Abstract:
In an interface-based binary object system capable of supporting multiple interfaces into objects created by class templates, a relationship is defined as a pair of complementary collections on two separate interfaces, each interface found on separate objects. A link between objects is formed when an interface of one object lists an object supporting the related interface included in the object and vice versa. The collections may be of objects supporting the related interfaces or may be of specific relationship objects leading to objects supporting the related interfaces. The collections are potentially multi-valued entities that enable relationships to be established between objects according to one-to-one, many-to-one, and many-to-many architectures. By implementing a specific relationship object, behavior may be imparted to the relationship itself thereby providing more robust system behavior. Objects thus linked can be easily traversed so that convenient navigation models can be implemented allowing clients quick access to desired objects by navigating through relationships between objects.

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 08/822,449, filed Mar. 19, 1997 now U.S. Pat. No. 6,035,342 entitled “Method and Computer Program Product for Implementing Object Relationships,” which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     This invention relates to the field of object-oriented databases wherein navigation between objects is a fundamental method for finding desired data. More specifically, this invention relates to the methods and structures for creating relationships between software objects in order to assist in object navigation. 
     2. Present State of the Art 
     Object-oriented systems, including databases, have become prevalent in recent years as a significant design technique that allows high degrees of code reusability between projects and for modeling real world solutions to problems in a more natural way. A software object is composed of data and methods to operate on or manipulate the data and otherwise give the object its “behavior.” 
     In many database applications, it is useful to create a relationship between objects so that a client may navigate from one object to another based on the relationship. The usefulness of relationship navigation derives in part from the different types of objects and their arrangement with respect to one another in forming “models” as part of an implemented software solution. For example, software objects used to present the various pieces in a development environment database would tend to have some very natural relationship. In such a database, an object representing a C++ source file would be related to other objects representing header files and to compiled code generated from the source file. 
     Relationships allow focused navigation through an object database. For example, a client testing the current state of a completed application in the development environment database would traverse or navigate the relationships between the objects representing the constituent parts to determine which modules would require recompilation or other action. 
     Furthermore, searches may be made on specific types of relationships to identify objects having a particular characteristic in the structured hierarchy of related objects. The relationship itself becomes an attribute that distinguishes the object. 
     In some database applications, it is only the state of an object that is stored in a repository. A software client will access the object state by instantiating an object having the assigned state and manipulate the object in order to operate on that state. Other objects may be instantiated as necessary through object methods to gain access to other object states and for navigating through the database. The key to navigating the database are methods that will instantiate necessary objects to traverse relationships between related objects. By allowing relationships between objects, structure is added to a database of objects and hence greater meaning can be given to the objects and the information represented therein. This allows object-oriented databases to more closely mimic structure and relationships found in the real world problems that object-oriented software products are intended to model. 
     Currently, relationships or links between objects are made on the entire object, usually defined in the class used to create the object upon instantiation. While this allows relationships to exist between objects, it lacks granularity for allowing objects of different types to be conventionally related without minimizing object functionality or increasing object overhead. 
     Ways are often sought to present an intuitive model for incrementally adding functionality into objects. One successful approach has been an object system where each object is composed of multiple interfaces, each interface representing a quantum of related functionality. An object is built of necessary interfaces for giving the object the desired character or behavior. It would be advantageous to incorporate relationship behavior on such interfaces to thereby allow interfaces to define relationships rather than object classes. 
     Methods of creating, managing, and defining object relationships are sought that increase system efficiency, expand potential functionality, are easily extensible, and otherwise add capabilities to object oriented designs. Those methods that allow greater flexibility and the ability to easily relate objects of different types (i.e., those created or instantiated by different classes) to be easily related based on object characteristics rather than the mechanical creation mechanisms are particularly important. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     It is an object of the present invention to relate two separately instantiated objects through a logical link. 
     It is another object of the present invention to provide a navigation mechanism between related objects. 
     It is a further object of the present invention in some embodiments to represent relationships between objects as separate objects themselves so that behavior may be attributed to such relationship objects. 
     It is an object of the present invention to relate objects based on characteristics of the related objects rather than simply the class of the object, thereby allowing objects of different types to be easily related. 
     Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. 
