Abstract:
A method, computer program product, and data processing system for facilitating the traversal of a hierarchy of GUI components containing components and/or containers from disparate GUI toolkits is disclosed. In a preferred embodiment, auxiliary associative data structures relating parent components in one toolkit to children in another toolkit are defined. When examining a component to determine if it has children, an appropriate associative data structure is consulted to determine if that component has a child from a disparate toolkit. In accordance with this preferred embodiment, additional associative data structures are defined, which also record the reverse “child-parent” relationship, so as to allow the GUI component tree to be traversed in both directions.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates generally to object-oriented graphical user interface technology. More specifically, the present invention is directed to a method for traversing a hierarchy of GUI components taken from disparate GUI toolkits.  
         [0003]     2. Description of the Related Art  
         [0004]     The earliest interactive computers relied on tele-typewriter (TTY) or text terminals for interactive communication with a human operator. These early forms of human-computer interaction (HCI) allowed for only text- or character- based information exchange. Many computer software products today utilize a graphical user interface or GUI (typically pronounced like “gooey” ). A GUI is visual means of human-computer interaction that utilizes pictures or other visual representations besides text or characters.  
         [0005]     Most GUIs make use of visual controls that are displayed on the user&#39;s display and actuated by user input. Typical visual controls include, but are not limited to, buttons, text fields (for entering text), radio buttons, checkboxes, selection boxes, and menu bars. In a typical GUI, a pointing device, such as a mouse, is used to move a cursor around a display and actuate visual controls. GUIs usually also make use of static display components, such as labels and icons, which are intended to be displayed, but generally have no input function, per se. Sometimes these static display components may serve an input role, however, when they are moved around on the display relative to other features on the display (e.g., dragging an icon of a file to a trash can icon to delete a file, for example).  
         [0006]     Many GUIs are what is known as a “windowing” interface, because they arrange information visually on a display in the form of panels or “windows” superimposed on a background called a “desktop.” In many systems, windows may be dragged to different locations on the display with a pointing device, enlarged, reduced, made to overlap with other windows. Typically, a window will contain a number of visual controls to allow a user to interact with a computer program by actuating the controls in the window. A special form of window, known as a “dialog box,” is displayed by a program when some input is required from a user.  
         [0007]     Windows, visual controls, and static display components are what are known as GUI components, because they are the building blocks that make up the GUI. Some GUI components, such as windows, are known as “container components” (or simply “containers”), because they may contain other components. For example, a window may contain visual controls, such as a button or menu bar, and static display components, such as text labels or icons. A container may also contain another container. For example, in some windowing-based word processors, the word processor itself occupies a (main) window, while each file under editing occupies another window within the main window.  
         [0008]     Container components include windows, but may also include other components, which may be visible or invisible. For example, the JAVA∩ programming language produced by Sun Microsystems, Inc. of Mountain View, Calif., defines various visible container components, such as windows and dialog boxes, as well as invisible container components, such as the “java.awt.Panel” container component, which is used solely to group a number of contained components into a single unit. Some examples of containers include, but are not limited to, windows, dialog boxes, panels, tabbed panels, notebook pages, and any other GUI components that have a capability of containing one or more other GUI components.  
         [0009]     The actual functionality for providing basic operations on GUI components, such as displaying the components or detecting user input directed at the components (e.g., from pointing at or clicking on a component with a pointing device), is often provided by system-level software, such as an operating system. Generally speaking, applications will issue calls to system-level software for creating and maintaining GUIs, while the system-level software detects user input events that are directed at particular GUI components and sends event notifications to the applications that are responsible for those GUI components.  
         [0010]     For example, the WINDOWS® operating system produced by Microsoft, Inc. of Redmond, Wash. provides services for the creation of GUIs and relaying of user input events to appropriate applications. The main interface for the WINDOWS® operating system itself is a GUI as well. In other settings, higher-level system software may operate on top of an operating system kernel (e.g., as a daemon or background process) to provide GUI services. For example, “X11” is an open-source GUI engine that operates as a process in an operating system. X11 adopts a client-server model in that an X11 server process accepts requests from applications (clients) for providing GUI services and relays user input events that pertain to particular GUI components to the applications associated with those components.  
