Previous Element," which are siblings of die Element containing the Messenger. This too is i form of Relative Targeting, in that the destination Element is not determined precisely at authoring time. Instead, it is determined at Runtime relative to die Messenger's position in die Sϋ"uctural and Behavioral Hierarchies. Audiors also can specify certain destinations known to die system during Runtime Mode, such as d e "Active Scene," die "Shared Scene, " and die "Sender's Parent. " These too are a form of Relative Targeting, in that diese destinations are determined based upon die state of the runtime environment. An author also may employ "Direct Targeting" to select, as a message destination, particular Elements or Modifiers made available to die audior based upon die system's knowledge of die Structural and Behavioral Hierarchies (e.g., "Messenger's Siblings" or "Element's Siblings"). In this case, however, the author selects the actual name of a particular Element or Modifier, and dius targets that Element or Modifier directly. During Runtime Mode, the message will be sent to that particular Element or Modifier (provided mat the system can still locate that Element or Modifier). Both the Direct Targeting mechanism (in which the system resolves the destination name into an "ID" during Edit Mode) and the Relative Targeting 62 mechanism (in which the system resolves the destination "name" dynamically at Runtime) are described in greater detail below widi respect to the system's implementation. TABLE π. MESSAGE DESTINATIONS Destination Comments Project Message sent initially to Project Element containing Messenger Section Message sent initially to Section Element containing Messenger Subsection Message sent initially to Subsection Element containing Messenger Scene Message sent initially to Scene Element containing Messenger Element's Parent Message sent initially to Parent of Messenger's "Parent Element" Messenger's Parent Message sent initially to Messenger's Parent object container (Element or Behavior) Next Element Message sent initially to Element "next in line" (in the Structural Hierarchy) after Messenger's "Parent Element" Previous Element Message sent initially to Element "previously in line" (in the Sϋ-uctural Hierarchy) before Messenger's "Parent Element" Active Scene Message sent initially to Active Scene (visible to user at time message is sent) Shared Scene Message sent initially to Shared Scene (visible to user at time message is sent) Source's Parent Message sent initially to Parent object container of the "source" Messenger (i.e., die Messenger diat sent die message which invoked the Messenger sending this message) Messenger's Siblings Message sent initially to actual Modifier selected by (DIRECT TARGETING) name from submenu (containing Messenger's siblings) 63 Destination Comments Element's Siblings Message sent initially to actual Element selected by (DIRECT TARGETING) name from submenu (containing siblings of Messenger's "Parent Element") Parents Message sent initially to Element or Behavior (DIRECT TARGETING) selected by name from submenu (containing Messenger's ancestors) (3) Message Data. In addition to specifying the message name and destination in die Messenger's dialog box, audiors also can configure Messengers to include certain data with their message. Authors specify such data using the "With" pop-up menu, discussed below. Authors can avoid this option entirely by selecting "None" from the With pop-up menu. Audiors also can select "Enter Value" which generates a dialog box containing a field into which audiors can enter any desired value. By selecting "Incoming Value," this Messenger will "pass on" to die destination the data received with die message that invoked this Messenger. The system determines the value of such data dynamically during Runtime Mode. Finally, audiors can select any Variable shown on the Widi pop-up menu. All Variables within the Messenger's "scope" are included. As discussed above with respect to Hierarchical Variable Scoping, a Variable is accessible to all descendants of its parent object container. Thus, the Messenger can access any Variable whose parent object container also contains that Messenger. (4) Message Pad . As noted above, Audior Messages and Environment Messages sent by Messengers will, by default, be "broadcast" to all objects, if any, contained within 64 that destination Element or Modifier (i.e. , diey will propagate from the destination down bodi die Structural and Behavioral Hierarchies). The only exception is a "switchable" Behavior which, when switched off, prevents further broadcasting of a message to its child objects. As a general rule, Environment Messages sent by the system will be broadcast solely to Behaviors and odier Modifiers widiin the destination Element. Certain Environment Messages, however (e.g. , "Scene Started" and "Parent Enabled") are of sufficient interest to most Elements to merit being broadcast down from the Scene. Commands, on the odier hand, are sent initially to an Element (or else ignored) and will propagate no further. Authors can modify die default message path of the messages they send via Messengers, as discussed below. (a) Broadcasting of Messages. Hierarchical Message Broadcasting, as discussed above, involves die ϋ-aversal of the Sϋ-uctural and Behavioral Hierarchies in an order determined by die order of die objects as represented in die Sϋ-ucture View Window (see, e.g. , Structure View Window 330 in Fig. 2), initially determined by the order in which such objects were created. Authors can modify this order by "dragging and dropping" icons widiin die Structure View Window 330. For example, die message is broadcast first down die Behavioral Hierarchy of die Element or Behavior object container — i.e., to all child Behaviors and other Modifiers of that Element or Behavior. By default, it is sent from Modifier to Modifier widiin die Behavioral Hierarchy. At any given level, die order is determined, as noted above, by the order in die Structure Window. Upon reaching a Behavior, it is sent down to the child Behaviors and other Modifiers contained within that Behavior. Upon reaching a non-Behavior Modifier, it is sent to a sibling Behavior or other Modifier (if any), and so on. Even if a particular Modifier responds to die message, die message is "relayed" to the next Modifier 65 in the Behavioral Hierarchy until all Modifiers widiin the original Element or Behavior object container have received the message. Of course, if the original destination was a non-Behavior Modifier, no further propagation of die message would occur. Yet, if die original destination was an Element, die message would, by default, "cascade" down die Su-uctural Hierarchy to the child Elements contained widiin that Element. The message would be sent down die Behavioral Hierarchy of each such child Element as discussed above, and dien propagate to the next child Element until all Elements (and objects contained widiin them) widiin die original Element object cor.tainer have received die message. Thus, as noted above, Audior and Environment Messages sent by Messengers are, by default, broadcast down both the Structural and Behavioral Hierarchies. Audiors may, however, configure a Messenger to limit or optimize this default padi to avoid unnecessary (and perhaps undesired) message ϋ-affic or otherwise minimize potential performance botdenecks. (b) Immediate. As is discussed in greater detail below widi respect to die system's implementation, messages are delivered to Elements and Modifiers in "direads" of execution during Runtime Mode. Despite the message dispatching efficiencies diat result from routing messages along the Su"uctural and Behavioral Hierarchies, an audior can impact system performance in certain situations, for example, by broadcasting a message to a large number of Elements and Modifiers. In this regard, authors are provided with an option to configure a Messenger to postpone the default "immediate" processing of the message sent by that Messenger until after die current "chain of activities" has concluded. In other words, rather than process this message "immediately" as it is encountered, die system can complete its more time-critical tasks and wait until an "idle" cycle to process this message. (c) Cascade. Anodier mechanism provided to the audior to optimize performance is the option to configure a Messenger to limit the default broadcasting of a message sent to an Element object container to the Behavioral Hierarchy widiin that destination Element. In other words, die message will not "cascade" to child Elements within die destination Element. It will be processed in a manner similar to that of Environment Messages sent by the system. This feature will be illustrated in the snake example discussed below. (d) Relay. A final mechanism provided to die audior to optimize performance is the option to configure a Messenger to limit the default broadcasting of a message to die first Modifier diat is configured to respond to that message. In other words, once a Modifier responds to the message, the message will not be "relayed" to another Modifier and will not "cascade" to anodier Element. It will just stop. 6. Object Configuration. a. Elements. Each Element is a state machine, and in die current embodiment, has six states: (i) initial (construction); (ii) begin play; (iii) play; (iv) end play; (v) duration (what to do after play); and (vi) last (desd-uction). Not all these states have any particular meaning when connected with various media. For example, for a PICT, there really only is die play state. End play might signify releasing a cached bitmap. 67 The author configures a Media Element dirough die Element configuration dialog 950 as shown in Fig. 10. Dialog 950 includes the Element title 951 and Element type icon 952 (showing that die Element is either an unlinked Graphic Element or linked to a PICT, mToon, QuickTime™ movie, Text Element, or Sound Element in AIFF or snd format), and source file path 953. There are a variety of check boxes to configure the initial state. Thus, "Hidden" checkbox 954 determines whether die Element is initially hidden at Runtime, "Paused" checkbox 955 determines whether movies, mToons and sounds are initially paused. "Loop" checkbox 959 determines whedier an mToon will continue replaying. "Back and Forth" checkbox 960 determines whether the mToon is played backwards after being played forwards (before possibly repeating itself in accordance widi "Loop" checkbox 959). "Mute" checkbox 964 determines whether a sound is initially muted. Also data entry area 963 allows one to override a sound file's original volume. Odier options are configured dirough die "Play Every Frame" checkbox 956 (which overrides QuickTime's feature of dropping frames to ensure sound synchronization), die "Cache Bitmap" checkbox 957 (which converts the Element's screen display format to a bitmap, obviating the need to perform the complex instructions which created such display) and the "Direct to Screen" checkbox 958 which overrides layer order and draws the Element on top of all others. Finally, die data entry area 962 allows the mToon rate to be adjusted and the data entry area 961 allows the layer order number to be adjusted. b. Modifiers. The primary means for "modifying" an Element's inherent characteristics is provided by Modifier configuration dialogs. As was discussed above, little or no scripting or programming is required; radier, it is a visually-driven audioring environment. Each of the Modifiers has its own configuration dialog. The types of data present in such dialogs reflect the information required to properly configure die modifier. Thus, it is useful to understand how to "program" the Modifiers - Behaviors, Variables and Capabilities. (1) Behavior. The Behavior, by containing additional Behaviors and odier Modifiers, acts as the structural backbone of die Behavioral Hierarchy. As such, die Behavior view 34 produces, widi reference to Fig. 11, a dialog box 340 to configure and display various data items thereof. The Behavior dialog box 340 includes a name field 343, a modifier icon 344, an "enable when" pop-up menu 345 for specifying an enabling message, and a "disable when" pop-up menu 346 for specifying a disabling message. Also included are a "clean up" button 341, a switch check box 342, a set of message lines 347a, 347b, 347c, 347d, as well as a set of contained Modifiers 348a, 348b, 348c, 348d, 348e. The switch check box 342 is used to allow an author to enable and disable the Behavior via the enable and disable pop- up menus 345 and 346. The enabling and disabling messages thus specify an operational "window" for the Behavior. The name field 343 can represent, as a mnemonic aid, the Behavior's conceptual function (e.g. , "steering" Behavior). The Modifier icon 344 represents the Modifier type (in this case, Behavior). Each of the contained Modifiers 348a, 348b, 348c, 348d, 348e are represented by dieir name, icon and 69 ordinal number (the number in parentheses), which is the order in which each of the Modifiers is executed within the Behavior. By default, diese ordinal numbers are the creation order of d e contained Modifier, but can be overridden by a special pop-up menu (not shown). These Modifiers may be rearranged around the dialog box 340 by clicking and dragging. The "clean up" button 341 serves to automatically rearrange the contained Modifiers according to their messaging order. The message lines 347a, 347b, 347c and 347d represent the messages to and from the contained Modifiers 348a, 348b, 348c, 348d, 348e. Thus, for example, Modifier 348d is enabled by the mouse tracking message 347a, represented by the vertical arrow pointing to the Modifier, and sends an update Element message 347d, represented by the vertical arrow pointing to die message line. In the embodiment discussed here, a purple arrow is used to represent a message emanating from a contained Modifier, a green arrow is used to represent a message received by a contained Modifier diat executes, applies or enables diat Modifier, and a red arrow is used to represent a message received by a contained Modifier that terminates, removes or disables diat Modifier. Thus, in this example, one can see mat messenger modifiers 348c and 348d are each responsible for creating die "Update Element" message 347d, which serves to enable Miniscript Modifier "Calculate Element Specs" 348e. (2) Variables. Variable Modifiers store values, such as numbers and sϋ * ings. These values can be configured to act as variables (changeable values) or constants (non-changeable values). These values may be referenced by Messengers and sent widi messages. In addition, audiors can write scripts using the Miniscript Modifier to reference and modify diese values as well as include diem widi messages. 70 The location of a Variable within die Structural and Behavioral Hierarchies determines its scope; that is die group of objects which can access that Variable. Put simply, a Variable is accessible to all descendants of its parent. For example, a Variable placed on a Section is available to any Modifier on the Section, and all other descendants of diat Section. A Variable whose parent is die Project is called a global. Global Variables can be accessed by any appropriate Modifier in die entire Project. A "special- purpose" scope may be created through aliasing, as was discussed above. Variables are eidier simple or compound. Simple Variables store a single value, whereas compound Variables store at least two values. For example, an integer Variable stores a single integer, so it is a simple Variable. On e other hand, a point Variable stores two values (die x and y coordinates), so it is a compound Variable. With reference to Figs. 12(a)-(h), the dialog boxes for the various Variable Modifiers (integer 1000, integer range 1020, vector 1040, boolean 1060, string 1080, floating point 1100, point 1120 and time 1140) each respectively includes a title 1001, 1021, 1041, 1061, 1081, 1101, 1121, 1141; icon 1002, 1022, 1042, 1062, 1082, 1102, 1122, 1142; "Cancel" button 1004, 1024, 1044, 1064, 1084, 1104, 1124, 1144; and "OK" button 1005, 1025, 1045, 1065, 1085, 1105, 1125, 1145. The "Cancel" button is used to discard any editing changes, while die "OK" button commits such changes to memory. (a) Integer. An Integer Variable is used to store an integer value (e.g., 7). Integer Variables range in value from -32767 to 32767. In Fig. 12(a), one can see a data entry area 1003 comprising an entry position for an integer. 71 (b) Integer Range. An Integer Range Variable is used to store an integer range value (e.g. , 4...8). In Fig. 12(b), one can see a data entry area 1023 comprising an entry position for two integers, the starting integer of the range and die ending integer of die range. (c) Vector. A Vector Variable is used to store vector values in degrees (angle) and inches per second (magnitude). In Fig. 12(c), one can see a data entry area 1043 comprising an entry position for an angle, and one for a magnitude. (d) Boolean. A Boolean Variable stores a true/false value; In Fig. 12(d), one can see a data entry area 1063 comprising two radio buttons, one for true and one for false. (e) String. A String Variable stores a string (e.g. , "Bob Brown"). In Fig. 12(e), one can see a data entry area 1083 comprising an entry position for a string of up to 255 characters. (f) Floating Point. A Floating Point Variable stores a floating point value (e.g. , 3.14159). In Fig. 12(f), one can see a data entry area 1103 comprising an entry position for a floating point number. (g) Point. A Point Variable stores point values (e.g., (25,45)). In Fig. 12(g), one can see a data enu-y area 1123 comprising an entry position for two integers, the x- coordinate of die point and the y-coordinate of me point. (h) Time. A Time Variable stores time in the format: "minutes: seconds. milliseconds. " In Fig. 12(h) one can see a data entry area 1083 comprising an entry position for the time in such format. (3) Capabilities. As noted above, Capabilities are modifiers diat perform actions on behalf of the Element. In the current embodiment, mat would include Messengers and Effects, as well as three singletons: die Miniscript Modifier, die Classification Modifier and the Set Value Modifier. (a) Messengers. Messengers are used to send messages and (optionally) accompanying data to Elements and Modifiers. They can be enabled, disabled and triggered upon receipt of messages as can all odier non- Variable Modifiers. Aldiough each has unique functionality, there are some similarities among diem wordi noting. With reference to Figs. 13(a)-(g), one notes that die dialog boxes for die various Messengers [(basic) 1200, if messenger 1220, timer 1240, border detection 1260, collision 1280, hypertext 1300 and keyboard 1320] each respectively has a title 1201, 1221, 1241, 1261, 1281, 1301 and 1321, an icon 1202, 1222, 1242, 1262, 1282, 1302 and 1322, a "Cancel" button 1207, 1228, 1250, 1273, 1296, 73 1312 and 1331, and an "OK" button 1208, 1229, 1251, 1274, 1297, 1313 and 1332. As Messengers, each respectively has a messaging block comprising (i) a Message/Command pop-up menu 1204, 1225, 1247, 1268, 1288, 1306 and 1325, (ii) a With pop-up menu 1206, 1226, 1249, 1275, 1289, 1307 and 1327, and (iii) a Destination pop-up menu 1205, 1227, 1248, 1269, 1292, 1308 and 1326. Furdiermore, each has messaging checkboxes for (i) immediate messages 1209, 1230, 1252, 1270, 1298, 1309 and 1328, (ii) cascaded messages 1210, 1231, 1253, 1271, 1299, 1310 and 1330, and (iii) relayed messages 1211, 1232, 1254, 1272, 1279, 1311 and 1331. It is critical diat a Messenger specify die type and destination for its message. Thus, the Destination pop-up menu permits the author to designate targets in accordance widi die range of Elements specified in Table I above. The Message/Command pop-up menu allows die user to specify the type of message to be transmitted. The Widi pop-up menu permits various types of data to be attached to the message. The messaging option check boxes allow the message to be configured, respectively, for immediate ϋ-ansmission, cascading or relaying, as discussed above. Most Messengers have an "enable when" pop-up menu and a "disable when" pop-up menu, which together specify a window of events in between which the Messenger is active (and conditionally sends messages). Other Messengers have an "execute when" pop-up menu which is configured to "fire and forget, " i.e., conditionally send die message once upon receiving the triggering event. i) Basic Messenger. The Basic Messenger 1200, illustt-ated in Fig. 13(a), simply sends a message widi optional author-supplied data when a particular message is detected. 