     To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a method and computer program product for implementing object relationships is provided. 
     A relationship is a connection between two objects and is a useful construct for traversing through related objects in an object oriented database or persistent object repository. The present invention is directed to a novel method and program code product for implementing an object relationship in a persistent object repository that stores object states. This is done by defining a relationship as a pair of complementary collections on two separate interfaces, each interface found on separate objects. 
     A link between objects is formed when an interface of one object lists an object supporting the related interface included in the latter object and vice versa. The collections may be of objects supporting the related interfaces or may be of specific relationship objects leading to objects supporting the related interfaces. By implementing a specific relationship object, behavior may be imparted to the relationship itself. 
     By defining the relationship on an interface of an object rather than the class of the object, objects of different types created by different classes may be easily related based on the same kind of relationship, due to the different classes supporting the same interface. This creates a more intuitive model since it is object characteristics (as defined by interfaces) that provide functional capabilities to clients rather than mechanisms such as class definitions used to create or instantiate an object. 
     In a first embodiment, the link between objects is formed when a collection on one interface of one object contains direct references to the related objects supporting the related interface. Correspondingly, a collection exists on objects having the former interface listing related objects supporting the latter interface. Generally, a collection pair relating or linking particular interfaces (and hence the objects supporting those interfaces) has an origin object associated with an origin interface and a destination object associated with a destination interface. 
     In a second embodiment, each of the collections described previously in connection with the first embodiment is implemented as a specific collection object that may be accessed by a method on an interface of the related objects (origin or destination). This implementation allows more generic navigation models and behavior may be extended from the collection object to implement custom behavior. 
     In a third embodiment, each of the collection objects described previously in connection with the second embodiment implements a collection of relationship objects that can be used to arrive at the actual related objects supporting the related interface. When implementing a relationship through relationship objects, specific behavior may also be implemented on the relationship object and extended as necessary according to the binary extensibility scheme of the underlying object model. 
     In a fourth embodiment, the facilities of both the second and third embodiments are combined so that a user has both options available. The more direct collection of objects supporting the related interface provides a more efficient and convenient link when only the related object is desired, while the collection of relationship objects allows behavior to be associated with the relationship itself. Again, both collections on the origin and destination objects are implemented by objects (e.g., one object for each collection) themselves. 
     In a fifth embodiment, a single collection object is implemented that in turn has the facilities for managing collections of related objects having the related interface, and relationship objects leading to related objects supporting the related interface. In this manner, a single collection object may be accessed by an origin or destination object rather than requiring two separate collection objects as shown in the fourth embodiment. 
     These embodiments showing implementation variations of the present invention have differing characteristics in terms of extensibility to add custom behavior, performance, and complexity. A designer will choose the embodiment that best suits the application and those skilled in the art may yet see other embodiments that incorporate the present invention. 
     These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the manner in which the above-recited and other advantages and objects of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. These drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
     FIGS. 1A and 1B are logical diagrams showing the relationship between classes, interfaces, properties, objects, and clients. More particularly, FIG. 1A shows a plurality of classes for use as templates to create instantiated objects with each class implementing or supporting one or more interfaces. FIG. 1B shows a client that is accessing or interacting with three objects created by the classes in FIG.  1 A through the defined interfaces. 
     FIG. 2 is a logical diagram depicting the class, interface, and relationships for an address book example that has an address book class and a contact class. 
     FIG. 3 is a diagram showing the values for a number of contacts and address books according to the logical model in FIG.  2 . Specifically, the property information for five contacts and two address books is shown. 
     FIG. 4 is a logical drawing showing how the address book example as defined in FIG. 2 with the data of FIG. 3 would appear in terms of instantiated objects and relationships between those instantiated objects. 
     FIGS. 5A and 5B are terminology diagrams to explain how the objects would be related based on interfaces. FIG. 5A is a generic terminology diagram while FIG. 5B illustrates the Contains relationship in the address book example as shown graphically in FIG.  3 . 
     FIGS. 6A and 6B are object diagrams illustrating one embodiment of the present invention wherein a direct collection on the origin and destination objects is used to implement the relationship between objects. FIG. 6A shows the relationship between objects in more detail while FIG. 6B shows the address book example of FIG. 4 as it would appear with relationships implemented using the embodiment of FIG.  6 A. 