         [0011]     Alternatively, an application may contain its own code for providing GUI services. Typically, this code will come in the form of a reusable code library for performing basic GUI operations.  
         [0012]     Many modern programming language implementations have built-in features for producing GUIs, usually either by providing an interface to GUI services provided by system-level software or by including libraries of low-level GUI code for which an interface in the programming language is provided. The JAVA™ programming language, for example, is an object-oriented programming language that includes standard application programming interfaces (APIs) for defining GUIs. Two APIs that are currently part of the JAVA™ programming language standard are the Abstract Windowing Toolkit (AWT) API and the Swing API (which is built on the AWT API). In the JAVA™ programming language, as is typical of object-oriented GUI APIs, each type of GUI component is defined as a class.  
         [0013]     In an object-oriented programming language, a class is a definition of a data type that includes a collection of data, called member variables, and a set of operations that may be performed on the data, called methods (or alternatively, member functions). An actual collection of data in the data type defined by a class is called an object. In object-oriented programming (OOP) parlance, an object is said to be an “instance” of the class, because it is a data structure that is defined in accordance with the class. The run-time process of generating an object in an object-oriented programming language is called “instantiation,” and an object that exists at run-time is said to be “instantiated.”  
         [0014]     Object-oriented programming languages also typically provide for what is known as “inheritance.” Using an inheritance a new class (called a “descendant” class) can be defined in terms of one or more existing classes (called “base” classes) so that the descendant class inherits one or more of the member variables or methods of the base class. For example, in the JAVA™ programming language&#39;s AWT API, “Container” is a descendant class of a base class called “Component,” the “Container” class will include at least some of the methods and member variables of “Container.” We thus say that “Container” is descended from “Component.” In many cases, a descendant class will include additional methods or member variables that are not inherited from the base class.  
         [0015]     Also, a descendent class may be written so as to override the base class&#39;s code for a particular method. For example, the base class “Container” may have a method called “show,” for displaying a GUI component, which the descendant class “Container” inherits. Since displaying a container (which may contain other components) is more specific than displaying a generic GUI component, the “Container” class may define different code for “show” than that of the “Component” class.  
         [0016]     This is important, since in most object-oriented languages, an object in a descendant class is treated as being a more specific instance of the base class. Thus, a “Container” object may be stored in a variable of type “Component,” or a method that takes a “Component” as an argument can also take a “Container” as an argument, since a “Container” will inherit characteristics (i.e., member variables and methods) from “Component.” This ability to treat objects from descendant classes as if they were instances of base classes is called “polymorphism.”  
         [0017]     In an object-oriented GUI API, such as those provided by the JAVA™ programming language, GUI components are instantiated as objects, and relationships are established between the instantiated objects in order to define the placement and behavior of GUI components with respect to each other. For example, a “containment relation” is a relationship between GUI components that relates a container component to the components contained by that container component. In the JAVA™ programming language, for example, a component typically enters into a containment relation with a container through a method of the container called “add.”  
         [0018]     A typical GUI component has one or more attributes that define particular properties of the component. For example, a “button” component in a typical windowing GUI will have attributes that define the size of the button on the display, the text or graphics displayed on the face of the button, the background color of the button, a keyboard shortcut associated with the button, and the like. In general, the portion of program code (e.g., function, method, subroutine, procedure, etc.) that instantiates a GUI component will also contain a number of lines of code that set the attributes for that component to desired values. In the JAVA™ programming language and other object-oriented programming systems, for example, components generally have methods that can be executed to set particular attributes of the component.  