74 6 ii) If Messenger. If Messenger 1220, illustrated in Fig. 13(b), allows conditional sending of messages using Boolean logic. In addition to me "execute when" pop-up menu 1223, a data entry area 1224 allows the author to impose a condition which must be met for the message to be sent (using the same syntax as is used by die Miniscript Modifier discussed below). iii) Timer Messenger. The Timer Messenger 1240, illustrated in Fig. 13(c), waits an author- specified period of time before sending a message. One can see "execute when" 1243 and "terminate when" 1244 pop-up menus, a data entry area 1245 for expressing a countdown time in die format of "minutes: seconds. milliseconds," with a loop timer checkbox 1246 to send die timed message repeatedly. iv) Boundary Detection Messenger. The Boundary Detection Messenger 1260, illustrated in Fig. 13(d), detects collisions widi enclosures. One can see "enable when" 1263 and "disable when" 1264 pop-up menus, and diree radio buttons to specify die detection conditions for collisions with the Element's parent's borders: (i) on first detection only 1265, (ii) while continually detected 1266, and (iii) while exiting enclosure only 1267. v) Collision Messenger. The Collision Messenger 1280, illustrated in Fig. 13(e), detects collisions with Elements. One can see "enable when" 1283 and "disable when" 1284 pop-up menus. The "collide widi" pop-up menu 1285 can be used to designate Elements mat can be collided with, e.g. , Elements which are "solid. " This can be specified using the Classification Modifier, described below. The detect "in front" and 75 "behind" check boxes 1286 and 1287 can be used to filter out Elements from different layers. The detect buttons 1293, 1294, and 1295 can be used, respectively, to configure messaging only upon first contact of the Elements; continually while two Elements are in contact; or when the two Elements cease being in contact with each odier. Collisions suggest a special target for a message, apart from the normal range of targets provided dirough destination pop¬ up menu 1292 discussed above, namely die actual Elements collided widi. This is made available dirough die "Collision Elements" destination button 1290, which allows the author to toggle between the normal mode of messaging to a specified destination, and this special mode of targeting only collided Elements. The first Element collided widi may be specified exclusively dirough the use of die "First Element Only" checkbox 1291. vi) Hypertext Messenger. Hypertext Messenger 1300, illustrated in Fig. 13(f), links the sending of a message with a user's mouse actions. When a Hypertext Messenger is dropped into a Text Element, any hypertext label that has been assigned to text widiin die Element appears on the "On" pop-up menu 1303. The Messenger will us trigger upon receipt of the specified message, indicating a user's mouse action on such "hot" text. Fur ermore, through die highlight effect pop-up menu 1304, the following effects to the "hot" text may be applied: none, underline, invert, highlight, tone up, tone down or squiggly underline. This effect may be sustained through application of the "Remain highlighted" checkbox 1305. vii) Keyboard Messenger. Keyboard Messenger 1320 detects and responds to keyboard events. Instead of being triggered upon receipt of a message (as are most non- Variable Modifiers), it is triggered by author-specified (via conn-ols 1323) user key or key combinations, including die control, command, option and shift keys. The key 76 state of the trigger may be specified through radio buttons 1324 as down, up or repeating. (b) Effects. In general. Modifiers grouped under die category of Effects modify the visible characteristics of their parent Elements. With reference to Figs. 14(a)-(c), 16(a)-(d), 17(a)-(d), 18(a)-(b), 19 and 20, die categories of effects include: the Scene Modifiers (change Scene 1400, return 1420 and Scene transition 1440); die Motion Modifiers (simple 1600, drag 1620, padi 1640 and vector 1660); the Visual Modifiers (graphic 1700, color table 1720, gradient 1740 and image effect 1760); die Sound Modifiers (sound effect 1800 and audio fade 1820); the style Modifier 1900, and the cursor modifier 1920. These Modifiers respectively have a tide 1401, 1421, 1441, 1601, 1621, 1641, 1661, 1701, 1721, 1741, 1761, 1801, 1821, 1901 and 1921 and an icon 1402, 1422, 1442, 1602, 1622, 1642, 1662, 1702, 1722, 1742, 1762, 1802, 1822, 1902 and 1922. All but the path Modifier 1640 and Graphic Modifier 1700 have, respectively, a "Cancel" button 1409, 1424, 1449, 1609, 1628, 1666, 1726, 1747, 1769, 1807, 1827, 1911 and 1926 and an "OK" button 1410, 1425, 1450, 1610, 1629, 1667, 1727, 1748, 1770, 1808, 1828, 1912 and 1927. i) Scene. Widi reference to Fig. 14(a), die Change Scene Modifier 1400 is used to change the currently visible Scene during Runtime (me "Active Scene") from one Scene to another. It is executed when die message specified in pop-up menu 1403 is received. Radio buttons 1404 designate diat d e Active Scene should be switched to: (i) die next Scene in die Subsection, (ii) die previous Scene in the Subsection, or (iii) a particular Scene. When die last radio button of 1404 has been selected, pop-up menus 1405 allow the particular Section, Subsection and Scene to be specified. Checkbox 1406 allows die Active Scene to be mixed in with die destination Scene, dirough pop-up menus 1405. Checkbox 1407 adds this Scene to the "return list" of a future Scene with a return Modifier, as discussed below. Checkbox 1408 designates diat switching to a previous or next Scene will wrap around, if necessary, through die Scenes of die Subsection. Widi reference to Fig. 14(b), the Return Modifier 1420 works in association with a Change Scene Modifier widi its "add to return list" option selected. The Return Modifier returns to the Scene which has been added to die return list when die message specified in pop-up menu 1423 is received. The operation of the "Return list" using Scene change and return Modifiers is illustrated in Fig. 15. Therein, Scene A 1500, Scene B 1510, Scene C 1520, Scene D 1530 and Scene E 1540 each includes, respectively, Scene Change Modifiers 1505, 1515, 1525, 1535 and Return Modifier 1545. Scene Change Modifier 1515 on Scene B 1510 has its "Add to return list" checkbox 1407 set. Thus, when Return Modifier 1545 is executed, die Active Scene changes from Scene E 1540 to Scene B 1510, skipping intermediate Scene D 1530 and Scene C 1520. With reference to Fig. 14(c), Scene Transition Modifier 1440 creates one of a variety of transitions for a change of Scene. Upon receiving the messages set dirough pop-up menus 1443 and 1444, respectively, die Modifier in essence, registers (and revokes regisϋ-ation of) the selected transition with the system (to take effect upon an actual change of Scene). The type of transition is specified dirough pop-up menu 1445, and includes pattern dissolve, random dissolve, fade, push, slide, wipe or zoom. The number of steps required to accomplish this transition is specified dirough data entry area 1447. Certain transition effects specified through pop-up menu 1445 require further specification of a direction, which is accomplished dirough pop-up menu 1446. The rate at which the transition takes place, in steps per second, is entered through data entry area 1448. 78 ii) Motion. With reference to Fig. 16(a), the Simple Motion Modifier 1600 initiates a simple motion path. It commences and terminates execution of such motion when e messages set dirough pop-up menus 1603 and 1604, respectively, are received. The types of motion available are set through pop-up menu 1605 and include: (i) "Into Scene" which moves the Element into the Scene from its current position; (ii) "Out of Scene" which moves the Element off die Scene from its current position; and (iii) "Random Bounce" which bounces die object at random angles within die boundary of its parent Element. Direction in the first two instances of motion is specified dirough pop-up menu 1606. The number of steps and rate to accomplish this motion path are specified dirough pop-up menus 1607 and 1608, respectively. With reference to Fig. 16(b), the Drag Motion Modifier 1620 allows the user to drag die Element at Runtime. [All Media Elements have this capability during Edit Mode in die layout view window 320.] This feature is respectively enabled and disabled when die messages set through pop-up menus 1623 and 1624, respectively, are received. A checkbox 1625 controls whether the Element will be constrained to remain within die boundaries of its parent. A set of data entry areas 1626 designate die top, bottom, left and right constraints. A set of radio buttons 1627 designate whedier dragging is unconstrained, or constrained to the horizontal or vertical directions. With reference to Fig. 16(c), die Path Motion Modifier 1640 controls the motion paths of Elements, and in particular animations. It commences and terminates execution of such motion when die messages set dirough pop-up menus 1643 and 1644, respectively, are received. The editing buttons 1645 allow the author to set down a polygonal padi for the Element to follow, the padi being followed by the upper left hand corner of the Element's enclosure. Data entry area 1647 allows the position in die padi to be specified, with data entry area 1648 indicating the corresponding mToon cel which should be played at that position. Slider control 1646 allows an audior to step or play dirough die positions, forward or backwards, thus providing a previewing capability while the dialog box 1640 is open. The rate at which the animation is played over the padi is configured dirough data entry 1649. The author also can specify whedier die animation will always begin at the first position set (through radio button 1650) or whether it will continue from its then-current Runtime position (dirough radio button 1651). Checkboxes 1652, 1653 and 1654 respectively control whether the animation is to be looped indefinitely, repeated forwards and then backwards, or just played backwards. Widi reference to Fig. 16(d), the Vector Motion Modifier 1660 initiates vector motion in degrees and inches per second. It commences and terminates execution of such motion when the messages set dirough pop-up menus 1663 and 1664, respectively, are received. The actual vector for the motion is specified through pop-up menu 1665. iii) Visual. Widi reference to Fig. 17(a), the Graphic Modifier 1700 modifies graphic attributes of Elements. It is applied and removed when the messages set through pop-up menus 1703 and 1704, respectively, are received. The type of ink effect (copy, background transparent, invisible, blend, transparent, ghost, reverse copy, reverse transparent, reverse ghost, chameleon dark, chameleon light) is specified through pop-up menu 1705. A matte may be applied dirough pop-up menu 1706 widi Graphic Elements having a solid background color, such matte function making the specified color transparent. This matting color is specified through matte color box 1709, which brings up a color palette. The "hot" region shape of an Element, i.e., mat portion of an Element that will respond to mouse messages, is configured dirough pop-up menu 1707, and includes rectangle, round rectangle, oval, star and polygon. A polygon requires use of tools 1710 to create and edit 80 the end points thereof. The background and foreground colors of die Element can be selected through boxes 1708, which bring up color palettes. The border size of a defined Element shape, the shadow and shadow of die matte can be adjusted dirough data entry areas 1711, 1713 and 1714, respectively. Widi reference to Fig. 17(b), the Color Table Modifier 1720 manages color tables. It is applied and removed when the messages set through pop-up menus 1723 and 1724, respectively, are received. The color table is specified dirough pop-up menu 1725. Widi reference to Fig. 17(c), the Gradient Modifier 1740 creates color gradients in Elements that have not been linked to an external media file. It is applied and removed when die messages set dirough pop-up menus 1743 and 1744, respectively, are received. The gradient style buttons 1745 specify die direction or type of gradient (e.g. vertical, horizontal, diagonal, cenn-al). The Start and End color boxes 1746 specify the colors which comprise the beginning and end of die color gradient, accessible dirough pop-up color palettes. Widi reference to Fig. 17(d), the Image Effect Modifier 1760 creates image effects, particularly useful for implementing buttons within a project. It is applied and removed when the messages set through pop-up menus 1763 and 1764, respectively, are received. The image effect is designated dirough pop-up menu 1765 (e.g. invert, select bevel, unselect bevel, tone up, tone down). The widdi of bevel effects is specified through data entry area 1766. Tone amount is specified dirough data entry area 1767. The checkbox 1768 controls whedier image effects operate outside any margins set by a graphic modifier, as discussed above. iv) Sound. With reference to Fig. 18(a), the Sound Modifier 1800 plays sound effects. It commences and terminates execution of such sound effect when die messages set through pop-up menus 1803 and 1804, respectively, are received. The actual sound is specified dirough pop-up menu 1805, with a preview capability provided dirough button 1806. With reference to Fig. 18(b), Sound Fade Modifier 1820 decreases or increases die default volume level of a sound. It commences and terminates execution of such sound effect when the messages set through pop-up menus 1823 and 1824, respectively, are received. The percentage of the sound fading is specified dirough data entry area 1825, while the duration of die fade is specified dirough data entry area 1826. v) Text. With reference to Fig. 19, die Style Modifier 1900 is used to modify text styles. It is applied and removed when die messages set through pop-up menus 1903 and 1904, respectively, are received. The font type, alignment and size are specified through pop-up menus 1905, 1906 and 1907, respectively. The font style (e.g. , bold, italics, underline, oudine, shadow, condensed and extended) is specified dirough checkboxes 1910. vi) Cursor. Widi reference to Fig. 20, die Cursor Modifier 1920 is used to change die mouse cursor icon. It is applied and removed when the messages set through pop¬ up menus 1923 and 1924, respectively, are received. The type of cursor is specified dirough pop-up menu 1925. (c) Miniscript. The Miniscript Modifier bears special mention. Although die current embodiment emphasizes a visually-driven audioring environment, mere are times when authoring a short script is more convenient than programming a special- purpose modifier. At some point, however, frequently used constructs suggest the creation of a separate modifier. The "If" Messenger is a good example. It is used to trigger a message on a simple boolean expression handled much like die Miniscript Modifier, but with die special messaging mechanisms presented like any odier Messenger. In die current embodiment, die Miniscript Modifier allows access to internal Attributes of Elements (e.g. position) not otherwise accessible directly by audiors. With reference to Fig. 21, the Miniscript Modifier 1980 has a title 1981 and an icon 1982. It is executed upon receipt of a message as configured via pop¬ up menu 1983. The data entry area 1984 permits the audior to enter die script using the Miniscript scripting language. The compile button 1982 compiles any changes made in d e data entry area 1984. The syntax of the Miniscript Modifier is based on the following keywords: (i) "set", "of" and "to" (used to set Variables); (ii) "if" , "then", "else" and "end if" (to form conditional structures); and (iii) "send" and "widi" (for message dispatching). The Miniscript Modifier also can access and manipulate die inherent Attributes of Elements, e.g., for an mToon, its height, position, widdi, cel, range, rate and paused fields. It permits Relative Targeting of messages through tag names, such as Project, Section, Scene, Element, Element's Parent, activeScene, sharedScene and parent. The Miniscript language also has access to various mathematical functions, such as absolute value (abs), arctangent (atn), random (rnd), and so on. 83 ULI26 The Miniscript Modifier in the current embodiment is not implemented as a p-code (interpreted pseudocode) system; radier, it is a compiled, atom-based execution system. Thus, the miniscript is broken down into atoms, allowing me arguments for each to be loaded and executed by calling die appropriate function, which in most cases is die mediod of anodier Modifier. Implementations of scripting languages are well known in the art. Moreover, additional scripting functionality could be added to the system via the Component API, discussed below widi respect to die system's implementation. (d) Classification. Widi reference to Fig. 22, die Classification Modifier 1940 establishes a classification scheme which allows audiors to create and name classes and group any objects into one or more of these classes. In one sense, the Classification Modifier 1940 implements a sgt-based, rather dian a family-based hierarchy. In odier words, one can target sets of Elements, rather than families. However, as can be readily understood, die current embodiment is optimized to service a family hierarchy. The Classification Modifier 1940 has a title 1941 and an icon 1942. It is applied and removed when die messages set through pop-up menus 1943 and 1945, respectively, are received. The classification is specified through pop-up menu 1944. An example application of the Classification Modifier 1940 is in conjunction widi die Collision Messenger 1280 (see Fig. 13(e)). The Collision Messenger's "Collide With" pop-up menu 1285 can be configured to "Parent's Class, " meaning mat its parent Element will detect collisions only widi other Elements in the same class. Thus, audiors could configure bouncing ball Elements that would only bounce off one anodier. 84 (e) Set Value Modifier. Widi reference to Fig. 23, the Set Value Modifier 1960 is used to reset die value of a Variable Modifier. It has a title 1961 and an icon 1962. It is executed upon receipt of die message specified via pop-up menu 1963. The audior can select the source of the data to be written via pop-up menu 1965, and the target Variable or incoming data to be changed via pop-up menu 1964. B. Core System Architecture. The overall architecture of a system 100 embodying me principles of the invention is presented in Fig. 24. The major modules of system 100 are separated into those governing the actual title content, Runtime functionality, and Edit Mode functionality. This system 100 interacts through hardware peripherals, such as a display 3, speakers 4, keyboard 5, and mouse 6 or other joystick-like apparatus. As shown by me stretched rectangles, there are modules which straddle die Runtime/Edit Mode boundary, and are dius present in bodi. Under the classification of "title content" are those modules that are specific to a particular title. They include the logic 1, which is the storage for the project itself, including all Elements and Modifiers, and die media 2, which is the storage for all media linked into the project. There is certain functionality available to die audior only in Edit Mode, such as access to windows, dialogs, etc. However, diere is very little difference between Edit Mode and Runtime Mode in die current embodiment. In bom modes, certain background Environment Messages (not visible to the author) are issued by system 100, which trigger Modifiers to perform certain functions, such as updating Element positions on-screen. Certain functionality accessible to authors dirough Modifiers also is realized during Edit Mode. For example, the 85 system updates an Element's graphic attributes in accordance widi the audior's configuration of die Graphic Modifier, and steps dirough an audior-specified path, configured via die Padi Motion Modifier. Most Runtime functionality, however (such as die sending of messages throughout the Structural and Behavioral Hierarchies to trigger Modifiers), is suppressed during Runtime Mode. In an alternative embodiment, radier than suppressing most Runtime functionality during the Edit Mode, such Runtime functionality could proceed at a significantly slower rate. This would give die audior die impression of how die Project would proceed at normal speed, while allowing the author sufficient time to reconfigure Elements and Modifiers widiout interrupting the flow. 1. Edit Mode Functionality. The modules comprising die Edit Mode functionality in this embodiment include me title builder 51, die libraries 52, the mToon editor 53, die views manager 30 and the audioring GUI support 40, as well as the asset manager 7, the alias manager 8, the hypertext support 9 and die cross-platform architecture 50 that are shared widi the Runtime functionality. The title builder 51 is the module which transforms a project into a standalone title, severing the Edit Mode functionality. In view of die cross- platform architecture 50 discussed below, this task can be accomplished for various target platforms with minimal difficulty. The libraries 52 provide centralized storage for Elements and Modifiers, in contfast to external media resources controlled by die asset manager 7. As discussed below widi reference to Fig. 6, me libraries module 52 generates and controls the library windows 520. 