     FIGS. 7A and 7B are object diagrams illustrating another embodiment of the present invention wherein separate collection objects associated with the origin and destination objects to implement the collection of related objects. FIG. 7A shows the relationship in more detail while FIG. 7B shows how the address book example of FIG. would appear with relationships implemented according to the embodiment of FIG.  7 A. 
     FIGS. 8A and 8B are object diagrams illustrating another embodiment of the present invention wherein collections of separate relationship objects are used to implement a relationship between objects. FIG. 8A shows the relationship implementation in detail while FIG. 8B shows the address book example FIG. 4 as it would appear with relationships implemented according to the embodiment of FIG.  8 A. 
     FIGS. 9A and 9B are object diagrams illustrating another embodiment of the present invention that utilizes two collections with each object; one indicating the target objects, and the other indicating relationship objects. This embodiment effectively combines the embodiments shown in FIGS. 7A and 7B and the embodiment shown in FIGS. 8A and 8B. FIG. 9A shows the relationship as implemented in detail while FIG. 9B shows how the address book example of FIG. 4 would appear with relationships implemented according to the embodiment of FIG.  9 A. 
     FIGS. 10A and 10B are object diagrams showing another embodiment of the present invention wherein a single hybrid collection object that will represent a collection of target objects and relationship objects in order to implement a relationship according to the present invention. FIG. 10A shows the relationship in detail while FIG. 10B shows the address book example of FIG. 4 as it would appear with the relationships implemented according to the embodiment of FIG.  10 A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Throughout this application, reference will be made to objects that are created or instantiated by computer software. Such objects will have a data portion associated therewith for storing information, and have methods or functionality associated therewith to provide desired functionality to a client accessing the object. Typically, the methods of the object will be directed in part to manipulating the object&#39;s data. Such an abstract object has an associated state that is the cumulative effect of methods operating on the data. It is this state that will be stored by the innovative object state repository as explained in this application. 
     As used herein, the term “objects,” refers to software objects pertaining to a binary object model and that have binary extensibility through wrapping. Furthermore, such objects are interface-based meaning that an object is only used or operated through specific “interfaces” as defined hereafter and an interface-based binary object model will entail objects having multiple interfaces. In this sense, an object is only known through its interfaces and there is no specific reference to an object in its entirety. 
     An object may be active or loaded meaning that it is a functional part of a software program or system. An object is said to be persisted when the data portion or properties are stored, though it is more accurate to refer to the state of an object as being persisted. At a later time, an object of the same class may be instantiated and restored to the same state as the original object using the previously persisted object state. 
     As used herein, the term “binary extensibility” or “wrapping” refers to creating new object classes based on existing object classes regardless of the software code used to implement the various interfaces that make up a particular existing class. The extension model will expect interface functionality to be accessible through a binary convention regardless of actual source code used to arrive at the executable code. A “wrapped” object may use all or only some of the interface functionality implemented in a built-upon class, and some of the behavior of the built-upon class may be passed through to the clients of the wrapped object without the wrapped object knowing the nature of or even the existence of the behavior to be passed through. 
     One implementation of a binary object model and system that follows the characteristics of objects used throughout this application and as described above is the Component Object Model or COM as provided by Microsoft® Corporation as part of their Object Linking and Embedding (OLE) and ActiveX™ software technology. Reference to COM objects will be made as part of a specific and exemplary embodiment of the present invention. The invention, however, would fit any object model having the relevant characteristics of COM, namely, being an interface-based, binary object model supporting binary extensibility. 
     As used herein, the term “interface” refers to a specification for a particular and related subgroup of behavior and properties. Behavior or methods are typically a set of software subroutines, with each subroutine having a signature made up of the passed subroutine arguments, their order, and their data type. Further, each interface will have data associated therewith in the form of properties that are only accessible through a subroutine of the interface. Finally, an object may support multiple interfaces to thereby allow an object&#39;s characteristics to be defined by the interfaces that it supports and allow many classes to share behavior by supporting some of the same interfaces. 