         [0019]     “Eclipse” is an open-source software platform and API, written in JAVA, that is designed to facilitate the creation of integrated development environments (IDEs). IDEs typically combine a text editor with various software development tools, such as compilers, linkers, debuggers, profilers, and the like through a unified user interface. The Eclipse platform, not surprisingly, provides its own support for creating GUIs. The Eclipse API includes a GUI toolkit called the “Standard Widget Toolkit,” or “SWT” for short. SWT has a similar object-oriented structure to AWT.  
         [0020]     It is possible to use components from both the AWT and SWT toolkits in a single GUI. The Eclipse API includes a class called “SWT_AWT,” which includes methods that allow one to create a child component/container in one toolkit for association with a parent component/container in the other toolkit. The method “SWT —AWT.new _Frame,” for instance, allows one to create a “Frame” container in the JAVA™ AWT that is associated with a parent container (called a “Composite”) in the SWT. Likewise, “SWT —AWT.new _Shell” allows one to create a “Shell” container in the SWT that is associated with a parent “Container” (intentionally capitalized) in the JAVA™ AWT. Eclipse does not, however, provide a way to take a container in one toolkit and access its children that are in the other toolkit. This makes it impossible to fully traverse a GUI component tree that contains components/containers from both toolkits.  
         [0021]     What is needed, therefore, is method and system to allow a GUI component tree containing components/containers from multiple toolkits to be traversed. The present invention provides a solution to these and other problems, and offers other advantages over previous solutions.  
       SUMMARY OF THE INVENTION  
       [0022]     The present invention provides a method, computer program product, and data processing system for facilitating the traversal of a hierarchy of GUI components containing components and/or containers from disparate GUI toolkits. In a preferred embodiment, auxiliary associative data structures relating parent components in one toolkit to children in another toolkit are defined. When examining a component to determine if it has children, an appropriate associative data structure is consulted to determine if that component has a child from a disparate toolkit. In accordance with this preferred embodiment, additional associative data structures are defined, which also record the reverse “child-parent” relationship, so as to allow the GUI component tree to be traversed in both directions.  
         [0023]     As one skilled in the art will recognize, the teachings of the present invention may be applied whenever a hierarchy of objects or data structures must be constructed from incompatible types, such that an object in one type is incapable of recognizing that it has a child of a different type. Thus the invention has wide application in a variety of problem domains.  
         [0024]     The foregoing is a summary and thus contains, by necessity, simplifications, generalizations, and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the present invention, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth below.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings, wherein:  
         [0026]      FIG. 1  is a UML class diagram illustrating relationships between GUI component and container classes in the two GUI toolkits utilized in a preferred embodiment of the present invention;  
         [0027]      FIG. 2  is a diagram illustrating a tree of GUI components from multiple GUI toolkits in accordance with a preferred embodiment of the present invention;  
         [0028]      FIG. 3  is a diagram illustrating associative data structures utilized in a preferred embodiment of the present invention;  
         [0029]      FIG. 4  is a flowchart representation of a process of generating a cross-toolkit embedded GUI component in accordance with a preferred embodiment of the present invention;  
         [0030]      FIG. 5  is a flowchart representation of a process of traversing a GUI component tree in accordance with a preferred embodiment of the present invention; and  
         [0031]      FIG. 6  is a block diagram of a data processing system in which a preferred embodiment of the present invention may be implemented.  
     
    
     DETAILED DESCRIPTION  
       [0032]     The following is intended to provide a detailed description of an example of the invention and should not be taken to be limiting of the invention itself. Rather, any number of variations may fall within the scope of the invention, which is defined in the claims following the description.  
         [0033]      FIG. 1  is a simplified/abbreviated class diagram in Unified Modeling Language (UML) illustrating relationships between GUI component and container classes in the two GUI toolkits utilized in a preferred embodiment of the present invention (AWT and SWT). The base class of GUI component in the JAVA™ AWT is “java.awt.Component” class  102 . AWT containers, which themselves are components (by virtue of being subclasses of “java.awt.Component” class  102 ), are represented by “java.awt.Container” class  104 . “java.awt.Container” class  104  includes a built-in method “getcomponents()”  105 , which returns an array containing the AWT component children of the container (the children being instances of “java.awt.Component” class  102 ). Note that there is no built-in method to “java.awt.Container” class  104  to allow one to examine children components of an AWT container that are defined in a different toolkit from AWT (such as SWT). Further subclasses of “java.awt.Container” class  104  include “java.awt.Window” class  106  and its subclass “java.awt.Frame” class  108 , which are used to represent visible windows in the JAVA™ AWT.  