86 The mToon editor 53 allows manipulation of the proprietary "mToon" animation format, as well as the conversion of other formats, such as QuickTime™, into the mToon format. As discussed above widi reference to Figs. 9(a)-(d), this module controls the mToon editor window 900, the source file dialog 910, the compression settings dialog 920 and the mToon ranges dialog 930. The views manager 30 conu-ols and presents to the author various views of die Project, which include a layers view 31, a layout view 32, a structure view 33 and a behavior view 34. The layers view 31 is used to edit projects a Subsection at a time, with die various Scenes projected along one axis, and die Elements with their layer order on the odier. It controls, with reference to Fig. 3, the layers view window 310. The layout view 32 is used to edit a Scene and is die view closest in representation to the actual running of the Project. It conϋ-ols, with reference to Fig. 2, the layout view window 320. The structure view 33 shows and allows the manipulation of the Structural Hierarchy of Project, Section, Subsection, Scenes and Media Elements, as well as me Behavioral Hierarchy of Behaviors and odier Modifiers. It controls, with reference to Fig. 4, the structure view window 330. It should be noted that Modifiers may be edited in all three views (layers view 31, layout view 32 and structure view 33), as discussed below. The Behavior view 34 shows (via Behavior Window 390 shown in Fig. 11) and allows the audior to control the messaging connections among a Behavior's child Modifiers. The asset manager 7 is a database system that provides cend-alized access to all external resources (such as pictures, animations, text and fonts) stored externally in the media 1 (e.g. on hard disk). The asset manager 7 is implemented as a flat-file database, having a search engine for files. The asset manager 7 has the ability to follow assets as they may be moved around a file system. If the asset manager 7 does not find an asset in die prescribed directory, it will first determine if odier assets that used to be in die same directory as the asset in question have been moved to anodier directory. If so, die asset manager 7 will ask me author whedier to pursue that other directory for such asset. Odierwise, it will continue to seek other "candidate" directories among the moved assets. If the asset manager 7 then fails in this process, die audior will be prompted eidier to relink die media at its new location or to link to other media, or simply ignore this lack of media linkage. In the latter case, the Element in question simply will not "play" any media. The alias manager 8 handles the aliasing of Modifiers. For Variables, such as integers, this link of data is maintained at Runtime. Thus, changes to one instance of the aliased Variable are reflected in all other such instances during Runtime Mode. In one embodiment, aliasing affects other non- Variable Modifiers only during Edit Mode. Invocation of one instance of an aliased Modifier (e.g. , in response to a message) does not result in die invocation of other such instances. However, nothing in die embodiment discussed here precludes implementing aliasing such that all Modifiers are linked dynamically, and thus are invoked simultaneously during die Runtime Mode. The hypertext support 9 implements hypertext capability, whereby any part of a Text Element's text may be transformed into a "label. " Hypertext labels are tags that can be applied to die entire text or to blocks of text within Text Elements. The authoring GUI support 40 controls various aspects of the graphical user interface, including die features of media linking 41, messaging log 42, drag and drop 43 and morphing 44. The media linking module 41 controls mapping of external media 2 resources to Elements within a Project. It also permits "thumbnails", which are draft mode, low resolution representations of such media diat are substituted for 1822 the actual media. This saves space and dius makes Projects more transportable, a useful feature during title development. Moreover, a title could even be executed over a network (e.g. , the Internet) with significant savings in bandwidm due to the replacement of large media files. The messaging log 42 provides debugging information in the form of messages sent and received by various Elements of the Project. The messaging log 42 traps all message traffic during Runtime and presents the author widi the desired filtered view diereof through die messaging log window 420 (see Fig. 8). The drag and drop module 43 provide die visual paradigm for transferring, e.g. , Elements and Modifiers from one part of a Project to another, or even to other Projects, by pressing the mouse 6 button down on me object and dragging it to its desired destination. The implementation of drag and drop behavior is well- known in die art. The consequences of particular drag and drop actions, such as Adoption, Transplantation and hierarchical object linking, are handled by particular core modules, as discussed below. The drag and drop module 43 will indicate a disallowed action by moving an outline of die object's icon back to its original position. The morphing module 44 controls the type of link to external media, thus allowing an mToon Graphic Element to be transformed into a PICT Graphic Element, for example. It does so by creating an instantiation of the new Media Element, copying over the structure pointers, ID numbers, etc. (as explained below), and setting up the appropriate icon for die new media. It does not, however, destroy die original Element until die audior performs another operation, after which "undo" capability is lost. a. Connecting Objects. As discussed in greater detail below, Elements, Modifiers, "Players" and "Assets" are implemented as classes of objects. When the audior creates an Element or Modifier, or links an Element to external media, the system 100 instantiates objects from these classes. The author may then configure and connect diese objects to form the working Project. (1) Element To Element Connection. The connection of objects underlying this authoring process is illustrated in Fig. 25. It must be stressed that die particular connections shown are for purposes of demonstration by example, and the principles underlying die present invention are not limited to die actual connections shown. One sees a portion of die Structural Hierarchy represented by Scene Element 151 pointing to its first child Element 152, which points to and is in turn pointed back to by its sibling Element 153. Both Elements 152 and 153 point back to their parent Scene Element 151. The Scene Element 151 is pointed to and points back to its parent Subsection Element 150. The Structural Hierarchy continues, though not shown, through the Section level up to the Project level. Had die author decided to make Element 153 a child of Element 152 instead of a sibling, die next sibling and previous sibling pointers of Element 152 and Element 153 would have been respectively voided, die first child pointer of Element 152 would be set to point to Element 153 and die parent pointer of Element 153 reset to point to Element 152. Adding new Elements would proceed in an analogous fashion. Thus, an Element has (i.e., in its instance data structure) pointers to: (i) its parent Element; (ii) its first child Element; (iii) its previous sibling Element; (iv) its next sibling Element; and (v) its first child Modifier. 90 i 26 (2) Modifier Connections. The Modifier objects shown in Fig. 25, namely 161, 162 and 163 (and Services 168, 169 and 170 in Fig. 26) are not implemented as conventional C + + classes, as is the rest of die core 99 (and thus are represented specially as double rectangles). These Components (Modifier and Services) are special classes of objects designed to extend die functionality of die external architecture discussed above. They will be discussed in more detail below in connection widi die Component API. To bridge die core 99 architecture wid the Component API, a "wrapper" class interfaces with each Component class. There are thus wrappers for Modifiers and wrappers for Services (discussed in greater detail below with respect to the Component API). The Modifier wrappers dius have pointers to: (i) the Modifier; (ii) its parent Element; (iii) its parent Behavior, if any; (iv) its first child Modifier, if any; and (v) its next sibling Modifier. When an author drags and drops a Modifier into an Element, a Modifier object is created. In other words, a Modifier wrapper object is instantiated from a Modifier wrapper class (as is a corresponding special Modifier object, such as Modifiers 161, 162 and 163, discussed in greater detail below with respect to the Component API). These Modifier wrapper objects are instantiated from a general wrapper class, except for Behavior Modifiers, whose wrapper objects are instantiated from a Behavior wrapper class. These wrapper classes provide for die Modifiers a backbone of mediods to read and write data, to obtain and draw the Modifier's icon, to open and close die dialog editor, to copy data, and to send messages throughout ie Su-uctural and Behavioral Hierarchies. Focusing now downwards from Element 153, one can see mat it points to its first child Modifier 161 dirough Modifier wrapper 158, which in turn points to the second child Modifier 162 dirough wrapper 159, which in turn points to the third child Modifier 163 dirough wrapper 160. Element 153 is itself pointed to by die Modifier wrappers 158, 159 and 160. Thus, die Element 153 knows of its first child Modifier 161, and all diree sibling Modifiers 161, 162 and 163 know of dieir parent, Element 153. With the sibling pointers going in only one direction (right), one can see diat die Modifier wrappers 158, 159 and 160 form a singly-linked list. This is distinguished from the sibling Elements 152 and 153 which form a doubly-linked list. This slight difference in the implementation of the Structural and Behavioral Hierarchies is due to a subjective judgment mat, in practice, it is more often necessary to know one's previous sibling Element man one's previous sibling Modifier. As will be discussed below, messages are passed among Modifiers from "left" to "right," i.e, along the sibling chain. If need be, one can always record die pointer to the present Modifier, proceed up through me parent and dien cycle forward from the first sibling, recording each pointer in turn until die present Modifier is encountered again. Allowing audiors to move Modifiers widiin die Behavioral Hierarchy requires analogous updating of pointers as described above widi respect to Su-uctural Hierarchy changes. (3) Player and Asset Connections. When an audior creates a new Element (e.g. , a Graphic Element), an Element object is instantiated from a general Graphic Element class. In addition, corresponding "player" and "asset" objects are instantiated from dieir core classes. From Element 153, one can also see attached a player 154 and asset 155. The player 154 knows how to "play" media of a particular type, e.g. a PICT, a sound, or a QuickTime™ movie. The asset 155 is a pointer to the actual media, which is represented as stored on disk 157. Of course, die operating system 156 provides the necessary interface between the asset 155 and media 157. In die embodiment discussed here, player 154 performs the bulk of me interaction with Element 153, while asset 155 only exchanges ID reference numbers with die Element 153. The process by which an Element is linked to a player is as follows. When the media file 157 is selected by die audior through a standard file dialog box, die asset manager 7 is asked whedier it knows about mat particular asset. If so, that asset 155 is used and connected as shown. Odierwise, a database endy is created in asset manager 7, the asset 155 is established and the file description is passed on to player 154. If die audior decides to switch the type of media entirely, a new player object would be instantiated, widi all the pointer information carried over from player 154. This morphing process is controlled by die morphing 44 module. Similar to the process of originally creating an asset, a new asset would replace asset 155, while asset 155 would remain as an entry in the asset manager 7. The asset manager 7 would simply decrement me user count in its Asset Palette 70 display, even if diat meant that the user count was now zero. (4) Touch-Up Process. When an author initiates Adoptions or Transplantations, the system 100 attaches and detaches Elements or Modifiers, as die case may be, as discussed above. In order to complete either process, and enable the Element or Modifier to operate in its new environment, a few additional measures are required. When an audior moves an Element or Modifier from one environment to anodier, the system 100 broadcasts an Environment Message from the Project level. As will be understood more fully below, Messaging Management 13 dispatches messages along die Structural and Behavioral Hierarchies not only to Elements and Modifiers, but also to all views, palettes, and certain other "system objects, " in order diat they also may respond appropriately. The message specifies the relevant object and type of change. This change can be as subtle as requesting a view window to highlight an icon selected by die audior. When an object is moved to a new environment, a "touch up" process takes place. This process applies not only to Elements and Modifiers, and each of die objects they contain, but also to assets, symbol IDs, mToon ranges, sound ranges, etc. The system 100, through the Symbol Manager 19, asks each entity to identify by name its "external dependencies" from its previous environment, e.g. , Author Messages, Variables, aliases, mToon symbols and sound symbols. If the name is present in die new environment, and die ID number supplied by the Symbol Manager 19 differs, die system replaces the entity's old ID number with me ID number from the new environment. If the name is not present, yet the ID number conflicts with an existing ID number, the entity is assigned a new, non-conflicting ID number. The implementation of Hierarchical Element Positioning (i.e. that a child Element moves with its parent Element), necessitates its own type of "touch up" process. In the current embodiment, position (an Attribute) only applies to Graphic and Text Elements (although one could envisage and readily implement "stereo" sound Elements, where the Element's position would reflect the relative amplitude between die left and right speakers). In any event, when a parent Element moves, the position of each of its child Elements (and dieir child Elements, and so forth) must be modified. The coordinates of the child Element are readjusted in a straightforward manner by the system, which subd * acts the old parent's coordinates (saved when detached) from the Element's coordinates and adds die new parent's coordinates to die Element's coordinates. Fig. 25 illustrates how to access a parent's data structures, and dius in particular, its position Attribute. b. Aliasing. The alias manager 8 works with all Modifiers and operates by maintaining a list of all aliases, along with the users of such aliases. In the current embodiment, all manifestations of an alias are separate instantiations of a Modifier which are kept in sync with each odier. Thus, the relationship of an aliased Modifier to the objects it connects with (pointers to Elements, parent Behaviors, sibling and child Modifiers, etc.) is kept intact. Each instantiated Modifier has an alias ID code which is set to zero if not an alias, and will share die same non-zero alias ID code when aliased togedier with others. Thus, if one of the Modifiers under an alias is changed, the Modifier state data is written out and die alias manager 8 transmits the data to die odier Modifiers under die alias. For Variables, this can and does occur in Runtime Mode. For all other Modifiers, this occurs only in Edit Mode. This accounts for the ability of aliased Variables to circumvent dieir normal scope. Of course, it should be noted diat this is an implementational decision only, and anyone of ordinary skill in die art would realize d at non- Variable Modifiers could easily be synchronized at Runtime as well. 2. Saving Projects and Titles. As was discussed above, die Project's Elements and Modifiers are stored in Logic 1, while the various files may be dispersed in whatever fashion in the storage for media 2 (e.g., directories for files stored on magnetic media, CD-ROM, etc.). It is wordi noting how the title builder 51 actually allocates storage (on a medium such as CD-ROM) for a standalone title, radier dian a Project under development, such mat die object loader 16 can efficiently load objects into memory. With die slow seek and read access time of CD-ROM, it is important to advantageously arrange data diereupon so as to minimize the amount of read -head dirashing. In one embodiment, the logic 1 and various media 2 files are all placed in one file container, which is a contiguous arrangement of all the files, and which only has to be opened by die operating system once, always a costly operation in terms of time. Each asset will be written to disk in its rawest form, as nothing but the application itself will need to access the asset. Thus, a picture will be a compressed bittnap, rather dian a PICT. It is thus imperative that the computer running die title be able to know where everyd ing is within this file container, as it cannot resort to the operating system file utilities. Thus, widi reference to Fig. 27, one can see a cross-section of die available tracks on the CD-ROM 175 (neglecting the track curvature here for clarity). The actual application code 176 precedes all odier data and is loaded into memory first. The Runtime engine embodied in the application code 176 would include all used players, Modifiers, Services, etc. Thereafter, die Structural Elements 177 (i.e. Project, Sections, Subsections), as well as Scenes, are stored and are all loaded in memory for the entirety of the title operation. The actual act of loading instantiates each of the objects in this embodiment. The assets of individual Scenes are stored, each in turn, widi die table of assets for the given Scene as a "hidden" asset. These tables of assets written to disk by die title builder 51 would be stripped of everydiing unnecessary for die title. Thus, unused assets as well as the user count are discarded. The asset manager 7, in conjunction with die title builder 51 , also would have scanned me Scenes and correlated the order in die asset manager 7 database widi layer order number for each of die Elements in the Scene before writing diese assets and the tables of assets to disk. In this example, there are diree Scenes (Scene 1, Scene 2 and Scene 3), each with a table of assets 178, 181 and 183, respectively, which provides indices to all the assets within die given Scene. These are loaded, respectively, immediately preceding the beginning of die playing of dieir corresponding Scene. A flag in me table of assets determines whedier an asset should be preloaded, meaning that die asset will be loaded immediately after the asset table is loaded and inspected, and memory allocated to die asset locked down. Following each of those tables are all of the objects (Elements and Modifiers) 179, 182 and 184, 96 1822 PCIYUS96/0 4 respectively, associated widi each Scene. Thereafter would be stored individual media, as for example shown here for Scene 1, a background picture 180. Typically, to save space, assets are stored in only one place on die CD- ROM 175. However, in order to minimize the read-head movement, and dius enhance Runtime performance, me asset manager 7 may be configured, during die authoring process, to store assets used more man once in multiple separate places. The order in which the media are presented in the asset manager 7 is me order in which the tide builder 51 writes out die title for CD-ROM. It is thus also advantageous if the assets which are to be preloaded be up at die front of die asset manager 7, for the reasons discussed above. 