     An interface, as part of the binary object system, also specifies a binary convention for accessing the software subroutines that support or implement the interface. Knowing the binary convention, the subroutine signatures that are defined by the interface, and a functional specification of how the subroutines are to behave, an object implementing a particular interface may be created using virtually any source code. Each such independently created object would be wholly unique and may represent internal data in a variety of different structures but from a binary standpoint would appear the same to an invoking client. Likewise, once an interface has been implemented and reduced to its binary form, any client may access the methods through the binary convention. 
     As used herein, the term “class” refers to a definition for directing a CPU to create an instance of an object. A class, therefore, will implement the interfaces that make up a given object and therefore is a template for creating objects. A class may be a source code definition that is compiled into executable code that will create run-time storage for the properties of an object and executable code to support the interface methods. 
     As used herein, the term “property” refers to a piece of data associated with an object. Further, the property may only be accessed through the appropriate interface method (e.g., subroutine). For example, for purposes of the presently preferred embodiment a “get” property subroutine and “put” property subroutine are implemented for retrieving and storing values for a particular property, respectively. 
     As used herein, the term “collection” refers to a special variant for a kind of property. More specifically, it is a set-valued property meaning that multiple items are formed into a collection. An item includes, but is not limited to, scalar values, such as integers, strings, etc., or may be an object (e.g., a handle to an interface of an object). Each collection will support methods for adding or removing an item as well as finding a particular item within the set and returning a count of how many items are in a set. 
     Throughout this application, when dealing with specific classes, a “C” will precede the class name so as to identify the name as that of a class. In like manner, an “I” will precede an interface name so as to identify name as that of an interface. For example, an object representing a square and having an interface to allow drawing of the square would be created by the CSquare class and would implement an interface IDraw that would include a method draw or draw( ). 
     FIG. 1A is a logical diagram showing the relationship between classes and interfaces. A plurality of interfaces exist as specifications for operating on an object, accessing particular properties as explained previously, and accessing the object&#39;s other behavior, such as methods. Interface  52  supports a number of methods and has a number of properties, while interface  54  also supports a number of methods (different than those of interface  52 ) and a number of properties (again, different from those of interface  52 ). Interfaces are defined as necessary by designers of particular software programs to encapsulate a related set of functionality. 
     Class  56  is a template for creating objects having interface  52 . Likewise, class  58  is a template for creating objects that have both interface  52  and interface  54 . Thus we can see that a particular interface may be defined by completely different templates or actual pieces of software code. For example, class  56  may be written in C++ while class  58  may be written in some other programming language. However, when objects are created by class  56  or class  58 , respectively, any program knowing the appropriate binary convention associated with the supported interfaces and the operation of the supported interfaces will be able to manipulate the object thus created as desired or to wrap and extend the object. 
     FIG. 1B is a logical diagram showing how a particular client may operate upon the instantiated objects (represented in clouds) through the specified interfaces. Object  60 , created from class  56 , supports interface  52 . Client  62  accesses or operates upon object  60  through interface  52  by invoking the methods according to the binary convention. A client may be an application program, another object, or any other software entity. Object  64 , created by class  58 , supports both interface  52  and interface  54  giving client  62  access to the respective methods and properties through either or both interfaces. Finally, object  66  is another instance of class  56  and supports interface  52 . Because each instantiation has its own data space, object  60  and object  66 , though created from the same class  56  and supporting the same interface  52 , will have different object states depending on how client  62  accesses and operates on the respective object through the interfaces. 
     It is important to recognize that an object, according to the present invention, is known to a client by its interfaces. Typically, on the tangible level, an interface will be accessed by a pointer, handle or other identifier that can be used by the client to eventually access the executable software through the binary convention established as part of the binary object system. 
     One example of the binary object system that is interface-based as explained above is the COM system by Microsoft. Each object according to the COM system must support a particular interface by definition. This interface, IUnknown, has a QueryInterface method that allows a client to inquire whether other interfaces are supported by the object by passing a globally unique identifier (GUID), called the interface identifier, that uniquely identifies the interface. If so supported, a pointer or reference to the interface is returned and the client may then access the functionality through COM&#39;s binary convention. Thus, IUnknown is an indicating interface that will lead to other interfaces supported by an object. 