         [0034]     The SWT, included in Eclipse, defines analogous classes for constructing object-oriented GUIs.  
         [0035]     “org.eclipse.swt.widgets.Control” class  110  is the base class for GUI components in SWT and is analogous to “java.awt.Component” class  102  in the standard JAVA™ AWT API.  
         [0036]     “org.eclipse.swt.widgets.Composite” class  112  is a subclass of “org.eclipse.swt.widgets.Control” class  110  and is the base container class for GUI components in SWT, much as “java.awt.Container” class  104  is the base container class for GUI components in AWT. In a similar manner to “java.awt.Container” class  104 , “org.eclipse.swt.widgets.Composite” class  112  includes a built-in method “getChildren()”  113 , which returns an array containing the SWT component children of the container (the children being instances of “org.eclipse.swt.widgets.Control” class  110 ). Just as with “java.awt.Container” class  104 , there is no built-in method to “org.eclipse.swt.widgets.Composite” class  112  to allow one to examine children components of an SWT container that are defined in a different toolkit from SWT (such as AWT). Further subclasses of “org.eclipse.swt.widgets.Composite” class  112  include “org.eclipse.swt.widgets.Canvas” class  114  and its subclass “org.eclipse.swt.widgets.Decorations” class  116 .  
         [0037]     “org.eclipse.swt.widgets.Shell ” class  118  is a subclass of “org.eclipse.swt.widgets.Decorations” class  116  and is are used to represent visible windows in SWT, much as “java.awt.Frame” class  108  is used to represent visible windows in AWT.  
         [0038]     “org.eclipse.swt.awt.SWT_AWT” class  120  forms a sort of “bridge” between the two GUI toolkits.  
         [0039]     “org.eclipse.swt.awt.SWT_AWT” class  120  includes methods “new_Frame()”  121  and “new_Shell()”  123 , which allow one to create a child component/container in one toolkit for association with a parent component/container in the other toolkit. “new_Frame()” method  121  generates (relationship  122 ) a Frame container (“java.awt.Frame” class  108 ) in the JAVA™ AWT that is associated with an SWT Composite (“org.eclipse.swt.widgets.Composite” class  112 ) as its parent container. The parent Composite object is passed into “new_Frame()” method  121  as an argument to allow this parent-child relationship to be created. Likewise, “new_Shell()” allows one to create a “Shell” container (“org.eclipse.swt.widgets.Shell ” class  118 ) in SWT that is associated with a parent “Container” (“java.awt.Container” class  104 ) in the JAVA™ AWT.  
         [0040]      FIG. 2  is a diagram illustrating a tree  200  of GUI components from multiple GUI toolkits in accordance with a preferred embodiment of the present invention. Root component  202  is defined as an SWT component and has children  204 ,  206 , and  208  that are also SWT components. SWT component  206 , however, has a child component  210  that is from the AWT toolkit.  
         [0041]     AWT component  210  was defined by calling the “new_Frame()” method of the SWT_AWT class, which is part of the Eclipse API. “new_Frame()” takes a parent SWT component as an argument creates a new AWT “Frame” container object that is a child of the parent SWT component. Thus, in the example provided in  FIG. 2 , “new_Frame()” was called with SWT component  206  as an argument. This resulted in AWT component  210  being created and associated with SWT component  206  as the child of SWT component  206 . This relationship (parent-child relationship  209 ) is represented by a dashed line in  FIG. 2 . AWT component  210  has its own children  212 ,  214 , and  216 , which are AWT components, like AWT component  210 . A preferred embodiment of the present invention is directed to a method for traversing a tree structure such as component  200 , where there exists a parent-child relationship between components from different GUI toolkits (e.g., parent-child relationship  209 ) in  FIG. 2 .  