3. Runtime Functionality. Under die classification of Runtime functionality with reference to Fig. 24, one finds a world manager 10, a component manager 20, and die cross-platform architecture 50. The world manager 10 and component manager 20 can be referred to collectively as the core 99 (see Fig. 29). The world manager 10 controls the overall processing of die Runtime functions and includes an asset manager 7, an alias manager 8, hypertext support 9, asset classes 11, media player classes 12, messaging management 13, a rendering manager 14, a sound manager 15, an object loader 16, memory manager 17, thread manager 18 and symbol manager 19, some already discussed above. The asset classes 11 are die basic classes which describe die external resources, as for example fonts, pictures, movies, sounds, etc. The media player classes 12 govern the low-level Runtime operation of a Project or title. They include picture players, movie players, sound players, etc. 97 The messaging management 13, discussed in more detail below, is the subsystem which controls the dispatch and targeting of messages among objects. Rather than operating on a method-to-memod call basis, which often is unwieldy and slow, messages are dispatched dirough a communication network, relying heavily on the Su-uctural and Behavioral Hierarchies, widi these destinations resolved and optimized at Runtime. The rendering manager 14 renders bitmaps to the display 3. The rendering manager 14 may also maintain alternate off-screen buffers, or "GWorlds. " All draw commands are accumulated for optimal concurrent drawing operatior during idle processor cycles, as discussed below. The sound manager 15 controls the audio signal that is transmitted through die speaker 4. The object loader 16 reads in definitions of die various objects (e.g. the instantiated Elements and Modifiers) for the particular title/Project from the logic 1 storage. The memory manager 17 performs the low-level allocation of memory for the system. The iread manager 18, as discussed more fully below, controls the multitasking threads of system 100, whether posted by die system 100 itself, by the Modifiers 22, or by the user interacting dirough the keyboard 5 or mouse 6 or other peripheral. In one embodiment, for the Apple Macintosh™ operating system, all threads are cooperative or real-time, cooperative meaning all odier operations are suspended until a diread declares itself done, and real time meaning that they operate at a fixed time by invoking an interrupt. The former type is implemented with a list of timers, widi regular checks to see if the timer has expired, and if so, processing the corresponding thread as soon as practicable. The latter type under the Macintosh operating system should only be used for short tasks; otherwise the system is likely to fail. The symbol manager 19 associates names of objects with internal reference IDs. Given one, it will return die odier. It is called upon by various modules diroughout die system 100 to produce lists of messages, Elements, Modifiers, etc. The component manager 20 (discussed in greater detail below) implements the extensibility of the architecture in accordance widi the present invention, and includes the component API 21, a plurality of Modifier classes 22, me Service manager 23, and a plurality of Service classes 24. Both die Modifier 22 and Service classes 24 are coupled to the system dirough die Component API 21, which is the application programmer's interface that enables the core 99 of the system 100 to communicate with the various Components (Modifiers and Services) created by programmers. The Component manager 20 permits programmers to add custom Modifiers and Services to the system. The Component API 21 actually permits Modifiers 22 and Services 24 to interface with each other as well as widi core functions. The service manager 23 inventories and manages die various Services 24, controlling, for example, how Modifiers become (or are removed as) clients of particular Services. The Services 24 are, generally speaking, groups of functions or functionality accessible by a Modifier. Some key Services implement such vital functions as determining an object's parent, detecting collisions of Elements or providing time-of-day functionality. The ability to add additional Services represents enormous extensibility of the functionality present in the system. For example, one could write an 99 AppleScript™ Service which would allow scripts to be written through an AppleScript Modifier and give access to the already-developed capabilities of die AppleScript language. Anodier example, discussed in more detail below, is to provide a "gravitational" service, with a gravity Modifier giving "mass" to its Elements. Both Modifiers 22 and Services 24 use a form of dynamic binding, resolved at Runtime, implemented using the object model hereinafter described. This yields enormous flexibility in the overall design. For example, patch code can be provided separately and be incorporated into the system 100 during the Runtime binding process, overriding the existing code. Finally, die cross-platform architecture 50 controls the access to low-level features diat are platform-dependent. For each function diat must be performed on die display 3 or dirough die operating system, a generic method call is made, which in turn makes the platform-dependent method call. This generic call may invoke a real function which prepares whatever overhead is required for the particular platform, or it may be simply a macro which invokes the platform- dependent function directly. The former scenario would occur where structures are not easily reconciled between platforms, as for example a window under die Apple Macintosh™ operating system as compared with one under Microsoft Windows™. Under diese most extreme circumstances, a placeholder class is created to handle both implementations. Thus, under die present invention, a title need not be "ported" to another platform - i.e., the code targeted for one platform need not be rewritten to run for a new platform. For example, die title can be built by title builder 51 in accordance widi die platform-dependent mediods for die various platforms supported by die system (e.g. , Apple Macintosh™ 68K, PowerPC and Microsoft Windows™). In one embodiment, die particulars of dialog screens, for example the Modifier configuration dialogs discussed in depdi earlier, are stored as device- independent scripts within the application, dius providing die dialogs for each platform transparently. This overall design philosophy prevents the various abstract functions from becoming too tightly bound to die implementations of a particular platform, which is the typical headache of die normal porting process. Typically, software quality assurance approaches would be fixated upon concentrating on only one platform implementation at a time, and freezing features until the overall su-ucture is stable. The multi-platform approach here resolves this porting problem. The functionality of the Runtime environment involves two major processes: (i) message targeting and dispatching, and (ii) event loop processing, both of which merit further discussion. a. Message Targeting gnd Dispatching. Typically object-oriented audioring systems provide no special mechanism for dispatching messages among objects. They simply rely on method-to-method function calls which necessitate a laborious search dirough function tables to access the proper methods. By conu-ast, under die principles of the present invention, messaging is accomplished by means more akin to a communication packet-switching system. The problem posed in optimizing performance with regard to messaging is how to account for target destinations which may not yet exist at die time of audioring, yet not incur a time penalty for each message when the system searches tables for die proper target. This problem is exacerbated by die freedom afforded under the present invention to drag and drop objects from one environment to another. The data structure for messaging in one embodiment of die invention is presented in Table III. TABLE m. MESSAGE DATA STRUCTURE Member Type Description f nfo long Flags describing die characteristics of the message, including whedier die message be sent immediately, cascaded or relayed. fjeeysig long Special password for accessing proprietary Modifiers. f_sender void* Identifies die sender of the message. f_event long The ID code corresponding to die message name. f_eventinfo long Adds any additional information for the message. f_targetinfo struct The destination target information. f_data union The various kinds of data (e.g. vector, anodier event) that can be sent widi the message. Referring back to Fig. 1, consider the scenario in which die audior desires diat a Modifier M4 117 on Element E3 110 send a message to Element E2 109. Thus, die first step is to make available all possible destinations for Modifier M2 115 to die audior in Edit Mode, as for example, through the Destination pop-up menu of the Modifier dialog. The Messaging Management 13 accesses the data structure of Modifier M4 117. Under die embodiment here, recalling the discussion above with respect to Fig. 25, one can readily understand how die Messaging Management 13 can access the ID code of its parent, in this case Element E3 110. Knowing Element E3 110 allows Messaging Management 13 to access its data structure, yielding the ID code of parent Scene Scl 106. It is clear that this process can thus be readily bootstrapped, to reproduce die entire Sttuctural and Behavioral Hierarchies. Yet, in this embodiment, Messaging Management 13 only proceeds further to discern the chain of ancestors, from Scene Scl 106 to Subsection SSI 104, Section SI 102 and Project 101. Element E3 110 could also yield its previous sibling, namely Element E2 109. However, in the current embodiment, me siblings of Element E3 108 are obtained in a different manner. Knowing the parent Scene Scl 106, one can obtain the pointer to its first child, namely El 108. Then, Messaging Management 13 proceeds down the sibling list, namely Element El 108, Element E2 109 and ending here widi Element E3 110. Messaging Management 13 does this by broadcasting an identification request message to the Scene Scl 106, which filters down one level so diat die children of Scene Scl 106 identify diemselves as well. The process of locating the siblings of modifier M4 117 employs an analogous identification request broadcast, this time to Element E3 110. The actual translation of ID codes into names for presentation to the author is accomplished by die Symbol Manager 19, which maintains all such name-ID code correspondences. Thus, die Destination pop-up menu is populated widi all the actual names of these Elements and Modifiers, including Element E2 109. Thus, when the author references a target by name, the appropriate ID code is stuffed directly into die fjargetinfo piece of the message data structure. This whole process was referred to above as Direct Targeting. However, the author might not want to reference by name, as for example, in the interests of reusability. Thus, the audior can reference a target by "tag," a stand-in for most of those very same destinations presented in me Destination pop¬ up by name, and as described above as Relative Targeting in conjunction widi Table II. Unlike die bootstrapping process discussed above, diis process resolves the ID codes by proceeding directly up dirough die Structural and Behavioral Hierarchies, accessing die nearest-neighbor sibling Elements directly from die Element's next and previous Element pointers, rather dian by die "identification request broadcast" procedure. Once die proper ID code has been resolved at Runtime in the first instance, the ID code can be stuffed into fjargetinfo, allowing the messaging to proceed in a targeted manner thereafter. The embodiment discussed above permits targeted messaging to initial destinations widiin a somewhat fixed scope. It is suitable in most instances where 103 there is a close relationship among Elements, or the number of Elements is rather small. To communicate to an Element outside this small family of Elements, in this embodiment, requires targeting the most recent common ancestor Element. The message will cascade down to that Element's progeny, including die real target Element. For example, Modifier M2 115 could not target Element E4 111 directly in this embodiment, because die parent of Modifier M2 115 (Element E2 109) is neidier an ancestor, child or sibling of Element E4 111; rather it is only an "uncle" of Element E4 111. Thus, Modifier M2 115 could target the most common ancestor of Element E2 109 and Element E4 111, diat being Scene Scl 106. Thus, Scene Scl 106 would pass die message to its children, Elements El 108, E2 109 and E3 110. It is worth noting that in the embodiment discussed here, Element El 110 would pass the message to Element E4 111 before the message is passed from Element El 108 to Element E2 109 (showing a preference for one's children over one's siblings). In an alternate embodiment, however, it may be desirable to modify die Structural and Behavioral Hierarchies at Runtime, through Dynamic Creation (i.e. , instantiation of objects), Transplantation or Adoption. Under this scenario, the destination might best be resolved each time the message needs to be sent. This would allow Relative Targeting to work, even though we have, in essence, "moving targets. " To permit an audior to achieve diese dynamic functions, one merely need create a set of Modifiers which specify the conditions under which such events can occur. b. Event Loop Processing. The management of all tasks related to die execution of an application requires allocation of processor time among such tasks. Thus, widi reference to Fig. 28, this process starting from block 250 may be described. In one embodiment, utilizing the Apple Macintosh™ operating system, various tasks may operate concurrently under what is known as cooperative multitasking, meaning mat a task must surrender use of the computer's processor in order diat anodier task may be serviced (as opposed to pre-emptive multitasking, where the processor may be usurped by another task without a declared surrender by the first task). Thus, die decision box 251 represents the release of the processor by the operating system (including odier applications and background network functions, for example) to system 100, which then performs pending tasks if the operating system is in what is termed here as an "idle cycle. " If die processor is not idle, and die operating system itself is not running some other task, the World Manager 10 determines whether there are any pending messages to any active Services or Modifiers at step 252. If there are any active Services or Modifiers, diese Services and/or Modifiers are queried to determine whedier processing such a message may be deferred at step 253. This is a decision diat may be based on a lack of urgency, or whedier die processing prompted by such message would hamper performance were it done at a time- critical moment, or various other factors. Thus, processing that needs to be done immediately is done at step 254 while deferred processing is scheduled dirough die posting of a thread at step 256 by die diread manager 18. One may even envisage a hybrid situation where some small amount of critical processing is done immediately while the rest is deferred dirough a posted diread. The final step 255 of die "non-idle" state is to relinquish the processor to the operating system to perform all its other tasks. The idle cycle commences by a trigger for the animation of the Shared Scene 257. This step does not perform the actual drawing; rather, it is an opportunity to post draw commands for later implementation. This streamlines the actual drawing process, e.g., eliminating the need to draw portions of the display 3 due to motion in one layer when a covering layer mat obscures die Element in die first layer continues to cover mat portion of the display 3. It should be noted here that, whenever an Element is moved, prompting a draw command to show such movement, each of die Element's children is notified that die parent was redrawn, so each child Element can then post its own redraw command. Thus, children Elements can follow their parent Elements in accordance widi die Hierarchical Relative Positioning mechanism discussed above. Next, animation of the currently active Scene is triggered at step 258 and similarly handled. Next, all previously posted threads (eidier posted by Modifiers or Services at step 256, or by the system 100 itself) are processed at step 259. Thus, all motion Modifiers would proceed to move their Elements according to dieir prescribed manner of motion. Messenger Modifiers, if triggered, would post new messages to die system 100. Services would perform their "idle" processing, and so on. Thereafter, all accumulated draw requests are performed at step 260. Each redraw command is specified by invalidating the old and new visible regions of the corresponding Element. As described above, mat may be driven by posted requests from the Elements, or by Motion Modifiers, etc. There may be instances where particular Elements need to be notified diat such drawing operations occurred. This decision is represented by step 261. For example, a QuickTime™ movie needs to know when to start its sound. Thus, such Elements would be so notified at step 262. A similar housekeeping function is step 263, which inquires whedier any sound files diat were previously playing have actually ended. If so, dien any necessary "end play" procedures can be executed (e.g., deallocating the memory taken up by the sound file). In odier words, die corresponding Element receives this Environment Message and transitions to its "end play" state. Finally, step 265 decides whedier the idle process should relinquish conttol of the processor. There are tides, such as games, that have a significant amount of user interaction and screen updating diat necessitate the use of a large fraction of die total processor time. On the odier hand, a networked computer needs to perform regular background tasks to keep the network connection up and running. Thus, a sliding scale is established by die title's author, or set by a user, between die extremes of never giving up control (squeezing out all odier tasks) and always giving up conα-ol (and suffering a performance penalty). The outcome of mis decision step 265 is determined in accordance widi this sliding scale. When no system time is made available, die World Manager 10 must do the checking for the mouse 6 and keyboard 5 events. When a mouse down event occurs, die World Manager 10 will continue to track the mouse 6 while it is being dragged, although it will intermittently give up time to odier threads, including die idle process. It is up to the World Manager 10, which knows the positions of all Elements, to determine which Element was selected in this manner. C. Component API — "Programmer Eye View". The current embodiment of the invention is geared toward almost unlimited extensibility. Programmers can add Components (Modifiers and Services that support diem) that extend die system's architecture. These Components are indistinguishable from me system's built-in Modifiers and Services, which implement much of me system's external architecture discussed above. Thus, from the audior's perspective, die system is extended seamlessly by the addition of new Modifiers (and supporting Services) to which the audior has full access. Widi reference to Fig. 29, one sees a plurality of modifiers 22a, 22b, 22c, ..., 22z and a plurality of services 24a, 24b, 24c, ..., 24z coupled to die core 99 of system 100 through die component API 21 as plug-in Components. The core 99 in this embodiment is implemented through ordinary C+ + classes. However, die modifiers 22 and Services 24 are not ordinary C+ + classes. To permit extensibility of the system, they are implemented through die "MOM" object model described below. In order to handle diese "new" Modifier /Service classes, "wrapper" classes 94 and 95 of die ordinary C++ type are provided to interface widi diem as was discussed above in the context of Figs. 25 and 26. Through diese wrapper classes, die Service manager 23 controls the Services 24 and d e world manager 10 and Component manager 20 instantiates Modifiers, such as Modifier 96 illusu-ated in Fig. 29. The world manager 10 also instantiates Elements, such as Element 97, which are coupled to corresponding instances of a media player class 12 and an asset class 11. It will be well understood to diose of ordinary skill in die art diat the media player classes could diemselves be migrated out of the core 99, operating under the object model of the present invention and connected dirough a wrapper class and an API analogous to die Component API 21, making me types of media die system 100 can interact with an extensible feature as well. Object Model. The object model underlying diis invention can be described as "shock proof. " It lies along a spectrum in between "rugged" and "fragile" object models. A