     Object functionality may grow by adding new interfaces to an object that more advanced clients can access without harming the operation of older clients who are unaware of the new interfaces through the indicating interface IUnknown. 
     The binary convention in the COM object system for accessing the interface method is a reference to an interface&#39;s data area wherein the interface property values are stored in an implementation-specific format not normally known by the client. The first value of that data area, by definition, is another reference or pointer to a table of pointers known as a VTable. Each entry in the VTable is a pointer to a loaded executable code function that makes up one of the interface methods. In this manner, a client, given an interface pointer and a description of the interface may quickly find the correct subroutine to execute as desired. More details as to the details and way that COM is able to achieve binary extensibility and the binary linkage at the interface level may be found in COM specification documents. 
     For purposes of this disclosure and patent application, any general object-based system having such binary extensibility capabilities and being interface-based as explained previously will suffice as an underlying object system for implementing the present invention. A working knowledge of COM and OLE is presumed for purposes of understanding the implementation details of the currently preferred embodiment as explained hereafter. The COM/OLE technology is widely accepted in the computer industry and those skilled in the art will recognize application of the present invention to other similar object systems. 
     FIG. 2 is a logical diagram showing the class and interface relationship of an address book example that will be used throughout this application to illustrate the operation of the present invention. An address book will contain entries of information called contacts to represent persons. Each contact will contain information for a person&#39;s name, phone number, and e-mail address. 
     Two classes are defined for creating two different types of objects in order to logically implement the address book example as shown in FIG.  2 . First is the CAddressBook class  70  that implements the IAddressBook interface  72  while the other is the CContact class  74  that implements the IContact interface  76 . 
     Furthermore, there is a contains relationship  78  between the IAddressBook interface  72  and the IContact interface  76 . The arrows  80  and  82 , respectively, indicate that the IAddressBook interface  72  is the origin interface while the IContact interface  76  is the destination interface by definition. The contains relationship  78  itself, however, is a bidirectional link between the two interfaces and either interface is equally available to the other interface by navigating the contains relationship  78 . The origin and destination designations affect the storage layout of relationship instances and the semantics of certain operations on relationships. A source object is where a navigational session begins and the target object is the resulting object that is reached by navigating the relationship. 
     The implementation of a relationship between objects as defined between specific interfaces that may be contained in a respective object is the subject matter of the present invention. Different embodiments will be shown that illustrate different ways that this can be achieved according to the present invention. 
     The IAddressBook interface  72  contains as data the title property  84  as well as a contacts collection  86 . The values for the title property  84  and the contacts collection  86  are only available through methods defined on the IAddressBook interface  72 . More specifically, the GetTitle  88  and the PutTitle  90  methods will retrieve or place a value into the title property  84 , and the GetContacts method  92  will retrieve a contacts collection. 
     Collections have four different methods for manipulating the data therein: the Add and Remove methods will respectively place or delete an element into or from a collection; the Item method will retrieve a specific element from the collection; and the Count method will return the number of elements contained in the collection. Those skilled in the art will note that a collection may be implemented in a variety of different ways as will be shown hereafter in more detail. For example, a separate collection object may be used or a particular object may support an interface that defines collection functionality. 
     The contact collection  86  and address book collection  106  are used to implement the contains relationship  78  as will be shown in more detail hereafter. Furthermore, different embodiments will be shown for implementing the contains relationship  78 . 
     In like manner, the IContact interface  76  has a name property  100 , a phone property  102 , and an e-mail property  104  in addition to an address book collection  106 . In order to manipulate the properties and address book collection the following methods exist: GetName method  118 ; PutName method  116 ; GetPhone method  114 ; PutPhone method  112 ; GetEmail method  110 ; PutEmail method  108 ; and GetAddressBooks method  120 . These methods all operate in like manner as explained previously with the methods of the IAddressBook interface  72  to manipulate the data values of the name property  100 , phone property  102 , and e-mail property  104 , respectively, and the address book collection  106 . 
     FIG. 3 is a drawing of actual data values to be used with objects for the address book example structurally illustrated in FIG.  2  and shows the interrelationships between address books and contacts. Shown in FIG. 3 is address book  128  with the title of “Friends” containing four individual contacts. Address book  130 , on the other hand, is entitled “Attorneys” and contains only two contacts. A group of five contacts  132  is shown each having unique values for the respective properties including the address books that contain the contact. Each contact has a name property, a phone property, and an E-mail property. It may be noted that contact  134  is included in both address book  128  and address book  130 . 