         [0042]      FIG. 3  is a diagram illustrating associative data structures utilized in a preferred embodiment of the present invention. Associative data structure  300  associates parent components in SWT (denoted by column  302 ) with child components in AWT (denoted by column  304 ). Thus, to determine the AWT child component of an SWT component, the SWT component is used as a key to look up the entry (i.e., the row in  FIG. 3 ) associated with that SWT parent component (in column  302  in  FIG. 3 ), which reveals the corresponding child component (in column  304 ). In a preferred embodiment of the present invention, two such parent-child associative data structures will be defined: one that maps SWT parents into AWT children (shown as associative data structure  300  in  FIG. 3 ) and another that maps AWT parents into SWT children (not shown).  
         [0043]     In an actual embodiment of the invention, associative data structure  300  may be implemented using one of the built-in data structures provided for in the JAVA™ API, such as java.util.Hashtable (from JAVA™ 1.0) or the later java.util.Map classes, such as java.util.HashMap (which, internally, implements an associative data structure as a hash table) and java.util.TreeMap (which, internally, implements an associative data structure as a binary tree). One skilled in the art will recognize that any of a number of known types of associative data structures may be utilized to implement associative data structure  300  without limitation and without departing from the scope and spirit of the present invention. Since JAVA™ refers to objects by reference, references to the actual GUI components themselves may be stored in the associative data structure.  
         [0044]     In an alternative embodiment, a separate “set” or “collection” data structure is used to store the set of “keys” in the associative data structure. For instance, in the case of associative data structure  300 , this separate “set” data structure would store (or, more accurately, store references to) the set of SWT parent objects in column  302 . In the JAVA™ language, this data structure may be readily implemented using a java.util.Set data structure, although those skilled in the art will recognize that other data structures may be utilized, without limitation and without departing from the scope and spirit of the present invention.  
         [0045]     One skilled in the art will recognize, however, that it is not strictly necessary (at least in the JAVA™ language) to store the set of keys in a separate data structure. In one particular embodiment of the present invention, for example, the associative data structure is stored as a java.util.Map data structure (such as a java.util.HashMap), in which case the set of keys may be obtained simply by calling the “keySet()” method of the java.util.Map structure. Alternatively, one may check to see if a given key exists in the java.util.Map data structure by simply calling the method “containsKey(Key),” where “Key” is the key being checked for.  
         [0046]     As shown in  FIG. 3 , a preferred embodiment of the present invention also includes a child-parent associative data structure  301 , which performs the reverse mapping to associative data structure  301 , mapping AWT children (column  306 ) to SWT parents (column  308 ). As with parent-child associative data structure  300 , a preferred embodiment will also include a child-parent associative data structure that maps SWT children to AWT parents (not shown).  
         [0047]     In another possible embodiment, the data structures utilized for maintaining the parent-child relationships need not necessarily be associative data structures, per se. For example, a simple list might be used to store parent-child (and child-parent) relationships, where the location of the appropriate object to be identified can be determined without first performing a key lookup. For example, if each component has a unique ID number (called “N,” for instance), then the corresponding parent or child might be located in an array or list by looking for the “Nth” item in the list or array.  
         [0048]      FIG. 4  is a flowchart representation of a process of generating a cross-toolkit embedded GUI component in accordance with a preferred embodiment of the present invention utilizing the JAVA™ AWT and Eclipse SWT GUI toolkit APIs. First, one of the methods of the SWT_AWT class (either new_Frame or new_Shell) is called to generate a GUI component from one toolkit (an AWT Frame or an SWT Shell, respectively) that is a child of a parent object from the other GUI toolkit (Eclipse SWT or JAVA™ AWT, respectively) (block  400 ). After the child GUI component has been created, the parent-child relationship is stored in an appropriate associative data structure, as depicted with respect to associative data structure  300  in  FIG. 3 , for example (block  402 ). Finally, the reverse association (child-parent) is registered in an appropriate associative data structure (e.g., associative data structure  301  in  FIG. 3 ) (block  404 ).  