rugged object model would permit a programmer to change dynamically virtually any aspect of die class hierarchy (e.g., adding, modifying or deleting parent classes, subclasses or intermediate classes) without requiring recompilation or other modifications of existing classes. A fragile object model, on die odier hand, would not permit a programmer to make any such changes dynamically. The mFactory Object Model ("MOM") of diis embodiment represents a compromise between these two extremes. Rather than incurring the overhead and performance penalties of a rugged object model, MOM permits a programmer dynamically to add subclasses, or add methods and/or fields to or odierwise augment superclasses, provided diat me order in me class hierarchy is preserved. In diis manner, most of die functionality that a user/audior would desire as extensions to die system can be provided widi minimal overhead, as compared to a rugged object model. One aspect of MOM is diat, at compilation time, each class identifies its associated superclasses and dieir estimated sizes. At Runtime, the class hierarchy is verified, particularly whether die sequence of classes is preserved. If it is preserved, dien MOM adjusts for any differences in die sizes of die class structures by changing the offset field for each class structure to reflect the new difference in size. This permits new fields to be added to each class structure or enu-ies to be added to die virtual function table (vtable) dynamically without global recompilation. If the class sequence is not preserved, die system will not crash; rather, die affected object(s) simply will not run. Anodier aspect of MOM is its use of virtual tables. Programmers can access die virtual tables of their classes as well as the virtual tables of the superclasses above. The tables are created by die system and resolved upon loading. One can add fields and methods, diough one cannot later rearrange diem wimout a full recompile. One key advantage of diis construct is that adding fields and methods to a superclass does not require recompilation of its subclass below. With reference now to Fig. 30, die operation of MOM is described in detail. In Fig. 30, one sees a class hierarchy of classes "A", "B" and "C" represented by "self" class structures 126a for base class "A", 126b for class "B" , and 126c for class "C". Prepended to each of die class structures is a pointer to the class' entry in vtabs 127, a table with pointers to each of die virtual tables present in the A/B/C class strucπ re. In one embodiment, die pointer preceding die "self" structure is not directly accessed by the programmer, but rather is provided indirectly dirough a function call, relieving d e programmer from the implementational details diereof. From the pointer to the class structure 126c for class "C" , for example, the pointer to its corresponding enu-y in vtabs 127 is obtained. From the appropriate pointer in vtabs 127 one can then recover die pointer into die appropriate vtable 128c for class "C". With such a pointer, one can then obtain the actual function pointer in the methods storage 129 to die appropriate method 129a, 129b, 129c, etc. In one embodiment, die vtable contains not only the function pointer, but the slot number of the class containing the version of the method diat class "C will call. Thus, if vtable 128c had for a particular function a slot number of "2", it would mean "Cs" function would be called; if it had a slot number of " 1 ", "B's" function would be called, and dius a slot number of "0" would designate the use of "A's" function, i.e. no overriding. It is dius clear how the system is polymorphic, in that you can both override (replace die existing functionality) and overload (add to die existing functionality) methods of a subclass. As our example of overloading, for die "CompConstructor" method 129b shown here (which represents the method diat creates or "constructs" a Component instantiation for class "C"), one could perform all the construction necessitated by class "C" itself, but rely on the construction performed by class "B" dirough an "Inherit" function which invokes "B's" class dirough its slot number. In the embodiment discussed here, die programmer's selection of either overloading or overriding is invoked dirough a function call, sparing die programmer from the implementational details of diis bootstrapping. In actuality, die base class methods are accessed through C- function calls which reference the base class method dirough the corresponding slot number in the vtable. With the above mechanism in place, it is clear how the "shock proof" mechanism of MOM works. If a programmer wished to add a new mediod 129z, say, to class "B", such method would be appended to the end of the existing methods 129a, 129b, 129c, etc. (though diis time for class "B"). A new entry pointing to diis method would be made in vtable 128b, at the end of diat list. This would necessitate expanding die size of vtable 128b, and d us subsequent vtables (in this case vtable 128c) would be pushed back accordingly. The corresponding endies in vtabs 127 for the vtables subsequent to class "B" would dius also be updated to reflect this offset change. Changes in any of the class self data structures 126 diemselves will be discussed in die context of Modifiers below. A further advantage of diis implementation is that a programmer can write Components as "C" functions, and MOM will treat these functions as methods of an inherited subclass. All die apparatus, as mentioned above, for maintaining this class hierarchy is hidden to such programmers dirough function calls. 2. Component Methods. On an object-oriented level, Components comprise a MOM class hierarchy. The base Component class, "_Component", provides for three mandatory methods: (i) a creation/instantiation routine; (ii) a duplication routine; and (iii) a deletion routine. The mandatory mediods are diose which die core provides no default for, or for which the class would have no independent meaning absent its own method. In accordance wiώ die object authoring interface discussed above, diese would be invoked, for example, when: a Modifier is dragged from the Modifier palettes 35a or 35b; an existing Modifier is selected and die "Duplicate" menu item is selected or die "Command-D" key sequence is typed; or, when an existing Modifier is selected and die "Delete" key is typed. The various Components are either direct subclasses of _Component, or themselves may form a hierarchy, such as me Messenger Modifier having as a subclass die If Messenger. 111 In addition to die mandatory methods listed above, a typical Modifier would include at least two more methods: (i) presenting die audior with the Modifier's configuration settings; and (ii) committing the author's modifications of diose settings to memory. These would be invoked, respectively, when die audior double-clicked on die Modifier's icon to bring up die Modifier's dialog box, and when die author clicked die "OK" button in lieu of the "Cancel" button to save all audior changes. A representative sample of the virtual functions of _Component in the current embodiment are described in Table IV as follows. TABLE IV. BASE COMPONENT CLASS FUNCTIONS Name Description Comments Complnit entry point to Component Mandatory methods methods (main function in C program). CompConstructor Create Component. CompCopyConsd-uctor Duplicate Component. CompDestructor Desu-oy Component. CompEditorOpen Prepare for Modifier edit. Editor mediods CompEditor Accept Commit edits to Modifier. CompProcessMessage Act on message received. Message processing methods CompEventCount Query Component as to the number of events it responds to. CompGetEvent Query Component as to a particular event it responds to. CompSetEvent Set Component to respond to a particular event. CompGetService Get pointer to Service. Service methods Name Description Comments CompAddClient Register Component to Service. CoηipDeleteCl ient Unregister Component from Service. CompGetProperty Get stored Variable. Variable methods CompGetPropertyCount Get number of stored Variables. CompSetProperty Store Variable. CompGetSavelnfo Asks a Component what Save/Restore revision it is, and its size. methods CompRestoreComponent Restores the state of the Component as previously saved. CompSaveComponent Saves die state of the Component upon exiting application. CompAddThread Adds a new diread for Thread methods execution. CompKillThread Deletes a given diread from further execution. CompCalcuIateDrawParams Particular drawing Miscellaneous CompDrawDeviceContext functionalities, especially methods CompDrawMedia to alternate screen CompGetClipRegion "GWorld". CompGetMargins CompPostDrawMedia CompDrawGWorld CompPostDrawGWorld CompPreDrawWorld Name Description Comments CompEditorAcceptChanges Particular editor CompEditorDeclineChanges functionalities. CompEditorldle CompEditorltemAdjustCursor CompEd torltemChanged CompEditorCustomDraw CompEditorCustomClick CompEditorltemTyping CompEditorltemTyping CompEditorValidateChanges CompOpenMediaStream Access to particular location in file of stream created by anodier When a Component is first registered (as discussed below), a structure is created containing any class-wide data (in C language syntax): typedef struct { struct** f_vtabs; long* f_soffsets; short f_cindx; } MFCDRec; where "f_vtabs" represents the pointer to the vtabs table, i.e. the table which points to all virtual tables, from which the class' virtual table may be derived; "f_soffsets" is a table of offsets from the root of each self record in each of die base classes; and "f_cindx" is die Component index, which is an index maintained by die Component Manager 20 which allows the Component to access common information about such Component, such as its name. This structure is appended widi die instance data. An offset is used to allow for any changes in the size of structures of classes above it. Thus, the offsets are calculated at registration time (described below), allowing pointers to be calculated up the class hierarchy dirough die f_soffsets table. It should be noted that f_vtabs is assigned at the end of registration, when the objects have been loaded and all offsets in vtable sizes have been adjusted accordingly. In actuality, die embodiment of MFCDRec in the Apple Macintosh™ 68K implementation contains one more structure member, "f_A4", which is a long integer. One drawback of die 68K system is the inability of code resources to have their own globals, such as strings or initialized variables. A normal application can have such globals, with register A5 pointing to me top of such global data. Thus, particular globals would be accessed via offsets with respect to A5. Register A4 is used as the pointer to a code resource. Thus, if one code resource calls anodier 's code resource, one could not know where that code resource's globals were, as ώere was no way of knowing what that code resource's A4 value was. Thus, dynamic loading on die 68K could not include globals, unless one was prepared to save and restore A4 pointers each time one code resource called anodier. In die present embodiment, die Component can store the A4 value as well as die slot number of the vtable methods. Thus, diere is no need to bracket method calls from one Component to anodier which set up and restore die values for A4. Thus, a transparent mechanism is provided to access globals within each Component. An example of an instance data structure is presented in the case of a "gravity" Modifier, which would add "mass" to Elements, prompting them to "fall" in the presence of the gravitational "force," implemented as discussed below, dirough a Service. Thus, the structure for the instance data could be as described in Table V: TABLE V. SAMPLE INSTANCE DATA STRUCTURE Member Submember Type Description f_enableEvent fjype short Specifies die enabling event. f_event long f_event_info long f disableEvent fjype short Specifies the disabling event. f_event long f_event info long f mass fjype short Specifies the Element's "mass". f_value double fjastvector fjype short Specifies the Element's "position". f_angle double f_magnitude double f_pixelvelocity fjype short Specifies the Element's "velocity" in pixels. f_value.PNTX short f_value.PNTY short f_totalMoved PNTX short Specifies the total displacement since the Element started falling. PNTY short f_startTime — long Specifies die time the Element started falling. For the class-wide data one could have simply (in C language syntax): typedef struct { double g_constant; } MFClassRec, *MFClassPtr; where g_constant is the gravitational "constant, " expressing die overall strength of the gravitational force. By making it class-wide data, one could dien easily override diis data (e.g., widi die electrical "constant," turning die gravity Modifier into an "electrical force" Modifier, die mass being replaced by electrical charge), yet leaving undisturbed all other mechanisms of die gravitational Modifier. 116 3. Registration Process. Having explained what Components are and how diey are created, the process of seamlessly integrating diem into the system is now described. In one embodiment of die invention, Components are loaded into die system at boot-up time. They are stored in "kits", special files containing code resources. In die Apple Macintosh™ 68K operating system, these code resources would be designated of type "XOBJ," each code resource accessible dirough its identification number and name. In die Macintosh PowerPC™ system, diey would be stored as code fragments. Under Microsoft Windows™, these kits would be dynamic-link libraries (DLL's) widi a particular file extension, e.g. ".MOM. " The process by which each Component becomes known to the core 99 is called registration. Each Component is identified through a unique 16 character ID string. In one embodiment, diis ID string is the numeric representation of the exact time the Component was first created. The revision number of a particular Component is controlling in the event the application encounters die same Component (as evidenced by its ID string) among multiple kits. This is a very useful feature in die event patch code, bug fixes or enhancements for such Component are provided. If die core 99 encounters Components with identical ID sd-ing and revision numbers, then the system will retain the first one registered. The actual registration or Component loading process is now described, widi reference to Fig. 31. The process, which starts at step 275, first scans a directory or directories for kit files in step 276. In one embodiment, this would be a special directory named "Resources" at me same level in the directory sϋ-ucture as die application. Next, all kit files are identified at step 277. The file types for die various platforms provide the identifying mechanism as discussed earlier. The total number of Components is determined in step 278. Then, allocating the tables for accomodating all the Components counted is done at step 279. Steps 280-283 represent a subprocess which loops, in three passes, through each of d e kits identified at step 277 above. In step 280, die system initializes die self records for each Component from the given kit, based on die Component's stored values for die sizes dierefor and its class structure order. In step 281, the system initializes each of the methods for each Component as necessary, i.e. filling in die methods diat are being overridden by such Component. In step 282, the virtual tables and vtabs table are created, widi slot numbers inserted into die virtual tables, and actual sizes of self records established by walking up die chain of die real self records in the class hierarchy. The decision at step 283 determines whedier die process should loop back to process further kits. Otherwise, the process terminates at step 284. It can thus be understood, as an additional advantage, how this object model compensates for platform migration in mat readjustments are made in the structure offsets that owe to die difference in byte alignments in data structure packing on one platform as compared widi anodier. 4. Core and Service Utilities. Services can be thought of as providing two basic types of functions: (i) as a repository of common functionality mat can be accessed by different Modifiers; and (ii) as a server, by which various subscribed client Components are serviced. However, Modifiers as well as Services could be configured as servers, clients or both. An example of the former would be a Service performing common housekeeping functions, or a library of mamematical or string functions. An example of the latter would be a collision Service that needs to know where all 118 Elements are positioned in order to decide whedier any two Elements have collided. The collision Messenger is die client of me collision Service for an Element that desires to be informed of collisions. The Graphic Modifier, for example, requires no Service to provide color to its parent Element. However, if one wanted to ensure diat the colors of all on¬ screen objects do not "clash", one might write a "fashion" Service that monitored all such colors and informed an "enhanced" Graphic Modifier of a clash. One advantage of delegating a lot of functionality to a Service is diat it keeps die Modifier's size down, certainly a concern when Modifiers will be multiply instantiated. Anodier advantage of being a Service is diat it may be referenced in Modifier methods by name when set up to be a server, rather dian applying slot numbers through vtables to be accessed. As was seen above, Modifiers and Services interact in a very simple manner. Modifiers may be "users" of a particular Service. Therefore, they must notify e Service when to add or delete them from the list of active users thereof. For example, to write a gravitational Service, one must take into account how all objects with "mass" interact with one another, and so such a Service must know which Elements are "massive", i.e. contain a gravitational Modifier. Thus, die gravitational Service, knowing all the masses and positions, can apply the law of gravitation to change the positions of each massive Element according to die time slice involved. The List class, which maintains a dynamic list of clients, would reflect the active "users" or clients of die gravitational service. As discussed above, die class strucn res and registration processes are entirely analogous for Services as they were for Modifiers. In fact, the only distinction between Services and Modifiers, from a data structure viewpoint, is that a Modifier has a flag set which indicates that it should be added to a Modifier Palette 35a or 35b, while a Service has this flag clear. While Modifiers may be multiply instantiated as the need arises, it would be atypical diat a Service be instantiated more man once. A notable exception would be to instantiate a "GWorld, " an offscreen graphics world, as often as needed, especially for applications that are very graphics-intensive. Referring once more to Fig. 26, one can see that die instantiated Services 168, 169 and 170 (again represented by double rectangles to signify their special class nature) are accessed dirough service wrappers 165, 166 and 167, respectively. The Services are thus referenced dirough a list 164, preferably maintained by the Service manager 23. Because Services are not part of the Behavioral Hierarchy and are not visible to authors (as are Modifiers), diey need not maintain the same pointers linking them together. In essence, diey are independent objects called upon by Modifiers for support. The MOM architecture above permits many modules inside die core 99 to be migrated easily into Components. For example, there is nodiing to preclude die media player classes 12, die draw engine for the rendering manager 14, the memory manager 17, the file I/O for die object loader 16 or die database management system for the asset manager 7 from being implemented as a Service radier dian being in die core 99. Thus, if one needed to scale up die system to handle an enormous number of objects, one could replace die database system of the asset manager 7 with a heavy-duty relational database system. D. Examples. Now that die functionality of an embodiment of the present invention has been explained, die d-ue power of diis invention, widi respect to its ease of design and reusability, can be illustt * ated through particular working examples. Snake. This example serves to demonstrate how "Hierarchical Relative Positioning" and Relative Targeting of messages can be used to great advantage in producing a chained object whose overall motion is complicated, yet is achieved by simple motion and coordination between adjacent links in die chain. In diis example, illustrated in Fig. 32, an implementation of a snake is explained. In die layout view window 320, one notes five ovals representing die segments