     Referring now to FIG. 4, the relationships between the objects that make up the address book example illustrated by the logical diagram shown in FIG.  2  and using the data as shown in FIG. 3 is readily seen. Address book objects  136  and  138  will have relationships to the contact objects logically “contained” therein. In like manner, contact objects  140 ,  142 ,  144 ,  146  and  148  will have a relationship with the respective address books that they are “contained by.” 
     Since the relationship is bidirectional, the lines making the links between the objects have arrows on both ends as shown in FIG.  4 . The relationship between address book object  136  (“Friends” address book) and contact object  140  is represented by line  150 . Likewise the relationships between address book object  136  and contact objects  142 ,  144 , and  146 , respectively, are represented by lines  152 ,  154 , and  156 , respectively. For address book object  138  (“Attorneys” address book), the relationship with contact object  144  and contact object  148 , respectively, is represented by lines  158  and  160 , respectively. Note that contact object  144  (“Suzanne”) is related to both address book object  136  and address book object  138  as represented by lines  154  and  158 , respectively. 
     A relationship according to the present invention is a logical link between two interfaces on two objects rather than between the two objects directly. Typically, each interface will support collections of either related objects or of relationship objects that will lead to the related objects. Each of two related objects will be listed in the object collection of the corresponding related object. Furthermore, since the relationship is based on an interface supported by an object rather than a class used to create the object, different kinds of objects may be easily related as long as the related interface is supported. 
     Referring now to FIGS. 5A and 5B, definitional terminology and navigational terminology will now be developed. FIG. 5A shows object A  162  having a relationship to object B  164 . Relationships are defined on interfaces that are supported by an object and one interface will be designated the origin, by definition, while the other related interface will be designated the destination, again by definition. As shown in FIG. 5A, object A  162  supports the origin interface while object B  164  supports the destination interface with the relationship being defined directionally from the origin to the destination as shown by directional arrow  166 . The definitional designation as origin or destination for a particular interface is used logically by the designer of the system and for internal tracking of the relationships, however, the actual relationship between the objects is bidirectional and either of the related objects is available from the other by navigating the relationship. 
     In designating navigation, the beginning point object containing one of the related interfaces is designated the source object while the end point of the navigation is the target object containing the other related interface. Therefore, object A  162  may be the source object or the target object, depending on the direction of the navigation as shown by directional arrows  168  and  170 . Likewise, object B  164  may also be either the target object or the source object depending on navigational direction again as shown by respective directional arrows  168  and  170 . 
     Referring now to FIG. 5B, the relationship as defined in the logical diagram of FIG. 2 for the address book example is shown along with the data of FIG.  3 . By definition, the origin interface is the IAddressBook interface while the destination interface is the IContact interface. As shown in FIG. 5B, the lAddressBook interface is supported by the address book object entitled “Friends” and the address book object entitled “Attorneys” (address books objects  136  and  138 , respectively, as shown in FIG. 4) as shown enclosed by box  172 . Likewise, the destination interface is IContact with five objects having the name properties “Mindy,” “Amy,” “Suzanne,” “Toby,” and “Dave” (corresponding to contact objects  140 ,  142 ,  144 ,  146 , and  148 , respectively, of FIG. 4) as shown enclosed by box  174 . The “Contains” relationship defined between the interfaces is shown by the directional arrow  176 . 
     The box  178  with the plurality of directional arrows  180  into box  182  illustrates how each of the address book objects can be the source object in navigation towards each of the related target objects enclosed by box  182 . This shows all of the possible source-to-target object navigational possibilities from the address book objects to the contact objects of the address book example shown graphically in FIG.  4 . 
     Box  184  shows the same address book objects as being target objects from a navigation originating from the source objects enclosed in box  186  following the plurality of arrows  188  into the target objects. Again, all the possibilities for the contact object being the source and an address book object being the target for the address book example using the data of FIG. 3 are shown. Again, each of these relationships are shown graphically in FIG.  4 . 