         [0049]      FIG. 5  is a flowchart representation of a process of traversing a GUI component tree in accordance with a preferred embodiment of the present invention. In this preferred embodiment, it is assumed that if a parent component has a child component from a different toolkit, then the parent component will have no child components from the same toolkit as the parent, although one skilled in the art will recognize that it is possible to implement an embodiment of the present invention without this assumption/restriction. Considering the “current node” in the GUI component tree (initially the root element of the tree) (block  500 ), a determination is made as to whether that current node has children from the same GUI toolkit (block  502 ). For instance, if the current node comes from the JAVA™ AWT, a determination is made as to whether the current node has children that are AWT components, and if the current node comes from the Eclipse SWT, a determination is made as to whether the current node has children that are SWT components. As previously mentioned, the toolkits themselves have methods to allow this determination to be made (e.g., AWT containers have methods that allow the existence of other AWT component children to be determined). If the current node has children from the same GUI toolkit (block  502 :Yes), then the tree traversal continues by considering each of the children (block  504 ) and the process cycles back to block  500 . One skilled in the art will recognize that the particular order in which the children are considered may vary (according to the type of tree traversal being performed) without departing from the scope and spirit of the present invention. For example, the process described in  FIG. 5  may be used to perform a depth-first traversal, breadth-first traversal, or other form of tree traversal, without limitation.  
         [0050]     If, on the other hand, the current node does not have children from the same GUI toolkit (block  502 :No), a determination is then made as to whether the current node has an entry in a parent-child associative data structure (e.g., associative data structure  300  in  FIG. 3 ) (block  506 ). If so (block  506 :Yes), then the corresponding child component for the current node (which will be from a different GUI toolkit than the current node) is identified from the associative data structure (block  508 ). The tree traversal process then continues with that child component (block  510 ) and the process cycles back to block  500 .  
         [0051]     If, on the other hand, the current node does not have a corresponding entry in a parent-child associative data structure (block  506 :No), then the current node must be a leaf node in the GUI component tree, in which case no deeper traversal of the tree can be performed from the current node. In  FIG. 5 , this leaf node condition is symbolized by progressing to “end” block  512 , since a recursive subroutine for traversing a tree would exit at this point. However, as one skilled in the art will recognize, the fact that the subroutine ends or exits at this point does not mean that the entire tree traversal ends at this point. Additional traversal may take place starting from a higher-level (less deep) level of the tree, due to the recursive nature of the subroutine. Those skilled in the art will recognize that the process described in  FIG. 5  may also be performed without using recursive subroutine calls by utilizing a stack or other similar data structure for keeping track of the current position within the tree, as is widely known in the art. This non-recursive implementation may be utilized in programming languages that do not have built-in support for recursion, such as Fortran-77 or most assembly languages.  
         [0052]      FIG. 6  illustrates information handling system  601 , which is a simplified example of a computer system capable of performing the computing operations of the host computer described herein with respect to a preferred embodiment of the present invention. Computer system  601  includes processor  600  which is coupled to host bus  602 . A level two (L2) cache memory  604  is also coupled to host bus  602 . Host-to-PCI bridge  606  is coupled to main memory  608 , includes cache memory and main memory control functions, and provides bus control to handle transfers among PCI bus  610 , processor  600 , L2 cache  604 , main memory  608 , and host bus  602 . Main memory  608  is coupled to Host-to-PCI bridge  606  as well as host bus  602 . Devices used solely by host processor(s)  600 , such as LAN card  630 , are coupled to PCI bus  610 . Service Processor Interface and ISA Access Pass-through  612  provides an interface between PCI bus  610  and PCI bus  614 . In this manner, PCI bus  614  is insulated from PCI bus  610 . Devices, such as flash memory  618 , are coupled to PCI bus  614 . In one implementation, flash memory  618  includes BIOS code that incorporates the necessary processor executable code for a variety of low-level system functions and system boot functions.  