of the snake (SnakeHead 450, SnakeMiddle (1) 460, SnakeMiddle (2) 470, SnakeMiddle (3) 470 and SnakeTail 490). One may note that each segment has a Graphic Modifier, respectively 451, 461, 471, 481 and 491, that can be configured widi a distinct color for eye-pleasing effect. With respect to die Structural Hierarchy, SnakeHead 450 is die parent of SnakeMiddle (1) 460, which in turn is die parent of SnakeMiddle (2) 470, which in turn is die parent of SnakeMiddle (3) 470, which itself is the parent of SnakeTail 490. Thus, in accordance widi Hierarchical Relative Positioning, movement by SnakeHead 450 is "added" to diat of SnakeMiddle (1) 460, both of which "add" to the motion of SnakeMiddle (2) 470, and so on, until SnakeTail 490 is at the mercy of the motion of all its ancestors. Each of SnakeMiddle (1) 460, SnakeMiddle (2) 470, SnakeMiddle (3) 470 and SnakeTail 490 is equipped widi an identically configured Full Motion Modifier, respectively parts 462, 472, 482 and 492. Each has a padi diat consists of a sixteen step arc which starts from the horizontal baseline (where the segment is lined up wid its parent), takes four increments to rotate 45° about its parent, eight more to bring it to -45° of its parent, and dien four more increments back to the baseline. These motions are out of phase in order to avoid die cumulative curling that could rotate the snake into a circle! Thus, timer messengers are placed on each of diese segments, respectively 463, 473, 483 and 494. Each is set to delay for one-half second and dien transmit a "PreviousLinkStarted" message to its parent, with die cascade option turned off. Widi each of diese segments triggered to start its Full Motion Modifier upon receipt of diis same message, it is clear how a half-second time lag in the motion builds up in die snake. Notice diat by turning off die cascade option, die middle segments are not confused by the message they sent and die message they received, even diough named identically for reusability. It is clear diat one could use different names for each segment's communication with die following one. Yet, one of d e sd-engths of this design, its reusability, shows that one could add an indefinite number of "SnakeMiddle" segments and die snake would still work. It is important to provide a mechanism to start the wriggling process. Thus, a Messenger 492 sitting on die SnakeTail 490 acts as a detector, waiting for a MouseDown event on that segment (as if one stepped on the snake). This Messenger 492 is programmed to send die PreviousLinkStarted message to SnakeTail 490 itself, thus "faking" the propagation of this message from a non¬ existent segment behind. On die SnakeHead 450, die PreviousLinkStarted message is interpreted differently. Rather than triggering an arcing motion, it triggers the SnakeHeadMotion 453 vector motion Modifier, which causes the entire snake to propagate in the direction of SnakeHeadVector 452. Thus, once the whole snake starts wriggling, it can start actually moving ahead. A Boundary Detection Messenger 455 detects whedier die snake hits a wall, triggering a WallHit message which disables SnakeHeadMotion 453 and causes SnakeHit Sound 454 to echo the event. It is clear that diis design is very much an abstraction of a snake. Certainly, one could replace die ovals and arc motion with separate mToon sequences showing each snake segment swaying back and forth, each out of phase but joining smoothly with the adjacent segment so that it looks like one continuous snake. This would certainly build very easily on the architecture provided. 2. Fish. This example serves to illustrate how an object may encapsulate differing Behaviors which are in competition widi one anodier, yet coordinate widi similar objects to produce a global or "collective" Behavior. In this example, illustrated in Fig. 33, an implementation of a school of fish is explained. In die layout view window 320, one notes diree fish 360, 400 and 440 in Scene-A 350. The Graphic Modifier 356 is present simply to give the aquarium a pleasant sea color. Before proceeding further into die implementation, it is useful to consider die physical model upon which diis example is based. Fish have a tendency to school. Thus, there must be a certain probability that a fish, seeing anodier fish proceed in one direction, will follow that odier fish. On die odier hand, fish may spontaneously change direction. This may be due to die perception of a direat, food, anodier fish approaching too close, sheer caprice, etc. Thus, diese two tendencies, to school or to change direction, are in tension widi one anodier. Furthermore, if a fish is constrained to an aquarium, it must at some point reverse direction, otherwise it will crash into a wall. For simplicity's sake, the speed, though not direction, of each fish is constant. Each of these fish 360, 400 and 440 is an mToon Element with an identical Behavioral Hierarchy, hence personality. Thus, the representation of the Behavioral Hierarchy from Modifier 361 dirough 398, contained in fish 360 and seen in die su-ucture view window 330 is die same for fishes 440 and 440. Each fish has four Behaviors: StaylnTank 370, Trend-Setting Behavior 380, Schooling Behavior 390 and Change Vector 395. Most of these Behaviors, as will be seen, are driven by the Tick Messenger 366, which is like die "heart beat" of the fish, sending out a "Tick" message once per second. There are two vector Variables (MyVelocity 362 and NewVelocity 363) which respectively define die fish's present and future headings. The actual motion is performed by die Vector Motion Modifier 365, which is keyed to MyVelocity 362. The Drag Motion Modifier 364 is simply there to allow die user to drag die fish around at will during Runtime. Finally, me Transparent Graphic Modifier 361 is diere to give the background of die mToon the aquarium color. There are some significant Variables placed at the Scene level which govern overall fish behavior: SchoolingProbability 351, SwitchProbability 352 and MaxS witch Angle 355. These could probably be incorporated into die fish so diat one could have different types of fish widi slightly different swimming characteristics. SchoolingProbability 351 is the probability a fish will follow anodier, given its heading. SwitchProbability 352 is die probability that a fish will strike out on its own new heading. MaxS witch Angle 355 defines a maximum change in angle if a fish does sα-ike out on its own. Thus, if MaxSwitchAngle 355 was equal to forty-five degrees, dien die new heading of die fish would be within ±45° of its original heading. Two less significant Variables, TopBottom 353 and LeftRight 354, are simply used as mnemonics for whedier a fish has reached me vertical or horizontal constraints of the tank, respectively. The StaylnTank 370 Behavior consti"ains the fish to stay in the tank. Thus, TB Border Detection Messenger 371 and LR Border Detection Messenger 372 respectively detect whedier die fish has reached die vertical and horizontal borders of Scene-A 350. When eidier happens, die respective Messenger would send a HitBorder message to the fish, widi data equal to d e values of TopBottom 353 or LeftRight 354, respectively. The BounceOffBorder 373 Miniscript Modifier, based on a HitBorder message, executes me following script: if incoming = TopBottom then set NewVelocity.angle to (360-MyVelocity.angle) else if incoming = LeftRight then set NewVelocity.angle to (180-My Velocity. angle) 124 1822 end if send "Change Vector" to Element Thus, me new heading is a reflection off the aquarium wall of the present heading, and such new heading is communicated to die fish. A BounceSound 374 sound Modifier, triggered also by die HitBorder message, is added for extra effect. The Trend-Setting Behavior 380 implements how a fish strikes out on its own. The if Messenger DecideToRandomlySwitch 381, triggered every time the Tick message is received from Tick Messenger 366, sends a message SwitchDirection to the Element when the SwitchProbability 352 exceeds a random number from 1 to 100. The miniscript Modifier InvokeRandomDirection 382, triggered by the SwitchDirection message, executes this script: set NewVelocity.angle to (MyVelocity.angle + rnd(2*MaxSwitchAngle) - MaxS witch Angle) send "Change Vector" to Element Thus, the new heading varies from the present heading by as much as MaxSwitchAngle 355, and such new heading is communicated to die fish. The Schooling Behavior 390 implements the tendency to conform. It is premised on the fact that each fish would notice die heading of odier fish in the school. To simulate iis, each fish broadcasts to Scene-A 350 a "MyHeading" message widi the actual vector MyVelocity 363 as data. It is triggered upon die receipt of die Tick message, plus an additional time delay, via die DelayedMyHeadingBroadcast timer Messenger 392. This delay simulates a "reaction time" for the other fish. By virtue of die broadcast to Scene-A 350, each fish will get diis MyHeading message. This diggers the Schooling Decision 391 miniscript: if rnd(99) < SchoolingProbability then set NewVelocity.angle to incoming. angle end if send "Change Vector" to Element Thus, the new heading will be equal to die heading of the odier fish diat sent the MyHeading message, with such new heading communicated to die fish. The ChangeVector 395 behavior actually implements a change in heading, based on the ChangeVector message issued by any of StaylnTank 370, Trend- Setting Behavior 380 or Schooling Behavior 390. It executes d e following miniscript Modifier 398 script: if NewVelocity.angle < 0 then set NewVelocity.angle to (360 + NewVelocity.angle) end if if ((NewVelocity.angle > 90) and (NewVelocity.angle < 270)) dien set Element, range to LeftCelRange else set Element, range to RightCelRange end if set MyVelocity. angle to NewVelocity.angle NewVelocity 363 is first corrected to be widiin 0 to 360 degrees. Then, die script determines whether die new heading is directed to the left, in which case a left- swimming range of animation eels of die mToon specified by LeftCelRange 396 is used; otherwise, die right-swimming range, RightCelRange 397 is used. Finally, die NewVelocity 363 is committed to die fish's actual velocity, MyVelocity 362. It is clear diat this fish could be improved by allowing for a more continuous range of animation eels based more closely on the fish's heading, and diis can certainly be done in a straightforward fashion. One could also have schools form into "superschools, " where each fish has a fictitious parent, its school, which itself has a heading, say die average heading of all fish in the school. The school would dien broadcast to odier schools. Thus, each school might influence the odier schools to follow diem, though with less probability dian one fish widiin a school influences a sibling school member. This would allow a lot of die mechanisms built into die fish to be recycled at die school level. If one were dissatisfied widi diis fiction of die school parent, one could simply build a more complex schooling behavior into the fish, such as being influenced less by die headings of more distant fish than closer ones. The possibilities are certainly endless. 3. Windowing System. This final example illustrates how die present invention provides selective reusability of object containers in new environments. As was discussed earlier, die difficulty of "mixing and matching" objects across different environments is a fundamental limitation of conventional OOP systems. This example presents two similar, yet distinct, implementations of simple windowing systems created widi an embodiment of die present invention. Each system develops complex functionality in a modular manner. The example then illusd-ates how easily individual modules of one system can be reused in the environment of the odier system, with little or no effort (much less programming) on the part of die audior. The example intentionally mimics the public data structures and methods likely to be present in a traditional OOP implementation of a similar system (such as die windowing system described earlier widi respect to die background of diis invention). In this manner, the distinctions between die interdependencies of classes in an OOP class hierarchy and diis system's isolation of an object container's dependencies on its external environment, should become quite evident. With reference to Figs. 34(a)-34(g), this example will now be discussed in detail. A bevelled window 2100 with tide bar 2120, labelled "Window X," is shown in Fig. 34(a). It can be analogized to die public interface to the base class of the window class hierarchy described above. Analogizing to a derived class, a 1 minimize box 2240 is added to die bevelled window 2200, widi title bar 2220, as illustrated in Fig. 34(b). Clicking on die minimize box 2240 reduces the window 2200, togedier with die title bar 2220, to a small icon (not shown). Finally, dragging capability is added, again analogous to a derived class from a minimize class which in turn was derived from the bevelled window class. In diis regard, bevelled window 2300 can be dragged on display 3 by clicking and dragging a mouse 6 on title bar 2320. The alternative windowing system, illustrated in Fig. 34(d), includes a simple window 2400 (no bevel) with title bar 2420, labelled "Window X'" to denote its pedigree separate from "Window X". In lieu of die minimize capability of the first windowing system, a "window shade" capability is added to window 2500 with title bar 2520. Double clicking diis title bar 2520 causes die window 2500 to be hidden, reducing die display 3 area taken up by the window by an alternative means to icon minimization. In Fig. 34(f), the bevelled window 2600, widi title bar 2620, operates with functionality from both systems. The window 2600 may be dragged around freely via title bar 2620 as in die initial system, but the minimize capability has been replaced widi die "window shade" feature from the second system. Finally, Fig. 34(g) shows die full hybridization of die two systems. The minimize capability is added back in, in addition to die "window shade" feature. Bevelled window 2700 may be dragged around by its title bar 2720, minimized to an icon by clicking on minimize box 2740, and may be "drawn up" in shade fashion dirough a double click on title bar 2720. All features continue to operate in their new environment, with very little integration required beyond simple interface issues. The isolation of dependencies at each step of die process are of particular interest. The implementation of these windowing systems is described below in detail widi reference to Figs. 35(a)-35(g). Apart from the purely structural Elements of Project "WINDOW Example" 2000 (namely Window Section 2010, Window Subsection 2020, Window Shared Scene 2030 and Window Scene 2040), Window X 2100 (illustrated in Fig. 35(a)) contains various Modifiers analogous to die "public interface" of an OOP class. For example, the name of Window X 2100 is stored in string Variable Modifier Name 2101. The coordinates of its bounding rectangle are stored in Point Variable Modifiers BoundingRectJTopLeft 2102 and BoundingRect 2103, while Graphic Modifier 2104 provides its color, and Image Effect Modifier 2105 its bevelled appearance. Miniscript Modifier "CREATE Window" provides a function akin to a creation or initialization method which often is executed at die beginning of the Scene 2040: set position.x to BoundingRectJTopLeft. x set position.y to BoundingRect_TopLeft.y set height to BoundingRect_BottomRight.y - BoundingRect TopLeft.y set widdi to BoundingRect JBottomRight.x - BoundingRectJTopLeft. x The position of Window X 2100 is set to the bounding rectangle's upper left-hand corner, and it's dimensions are set by the bounding rectangle's height and widdi. The title bar "TitleBar" 2120 is a child of Window X 2100, and it too has a "public interface" comprised of point Variable Modifiers TitleRectJTopLeft 2123 and TitleRect_BottomRight 2124, which form the bounding rectangle of title bar 2120, with Text Style Modifier 2121 which sets the title's font size and style, a Graphic Modifier 2122 which sets its foreground and background colors (black and white, respectively). The Miniscript Modifier "CREATE TitleBar" 2125 is the creation "mediod" for TitleBar 2120 and is executed at the beginning of Scene 2040. set text to Name set TitleRectJTopLeft.x to 0 set TitleRectJTopLeft.y to 0 set TitleRect_BottomRight.x to BoundingRect BottomRight.x - BoundingRectJTopLeft.x set TitleRect_BottomRight.y to 20 set position.x to (TideRectJTopLeft.x+TitleRect_BottomRight.x-width)/2 set position. y to (TitleRect_TopLeft.y+TitleRect_BottomRight.y-height)/2 The text of TitleBar 2120 is set to Name 2101. The bounding rectangle of the title "area" is set to the top 20 pixels of Window X 2100, and the position of die TitleBar 2120 is centered within such bounding rectangle. Thus, the non-functional appearance of window 2120 in Fig. 34(a) is obtained. Minimize box "MinBox" 2240, illusu"ated in Fig. 35(b), is then added to window "Window X + MinMax" 2200 with TitleBar 2200. The functions of all Modifiers 2201-2206 and 2221-2225 are identical to die corresponding Modifiers 2101-2106 and 2121-2125, and dius need not be repeated here. However, both window "Window X + MinMax" 2200 and TitleBar 2226 have identical (in diis example, aliased) versions, respectively 2207 and 2226, of Behavior Modifier MinMaxResponse. Its purpose will be understood in conjunction widi a description of MinBox 2240. It too has a public interface comprised of a Boolean Variable Modifier MinFlag 2243 (which indicates whedier die window 2200 is minimized or not), point Variable Modifiers BoxRect TopLeft 2244 and BoxRect_BottomRight 2245 (which define die bounding rectangle of MinBox 2240), MinlCONDimensions 2246 and die height and widdi of die minimized icon, die Image Effect Modifier 2241 (which gives MinBox 2240 a bevelled appearance when clicked on), and Graphic Modifier 2242 (to set its color. Miniscript Modifier "CREATE MinBox" 2247 initializes MinBox 2240 at the beginning of Scene 2040 as follows: set MinFlag to false set width to 20 set height to 20 set BoxRectJTopLeft.x to BoundingRect_BottomRight.x - BoundingRectJTopLeft. x - widdi set BoxRectJTopLeft.y to 0 set BoxRectJBottomRight.x to BoxRectJTopLeft.x + width set BoxRect_BottomRight.y to BoxRectJTopLeft.y + height set position to BoxRectJTopLeft set MinlCONDimensions to (40,40) MinBox 2240 is initially maximized (as indicated by the flag being set to false), 20 pixels on a side, at die upper right hand corner of window 2200, widi an iconized state of 40 pixels on a side. MinMaxBehavior Modifier 2248 conu-ols the minimizing operation. Receipt of a mouse down within the bounding rectangle of MinBox 2240 causes Miniscript Modifier DetectMinBoxSelect 2249 to be executed: set MinFlag to not MinFlag send "MinBox Activated" widi MinFlag to element's parent The state of MinFlag 2243 is toggled and die message "MinBox Activated" is sent, along widi die new state of MinFlag 2243, to the parent of MinBox 2240, in a Relative Targeting fashion. This turns out to be die window 2200 itself. Thus, diis message triggers the two instances of MinMaxResponse 2207 and 2226 on window 2200 and TideBar 2200, respectively. As seen under MinMaxResponse 2207, diis aliased Behavior has two If Messenger Modifiers under it, "Max Response" 2208 and "Min Response" 2209. They each command the Element to be shown or hidden. Thus, window 2200 and TitleBar 2200 will either reappear or disappear when die MinBox 2240 is clicked. The receipt of the message "MinBox Activated" by MinMaxBehavior 2248 causes Miniscript Modifier "MinMax Response" 2250 to be invoked: if incoming = true dien set widdi to MinlCONDimensions.x set height to MinlCONDimensions.y set position.x to - (element's parent.position.x) set position.y to scene.height - element's parent.position.y - MinlCONDimensions.y else send "Scene Started" to element end if If MinFlag 2243 is true (as the incoming data), MinBox 2240 is minimized by setting its dimensions to the icon dimensions MinlCOND imens ions 2246, and is placed in die lower left hand corner of Scene 2040 (including calculations of die relative coordinates of Parent window 2200). If MinFlag 2243 is false, a "Scene Started" Environment Message is sent to me Element, which is a shorthand way to reinvoke die initialization Miniscript Modifier "Create MinBox" 2247. The window "Window X + MinMax + Drag" 2300 adds die dragging functionality to TitleBar 2320. MinBox 2340 is a passive beneficiary of diis dragging ability by virtue of its status as a child of window 2300, dius being dragged due to Hierarchical Relative Positioning. Its implementation is identical to MinBox 2240 (including all its contained Modifiers), and dius need not be repeated again. Also, Modifiers 2301-2307 and 2321-2326 are identical to Modifiers 2201-2207 and 2221-2226 (including any contained Modifiers), respectively, and need not be described again. The dragging ability is implemented through TitleBar DRAG Behavior 2327. Had TitleBar 2320 been the parent of window 2300 instead of its child, Hierarchical Relative Positioning would have handled die movement of window 2300 automatically. In any event, upon receiving a mouse down widiin TitleBar 2320, Messenger MouseDown 2329 sends a TitleBarMouseDown message to its 132 Element's parent, namely window 2300. Similarly, a successive mouse up event will cause the TideBarMouseUp message to be transmitted to window 2300. A mouse down also invokes die Miniscript Modifier CalcMouseOffset 2330, which calculates die offset, stored as point Variable MouseOffset 2328, between the mouse down and window 2300 positions. set MouseOffset to mouse - element's parent.position. Timer Messenger TitleBar MouseTracking 2331, which is respectively enabled and disabled by mouse downs and mouse ups, loops repeatedly widi no time delay (meaning no delay widiin die limits of idle cycling) and sends die message TitleBarMouseTracking widi MouseOffset 2328 as data. The primary purpose of the TitleBar Drag Behavior 2327 is to invoke die Window Drag Behavior 2308 between die TideBarMouseDown and TideBarMouseUp messages, through its Follow Mouse Miniscript Modifier 2309, whose simple script is as follows: set position to mouse - incoming. Thus, resetting the position of window 2300 in accordance widi MouseOffset 2328 (which was passed as data) brings die window 2300 into the position it would have been had it been dragged directly via a Drag Motion Modifier. Fig. 35(d) introduces die implementation of the alternative windowing system, namely that built upon Window X' 2400. It is virtually identical to Window X, particularly widi respect its use of Modifiers Name 2400, BoundingRectJTopLeft 2402, BoundingRect_BottomRight 2403, Graphic Modifier 2404, CREATE Window 2405, as well as Modifiers under TitleBar 2420. The sole difference is the lack of Image Effect Modifier 2105, and thus no beveling, as illustrated in Fig. 34(d). The window "Window X' + WindowShade" 2500 inttoduces the "window shade" feature, as seen in Fig. 35(e). Modifiers 2501-2505 and 2521-2525 are familiar incarnations of previous windows and need not be described again. The window shade feature is implemented dirough WinShadeBehavior 2526 which relies on Window WinShade Response 2506. Thus, Boolean Variable Modifier WinShadeFlag 2527 stores die window shade "state" (up=true, down=false) of window 2500, with Miniscript Modifier INITFlag 2529 simply initializing this state to false. The invocation of the window shade feature is accomplished by a double mouse click on TitleBar 2520. The DetectDoubleClick Behavior 2530 detects a double mouse click. An INITFlag Miniscript Modifier 2532 sets a Boolean Variable Modifier ClickFlag 2531 to false at the beginning of Scene 2040. Upon die detection of a Mouse Up event inside TitleBar 2520, the MouseUp Response Miniscript Modifier 2533 is run with die following script: if ClickFlag = true dien set WinShadeFlag to not WinShadeFlag send "WindowShadeActivated" with WinShadeFlag to element's parent set ClickFlag to false else set ClickFlag to true end if Thus, the state of ClickFlag 2531 is toggled. If it was true, die state of WinShadeFlag 2527 is toggled and sent wid message "WindowShadeActivated" to window 2500. Click Timer 2534 ttacks the maximum lengdi of time allowed in between single clicks of a double click, and is also invoked by die Mouse up event inside TitleBar 2520. When Clock Timer 2534 times out, it sends die message SingleClick, which invokes the SingleClick Miniscript Modifier 2535 which sets ClickFlag 2531 to false. In odier words, if MouseUpResponse 2533 is not invoked before SingleClick 2535 is u-iggered, dien die WindowShadeActivated message will not be sent. The WindowShadeActivated message is received by die "WINDOW WinShadeResponse" Behavior 2506, which eidier diggers the If Messenger "ShadeDown Response" 2507 which commands die window 2500 to show or die If Messenger "ShadeUp Response" 2508 which commands the window 2500 to hide, depending on the state of WinShadeFlag 2527 (transmitted as data). Finally, WinShade Sound 2528 provides a "window shading" sound effect, invoked when die TitleBar 2520 itself receives the WindowShadeActivated message, regardless of the state of WinShadeFlag 2527. Fig. 35(f) illustrates how easily die minimizing feature in window 2300 can be replaced by die window shade feature from window 2500 and integrated into window "Window X + WindowShade + Drag" 2600, despite die fact diat diey come from two different environments (analogous to two different "class hierarchies"). "WINDOW WinShadeResponse" 2607 replaces MinMaxResponse 2307, WinShadeBehavior 2626 replaces MinMaxResponse 2326 widiin TitleBar 2620, and MinBox 2340 is removed. All other Modifiers (2601-2606, 2608, 2621-2625 and 2627) continue to operate as do dieir counterparts in the previous windows. And the window 2600 somehow just "works". Though it utilizes MinBox 2340, Window 2600 (including its Window Drag Behavior 2308 and TitleBar Drag Behavior 2327) was not dependent on the existence of MinBox 2340. The fact diat messages no longer cascade down to a MinBox does not affect the operation of the window, unlike the situation in which an OOP superclass is replaced, causing its tightly coupled former subclass to "break" in an effort to locate the missing (inherited) mediods and data structures. Even had an explicit reference to a MinBox Modifier been left behind, this windowing system would not break. The affected Modifier would simply stop working until mis dependency was identified and resolved (a task that still would not require the audior to have access to the private data structures or methods of any object). Fig. 35(g) shows how a window ALL 2700 could in fact incorporate both die features of window 2300 and 2500, i.e. have die window shade as well as the minimize feature. With comparison to window 2600 in Fig. 35(f), the MinMaxResponse 2707 has returned under window 2700, as has MinMaxResponse 2726 under TitleBar 2720. MinBox 2740 has been reinttoduced, diough with die addition of a "MINBOX WinShadeResponse" Behavior 2749 identical in function to the Window WinShadeReponse 2708. All Modifiers 2701-2706, 2708, 2709, 2721-2728, and 2741-2748 again operate as do dieir counterparts in previous windows. In summary, this example illustrates the modularity of the Elements and Behaviors of die current invention. In one respect, diese object containers are quite independent of one anodier, relying on message broadcasting widiin die relatively narrow confines of die Su-uctural and Behavioral Hierarchies. Adding a new Behavior from a foreign environment often requires eidier no additional work or die relatively simple integration of a copy of an existing Behavior within an existing Element. Even where dependencies exist, they are evident from the surface (i.e. , the configuration of die Elements and Modifiers being transf erred), as opposed to being inextticably intertwined widi dieir former container environments, which often requires recompilation, access to third-party source code and, ultimately, fairly extensive programming. Although the invention has been described in detail widi reference to its presently preferred embodiments, it will be understood by one of ordinary skill in die art diat various modifications can be made, widiout departing from the spirit and die scope of die invention. Accordingly, it is not intended diat die invention be limited except as by me appended claims. 136

Claims: We claim: 1. An application development system comprising: (a) a first class of Element objects from which one or more Elements can be instantiated, die class defining a first set of characteristics inherent to each Element object in the class; (b) a second class of Modifier objects from which one or more Modifiers can be instantiated, die class defining a second set of characteristics inherent to each Modifier object in die class; (c) a first hierarchical linking mechanism that allows an audior to link a first instantiated Element from the first class as a parent to a first instantiated Modifier from the second class, die first instantiated Element attaining die second set of characteristics while the Element and Modifier remain linked; and (d) a second hierarchical linking mechanism that allows an audior to link the first instantiated Element as a parent to a second instantiated Element from the first class, die first instantiated Element providing an environmental frame of reference for the second instantiated Element and die first instantiated Modifier, but not attaining die second set of characteristics. 2. An application development system comprising: (a) a first class of Element objects from which one or more Elements can be instantiated, the first class defining a first set of characteristics inherent to each Element in die first class; (b) a second class of Modifier objects from which one or more Modifiers can be instantiated, die second class defining a second set of characteristics inherent to each Modifier in die second class; (c) a third class of Element objects from which one or more Elements can be instantiated, the third class defining a third set of characteristics inherent to each Element in the diird class; (d) a first hierarchical linking mechanism that allows a first Element instantiated from die first class to be linked to a first Modifier instantiated from 137 the second class, the first Element providing an environmental frame of reference for the first Modifier, and attaining the second set of characteristics, while the first Element and first Modifier remain linked; and (e) a second hierarchical linking mechanism that allows die first Element to be linked to a second Element instantiated from the diird class, the first Element providing an environmental frame of reference for the second Element while the first and second Elements remain linked, whereby die system allows for the creation of an object hierarchy. 3. The application development system of claim 2 wherein the first and third classes are equivalent. 4. An application development system comprising: (a) a first set of Elements sharing in common a first set of characteristics inherent to each member in the first set of Elements; (b) a second set of Modifiers sharing in common a second set of characteristics inherent to each member in the second set of Modifiers; (c) a third set of Elements sharing in common a third set of characteristics inherent to each member in the diird set of Elements; (d) a first hierarchical linking mechanism that allows a first Element from the first set of Elements to be linked to a first Modifier from the second set of Modifiers, die first Element providing an environmental frame of reference for the first Modifier, and attaining the second set of characteristics, while the first Element and first Modifier remain linked; and (e) a second hierarchical linking mechanism that allows die first Element from the first set of Elements to be linked to a second Element from die diird set of Elements, die first Element providing an environmental frame of reference for the second Element while the first and second Elements remain linked, whereby die system allows for the creation of a hierarchy of Elements and Modifiers. 138 5. The application development system of claim 4 wherein the first and third sets of Elements are equivalent. 6. The application development system of claim 2, 3, 4 or 5 wherein: (a) die first Element's set of characteristics includes a current position of die first Element; (b) e second Element's set of characteristics includes a current position of me second Element; and (c) die environmental frame of reference provided by die first Element is manifested at least in part by a Hierarchical Relative Positioning mechanism that determines me current position of the second Element relative to the current position of the first Element. 7. An application development system comprising: (a) a first class of Element objects from which one or more Elements can be instantiated, die first class defining a first set of characteristics inherent to each Element in the first class; (b) a second class of Modifier objects from which one or more Modifiers can be instantiated, the second class defining a second set of characteristics inherent to each Modifier in die second class; and (c) a hierarchical linking mechanism that allows an audior to link a first Element instantiated from the first class to a first Modifier instantiated from die second class, d e first Element attaining the second set of characteristics while die first Element and first Modifier remain linked, whereby die system allows a form of object-based authoring by enabling die modification of the behavior of an object widiout modifying die system's underlying class hierarchy. 8. An application development system comprising: (a) a first set of Elements sharing in common a first set of characteristics inherent to each member in the first set of Elements; 139 (b) a second set of Modifiers sharing in common a second set of characteristics inherent to each member in the second set of Modifiers; and (c) a hierarchical linking mechanism that allows an audior to link a first Element from the first set of Elements to a first Modifier from the second set of Modifiers, die first Element attaining the second set of characteristics while the first Element and first Modifier remain linked, whereby the system allows the behavior of an Element to be modified. 9. The application development system of claim 7 or 8 wherein: (a) the first Element's set of characteristics includes a current position of the first Element that is visually perceptible to a user of the system; and (b) die first Modifier's set of characteristics includes the ability to detect when die current position of die first Element crosses a predetermined boundary. 10. The application development system of claim 7 or 8 wherein the first Modifier's set of characteristics includes die ability to detect a collision between the first Element and anodier Element. 11. The application development system of claim 7 or 8 wherein: (a) the first Element constitutes a first object container containing the first Modifier while the first Element and first Modifier remain linked; and (b) die system can discern automatically dependencies of diat first object container. 12. The application development system of claim 11 wherein: (a) the first Element's set of characteristics includes a current position of die first Element; (b) the system furdier comprises a relative positioning mechanism that determines the current position of the first Element relative to a current position of an ancestor Element of the first Element; and 140 (c) the dependencies of die first object container include the current position of the first Element. 13. The application development system of claim 11 wherein: (a) the system furdier comprises an object configuration and messaging mechanism that allows die first Modifier to be configured to perform an action in response to the receipt of a specified message; and (b) the dependencies of die first object container include die specified message to which the first Modifier is configured to respond. 14. The application development system of claim 11 wherein: (a) the system furdier comprises Variable Modifiers having a diird set of characteristics inherent to each Variable Modifier, die third set of characteristics including die ability to store data on behalf of an Element; (b) the system further comprises an object configuration and variable scoping mechanism that allows die first Modifier to be configured to access a second Variable Modifier, provided diat the second Variable Modifier stores data on behalf of die first Element or an ancestor Element of die first Element; and (c) die dependencies of the first object container include die data stored by die second Variable Modifier. 15. An application development system comprising: (a) a first class of Element objects from which one or more Elements can be instantiated, die first class defining a first set of characteristics inherent to each Element in the first class; (b) a second class of Modifier objects from which one or more Modifiers can be instantiated, die second class defining a second set of characteristics inherent to each Modifier in die second class; and (c) a hierarchical linking mechanism that allows a first Element instantiated from the first class to be linked to a first Modifier instantiated from the second 141 class, the first Element providing an environmental frame of reference for the first Modifier while the first Element and first Modifier remain linked, whereby the system allows the behavior of an Element to be modified. 16. An application development system comprising: (a) a first set of Elements sharing in common a first set of characteristics inherent to each member in the first set of Elements; (b) a second set of Modifiers sharing in common a second set of characteristics inherent to each member in the second set of Modifiers; and (c) a hierarchical linking mechanism that allows a first Element from the first set of Elements be linked to a first Modifier from die second set of Modifiers, d e first Element providing an environmental frame of reference for the first Modifier while die first Element and first Modifier remain linked, whereby die system allows the behavior of an Element to be modified. 17. The application development system of claim 2, 4, 15 or 16 wherein: (a) the system furdier comprises a messaging mechanism that sends messages to Elements and Modifiers; and (b) die environmental frame of reference provided by the first Element is manifested at least in part by a Hierarchical Message Broadcasting mechanism that uses the messaging mechanism to broadcast a message sent to the first Element to descendants of the first Element. 18. The application development system of claims 2, 4, 15 or 16 wherein: (a) the system further comprises Variable Modifiers having a fourth set of characteristics inherent to each Variable Modifier, die fourth set of characteristics including die ability to store data on behalf of an Element; and (b) the environmental frame of reference provided by the first Element is manifested at least in part by a Hierarchical Variable Scoping mechanism that renders data stored in a Variable Modifier on behalf of die first Element accessible to descendants of die first Element. 142 96 31822 19. The application development system of claim 7, 8, 15 or 16 wherein: (a) the first Element's set of characteristics includes a current position and a graphic representation of the first Element that are visually perceptible to a user of the system; and (b) the first Modifier's set of characteristics includes die ability to change die current position of die first Element over time. 20. The application development system of claim 7, 8, 15 or 16 wherein: (a) the first Element's set of characteristics includes a graphic representation of the first Element that is visually perceptible to a user of die system; and (b) the first Modifier's set of characteristics includes graphic attributes that alter die first Element's graphic representation. 21. An application development system comprising: (a) a first class of Behavior objects from which one or more Behaviors can be instantiated, the first class defining a first set of characteristics inherent to each Behavior in die first class; (b) a second class of Modifier objects from which one or more Modifiers can be instantiated, die second class defining a second set of characteristics inherent to each Modifier in die second class; and (c) a hierarchical linking mechanism that allows a first Behavior instantiated from the first class to a first Modifier instantiated from the second class, die first Behavior providing an environmental frame of reference for the first Modifier while die first Behavior and first Modifier remain linked, whereby die system allows a behavioral hierarchy of Modifiers to be created. 22. An application development system comprising: (a) a first set of Behaviors sharing in common a first set of characteristics inherent to each member in the first set of Behaviors; (b) a second set of Modifiers sharing in common a second set of characteristics inherent to each member in the second set of Modifiers; and (c) a hierarchical linking mechanism that allows a first Behavior from the first set of Behaviors to be linked to a first Modifier from the second set of Modifiers, the first Behavior providing an environmental frame of reference for the first Modifier while the first Behavior and first Modifier remain linked, whereby die system allows a behavioral hierarchy of Modifiers to be created. 