         [0053]     PCI bus  614  provides an interface for a variety of devices that are shared by host processor(s)  600  and Service Processor  616  including, for example, flash memory  618 . PCI-to-ISA bridge  635  provides bus control to handle transfers between PCI bus  614  and ISA bus  640 , universal serial bus (USB) functionality  645 , power management functionality  655 , and can include other functional elements not shown, such as a real-time clock (RTC), DMA control, interrupt support, and system management bus support. Nonvolatile RAM  620  is attached to ISA Bus  640 . Service Processor  616  includes JTAG and I2C buses  622  for communication with processor(s)  600  during initialization steps. JTAG/I2C buses  622  are also coupled to L2 cache  604 , Host-to-PCI bridge  606 , and main memory  608  providing a communications path between the processor, the Service Processor, the L2 cache, the Host-to-PCI bridge, and the main memory. Service Processor  616  also has access to system power resources for powering down information handling device  601 .  
         [0054]     Peripheral devices and input/output (I/O) devices can be attached to various interfaces (e.g., parallel interface  662 , serial interface  664 , keyboard interface  668 , and mouse interface  670  coupled to ISA bus  640 . Alternatively, many I/O devices can be accommodated by a super I/O controller (not shown) attached to ISA bus  640 .  
         [0055]     In order to attach computer system  601  to another computer system to copy files over a network, LAN card  630  is coupled to PCI bus  610 . Similarly, to connect computer system  601  to an ISP to connect to the Internet using a telephone line connection, modem  675  is connected to serial port  664  and PCI-to-ISA Bridge  635 .  
         [0056]     While the computer system described in  FIG. 6  is capable of supporting the instruction set architecture described herein, this computer system is simply one example of a computer system. Those skilled in the art will appreciate that many other computer system designs are capable of performing the processes described herein.  
         [0057]     Those skilled in the art will also recognize that the teachings of the present invention may be applied in contexts other than just GUI toolkits. The invention may be utilized in any situation in which a hierarchy of incompatible types must be defined. For example, one may wish to create a hierarchy in which a GUI component is the parent of a DOM (Document Object Model) of an HTML (HyperText Markup Language) page, in order to represent the display of that page within a GUI component such as a window. Other possible implementations need not involve GUI components at all, as one skilled in the art will recognize that many different types of essentially incompatible objects and data structures may be arranged hierarchically, thus creating a problem domain in which the bridging techniques of the present invention may be applied.  
         [0058]     One of the preferred implementations of the invention is a client application, namely, a set of instructions (program code) or other functional descriptive material in a code module that may, for example, be resident in the random access memory of the computer. Until required by the computer, the set of instructions may be stored in another computer memory, for example, in a hard disk drive, or in a removable memory such as an optical disk (for eventual use in a CD ROM) or floppy disk (for eventual use in a floppy disk drive), or downloaded via the Internet or other computer network. Thus, the present invention may be implemented as a computer program product for use in a computer. In addition, although the various methods described are conveniently implemented in a general purpose computer selectively activated or reconfigured by software, one of ordinary skill in the art would also recognize that such methods may be carried out in hardware, in firmware, or in more specialized apparatus constructed to perform the required method steps. Functional descriptive material is information that imparts functionality to a machine. Functional descriptive material includes, but is not limited to, computer programs, instructions, rules, facts, definitions of computable functions, objects, and data structures.  
         [0059]     While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects. Therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. Furthermore, it is to be understood that the invention is solely defined by the appended claims. It will be understood by those with skill in the art that if a specific number of an introduced claim element is intended, such intent will be explicitly recited in the claim, and in the absence of such recitation no such limitation is present. For non-limiting example, as an aid to understanding, the following appended claims contain usage of the introductory phrases “at least one” and “one or more” to introduce claim elements. However, the use of such phrases should not be construed to imply that the introduction of a claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an;” the same holds true for the use in the claims of definite articles.