23. The application development system of claim 21 or 22 wherein: (a) die system furdier comprises a messaging mechanism mat sends messages to Behaviors and Modifiers; and (b) die environmental frame of reference provided by die first Behavior is manifested at least in part by a Hierarchical Message Broadcasting mechanism that uses the messaging mechanism to broadcast a message sent to the first Behavior to descendants of die first Behavior. 24. The application development system of claim 21 or 22 wherein: (a) die system further comprises Variable Modifiers having a fourth set of characteristics inherent to each Variable Modifier, the fourth set of characteristics including die ability to store data on behalf of a Behavior; and (b) die environmental frame of reference provided by the first Behavior is manifested at least in part by a Hierarchical Variable Scoping mechanism that renders data stored in a Variable Modifier on behalf of die first Behavior accessible to descendants of die first Behavior. 25. The application development system of claim 7, 8, 15, 16, 21 or 22 wherein the second set of characteristics includes die ability to send a message to another Modifier. 26. An application development system comprising: (a) a first class of Element objects from which one or more Elements can be instantiated, die first class defining a first set of characteristics inherent to each Element in the first class; 144 96/31822 (b) a second class of Modifier objects from which one or more Modifiers can be instantiated, the second class defining a second set of characteristics inherent to each Modifier in the second class; (c) a diird class of Behavior objects from which one or more Behaviors can be instantiated, the third class defining a third set of characteristics inherent to each Behavior in the diird class; (d) a fourth class of Modifier objects from which one or more Modifiers can be instantiated, die fourdi class defining a fourth set of characteristics inherent to each Modifier in die fourth class; and (e) a hierarchical linking mechanism mat allows: (1) linking of a first Element instantiated from the first class to a first Modifier instantiated from the second class and a first Behavior instantiated from the diird class; and (2) linking of die first Behavior to a second Modifier instantiated from the fourth class, wherein die first Behavior attains die fourth set of characteristics while die first Behavior and second Modifier remain linked, and die first Element attains the second, diird and fourdi sets of characteristics, while the first Element, first Behavior and first and second Modifiers remain linked, whereby die first, second, diird and fourth sets of characteristics define the first Element's personality. 27. An application development system comprising: (a) a plurality of object classes from which one or more objects can be instantiated, each class defining a set of characteristics inherent to each object in that class; and (b) a hierarchical linking mechanism that allows: (i) creation of a first object container by linking an instantiated first object having a first set of characteristics to an instantiated second object having a second set of characteristics, wherein the first object provides an 145 environmental frame of reference for the second object while die first and second objects remain linked; (ii) creation of a second object container by linking the second object to an instantiated diird object having a diird set of characteristics, wherein die second object provides an environmental frame of reference for the third object while die second and diird objects remain linked; and (iii) replacement of die second object widi an instantiated fourth object by breaking die links between the second object and the first and diird objects, and establishing corresponding links between the fourdi object and the first and diird objects, such that die first object provides an environmental frame of reference for the fourth object, which in turn provides an environmental frame of reference for the third object, while die first, diird and fourth objects remain linked, whereby die system allows for selective reusability of an object container and die objects it contains. 28. The application development system of claim 27 wherein die first, second, third and fourdi objects are Elements. 29. The application development system of claim 27 wherein the first and second objects are Elements, and the diird object is a Modifier, and wherein d e second object attains the diird set of characteristics while the second and diird objects remain linked. 30. The application development system of claim 27 wherein the first object is an Element, die second object is a Behavior and die third object is a Modifier, and wherein die first object attains the second and diird sets of characteristics while the first, second and third objects remain linked. 31. The application development system of claim 27 wherein the first and second objects are Behaviors, and die third object is a Modifier, and wherein die first object attains the second and third sets of characteristics while the first, second and diird objects remain linked. 32. An application development system comprising: (a) a plurality of object classes from which one or more objects can be instantiated, each class defining a set of characteristics inherent to each object in that class; and (b) a hierarchical linking mechanism that allows creation of: (i) a first object container by linking an instantiated first object having a first set of characteristics to an instantiated second object having a second set of characteristics, wherein the first object provides an environmental frame of reference for the second object while the first and second objects remain linked; and (ii) a second object container, replacing the first object widi an instantiated diird object having a diird set of characteristics, by breaking the link between the second object and die first object, and establishing a corresponding link between die second object and die third object, such diat die third object provides an environmental frame of reference for the second object while the objects remain linked, whereby die system allows selection of a new object container for an object. 33. The application development system of claim 32 wherein die first, second and diird objects are Elements. 34. The application development system of claim 32 wherein each of the first and third objects is either an Element or Behavior, and die second object is eidier a Behavior or Modifier. 35. The application development system of claim 32 wherein the dynamic object configuration and hierarchical linking mechanism allows configuration of the second object such diat the replacement of the first object widi the third object occurs dynamically, at runtime, upon the occurrence of a specified condition. 36. The application development system of claim 32 wherein the hierarchical linking mechanism further includes a touch-up mechanism that, upon die replacement of the first object with die diird object, automatically identifies and resolves dependencies of the first, second and third objects. 37. The application development system of claim 36 wherein the dependencies include a current position of die first and diird objects. 38. The application development system of claim 36 wherein the dependencies include a Variable accessed by die second object. 39. The application development system of claim 36 wherein the dependencies include a message to which the second object responds. 40. The application development system of claim 36 wherein: (a) the dependencies include a first asset constituting a dependency of die second object and a second asset constituting a dependency of die diird object, the system referencing each of the first and second assets both by a name and by a unique identifier; and (b) die touch-up mechanism, upon the replacement of the first object widi die third object, resolves name and unique identifier conflicts by: (i) replacing the unique identifier of die first asset with die unique identifier of die second asset, if the name of the first and second assets are equivalent; and (ii) assigning a new unique identifier to die first asset if die unique identifiers, but not die names, of the first and second assets are equivalent. 41. An application development system comprising: (a) a plurality of object classes from which one or more objects can be instantiated, each class defining a set of characteristics inherent to each object in that class; (b) a hierarchical linking mechanism that allows creation of: (i) a first object container, by linking an instantiated first object to an instantiated second object, wherein die first object provides an environmental frame of reference for the second object while the first and second objects remain linked; and (ii) a first object hierarchy within the first object container, by linking die second object to an instantiated diird object, thereby creating a second object container wherein the second object provides an environmental frame of reference for the third object while the second and third objects remain linked; and (c) a Hierarchical Message Broadcasting mechanism mat broadcasts a message sent to the first object container to the second and diird objects contained within the first object hierarchy, whereby the system allows the broadcasting of messages within an object hierarchy. 42. The application development system of claim 41 wherein: (a) die hierarchical linking mechanism further allows for linking of die first object to an instantiated fourth object, wherein die first object provides an environmental frame of reference for the fourdi object while die first and fourth objects remain linked; (b) die system furdier comprises an object configuration and messaging mechanism that allows die third object to be configured to send a message to a runtime object container that contains the diird object when die message is sent at runtime: and (c) if die first object is a runtime object container of bodi die diird and fourth objects, the message sent by the diird object to die first object will be broadcast to die fourth object by die Hierarchical Message Broadcasting mechanism, whereby an object can be configured to send a message to another object by relatively targeting the lowest common ancestor of the two objects. 43. The application development system of claim 41 further comprising an object configuration and messaging mechanism that allows an object to be configured to send a message to a specified destination Element and limit its broadcasting, via die Hierarchical Message Broadcasting mechanism, such that die message will not cascade to any Elements contained widiin the destination Element. 44. The application development system of claim 41 further comprising an object configuration and messaging mechanism that allows an object to be configured to send a message to a specified destination object and limit its broadcasting, via the Hierarchical Message Broadcasting mechanism, such that die message will not be relayed beyond die first object configured to respond to the message. 45. An application development system comprising: (a) a plurality of object classes from which one or more objects can be instantiated, each class defining a set of characteristics inherent to each object in that class; (b) a hierarchical linking mechanism that allows creation of an object container by linking an instantiated first object to an instantiated second object, wherein die first object provides an environmental frame of reference for the second object while die first and second objects remain linked; and (c) an object configuration and messaging mechanism mat allows configuration of die second object to send a message to a runtime object container that contains the second object when the message is sent at runtime, whereby the system allows the relative targeting of message destinations. 46. An application development system comprising: (a) a first class of Element objects from which one or more Elements can be instantiated, the first class defining a first set of characteristics inherent to each Element in die first class; (b) a second class of Modifier objects from which one or more Modifiers can be instantiated, die second class defining a second set of characteristics inherent to each Modifier in die second class; (c) a hierarchical linking mechanism that allows a first Element instantiated from the first class to be linked to a first Modifier instantiated from the second class, die first Element attaining the second set of characteristics while the first Element and first Modifier remain linked; and (d) a component API mat allows: (i) creation of a third class of Modifier objects, the third class defining a diird set of characteristics inherent to each Modifier in die third class; and (ii) integration of die diird class of Modifiers into die system such that die hierarchical linking mechanism can be used to link die first Element to a second Modifier instantiated from the diird class, wherein die first Element attains the diird set of characteristics while the first Element and second Modifier remain linked, whereby die system's component API allows the functionality of the system to be extended. 47. The application development system of claim 46 wherein the diird class is a subclass of die second class. 48. The application development system of claim 46 wherein: (a) me system further comprises a fourth class of Modifier objects from which one or more Modifiers can be instantiated, die fourth class constituting a subclass of die second class and inheriting at least some of the second set of characteristics, and defining a fourdi set of characteristics inherent to each Modifier in die fourdi class; and 151 (b) the component API further allows: (i) addition of one or more methods and data structures to the second class, via the component API, without access to or recompilation of source code defining die second class, diereby defining a supplemental set of characteristics, in addition to die second set of characteristics, inherent to each Modifier in the modified second class; and (ii) integration of the modified second class of Modifiers into the system such that die hierarchical linking mechanism can be used to link die first Element to a third instantiated Modifier from the fourdi class, wherein die first Element attains the supplemental set of characteristics, in addition to die fourdi set of characteristics, while the first Element and diird Modifier remain linked, whereby the system's component API allows the functionality of an existing superclass of the system to be extended. 49. An application development system comprising: (a) a first class of Element objects from which one or more Elements can be instantiated, die first class defining a first set of characteristics inherent to each Element in me first class; and (b) a media linking mechanism that allows: (i) linking of a first Element instantiated from the first class to a first media item having a first media data type, such diat die first Element will take on the appearance of die first media item during runtime while the first Element and first media item are linked; (ii) breaking of the link between the first Element and die first media item; and (iii) linking of the first Element to a second media item having a second media data type, such that the first Element will take on the appearance of die second media item during runtime while the first Element and second media item are linked, 152 96/31822 whereby the system allows an Element to be morphed among different media data types. 50. The application development system of claim 49 wherein die media linking mechanism further comprises an object configuration and dynamic linking mechanism that allows configuration of die first Element such mat the system dynamically, upon die occurrence of a specified runtime condition, breaks the link between die first Element and die first media item and establishes a link between the first Element and die second media item. 51. An application development system comprising: (a) a first class of Element objects from which one or more Elements can be instantiated, die first class defining a first set of characteristics inherent to each Element in the first class; (b) a second class of Element objects from which one or more Elements can be instantiated, die second class defining a second set of characteristics inherent to each Element in the second class; (c) a third class of Variable Modifier objects from which one or more Variables can be instantiated, die diird class defining a diird set of characteristics inherent to each Variable in die diird class, die third set of characteristics including the ability to store data on behalf of an Element; (d) an alias mechanism that allows an audior to create an alias of a first instantiated Variable having a first value, from which aliased copies of die first Variable can be made; and (e) a hierarchical linking mechanism that allows an instantiated first Element from the first class to be linked to a first aliased copy of die first Variable, and to link an instantiated second Element from the second class to a second aliased copy of die first Variable, such diat die first aliased copy of die first Variable stores the first value on behalf of the first Element, and die second aliased copy of the first Variable stores the first value on behalf of die second Element; 153 (f) wherein the alias mechanism causes any change at runtime to the first value stored by die first aliased copy of die first Variable to be reflected dynamically in the second aliased copy of the first Variable, such diat die first and second aliased copies of die first Variable store die same value at any give time during runtime, whereby the system provides dynamically aliased Variables. 52. An application development system comprising: (a) a first class of Element objects from which one or more Elements can be instantiated, die first class defining a first set of characteristics inherent to each Element in the first class; (b) a media linking mechanism that allows an instantiated first Element be linked to to a first media item having a eel-based animation data format, such that die Element will take on die appearance of the eels of the first media item at a specified animation rate during runtime; and (c) an object configuration and animation range selection mechanism that allows die first Element to be configured to play a specified range of eels of the first media item during runtime upon the occurrence of a specified condition, whereby die system allows dynamic changes to a portion of an animation that is played during runtime upon die occurrence of a specified condition. 53. An application development system comprising: (a) a plurality of object classes from which one or more objects can be instantiated, each class defining a set of characteristics inherent to each object in that class; and (b) a hierarchical linking mechanism that allows creation of: (i) a first object container in a first application, by linking an instantiated first object to an instantiated second object, wherein die first object provides an environmental frame of reference for the second object while die first and second objects remain linked; (ii) a first object hierarchy widiin the first object container, by linking the second object to an instantiated diird object, diereby creating a second object container wherein the second object provides an environmental frame of reference for the third object while die second and diird objects remain linked; and (iii) a diird object container in a second application, by linking an instantiated fourdi object to an instantiated fifth object, wherein die fourth object provides an environmental frame of reference for the fifth object while the fourdi and fifth objects remain linked; and (c) an object library mechanism that allows copying of: (i) the second object container from the first application into a first object library upon breaking the link between die first and second objects; and (ii) die second object container from the first object library into die second application, and linking of die fourdi object using die hierarchical linking mechanism, wherein the fourth object provides an environmental frame of reference for the second object container while the second, diird and fourdi objects remain linked, whereby die system allows for selective reusability of object containers across applications. 155

Inventors: FORSYTHE R HAMISH, GUDMUNDSON NORMAN K, LEE WAYNE A, FORSYTHE, R., HAMISH, GUDMUNDSON, NORMAN, K., LEE, WAYNE, A.
Applicants: FORSYTHE R HAMISH, GUDMUNDSON NORMAN K, LEE WAYNE A, MFACTORY INC, FORSYTHE, R., HAMISH, GUDMUNDSON, NORMAN, K., LEE, WAYNE, A., MFACTORY, INC.
Application year: 1996
Main classification: G06F9
IPC codes: G06F9, G06F17