     Referring now to FIG. 6A, one embodiment showing the interface defined logical link is shown. Object A  190  supports interface A that is related to interface B. As part of interface A on object A  190 , is a collection  192  of related objects. A collection of objects is a set-valued property that supports methods for adding an object, deleting an object, returning an object referenced by index count or ID, and for returning how many objects (target objects) are in the collection. Besides any other objects related to object A  190 , there will be a reference in collection  192  to object B  194  represented by directional arrow  196 . 
     Object B  194  will support an interface related to interface A, namely interface B. Furthermore, as part of interface B there will be a collection  198  of objects related to object B  194 . In order to make the link between the related objects complete, collection  198  will contain a reference to object A  190  having the related interface A. 
     FIG. 6A represents the link or relationship between objects each supporting the related interfaces in its simplest fashion. The collections  192  and  198  are fully supported by the respective object  190  or  194 . In other words, the method implementation, storage allocation, and other implementation details are completely handled by the classes that are used to instantiate or support objects corresponding to object A  190  or object B  194 . The relationship between the objects having the two types of related interface is completed once the entries for the respective related target object are entered into the respective collections found on the corresponding source objects. 
     In a currently preferred implementation using COM objects, the reference to another object is by way of an interface on that object. It is likely that the interface reference will be the related interface though any interface on that object may be used. The IUnknown interface that can be used as an indicating interface to arrive at other interfaces supported by an object when passed the GUID used to identify the particular interface may also be used according to the system design. 
     Referring now to FIG. 6B, the objects of FIG. 4 representing the address book example are shown as they would be related using the embodiment of FIG.  6 A. This graphical representation shows that a navigation will occur straight from a source object to a target object in a direct fashion. 
     Referring now to FIG. 7A, another embodiment of the present invention is shown wherein the collections of related objects are implemented in separate collection objects. In this embodiment, the collection object will provide the collection methods and be responsible for allocating storage of the references to objects contained in the collection. By implementing the collection as a separate object, the code implementing the collection may be written one time with different instances of the class being used by the various related interfaces and objects implementing those interfaces thereby reducing duplicative programming. 
     In the embodiment of FIG. 7A, object A  202  supporting interface A that is related to interface B has reference to a collection object  204  that contains therein a reference to object B  206 . Gaining access to the collection object  204  from object A  202  is represented by directional arrow  208 . Implemented on interface A will be a method to gain access to the collection object  204  thereby allowing the client to manipulate the object as necessary to complete the navigation to the desired target object. The reference from within the collection object  204  to object B  206  is represented by directional arrow  210 . 
     In similar fashion, the link between object A  202  and object B  206  is completed through listing on collection object  212  a reference to object A  202 . Again, access to collection object  212  from object B  206  is represented by directional arrow  214  and the reference to object A  202  found within collection object  212  is represented by directional arrow  216 . 
     A client navigating between object A  202  and object B  206  will use an object A  202  method to have access to collection object  204  and will use a method of collection object  204  in order to gain access to object B  206  and therefore complete the navigation from source object A  202  to target object B  206 . 
     Navigation in the opposite direction will occur by starting at source object B  206 , using a member method on object B  206  to arrive at collection object  212  and using an appropriate member method of collection object  212  to arrive at the target object A  202 . By implementing the collection of related objects as separate objects themselves, custom behavior may be implemented to such objects using the native object system wrapping or extensibility mechanisms. This allows further customization and reusability of code. 
     Referring now to FIG. 7B, the objects representing the address book example as shown in FIG. 4 are related according to the embodiment illustrated in FIG. 7A. A certain amount of efficiency is lost by using separate collection objects, however, greater flexibility is given to the system designer since no specific code to implement a collection need be written and wrapping or other extensibility mechanisms may be used to imbue the collection object with greater functionality. 
     Referring now to FIG. 8A, another embodiment of the present invention is shown wherein the collections are of specific relationship objects rather than the related objects themselves. The intermediate relationship object represents the actual relationship between two objects having the related interfaces and may have specific kinds of relationship behavior attributed thereto that provides greater functionality to the database clients using the relationship structure. Furthermore, customization may occur to a relationship object using the extensibility mechanisms associated with an object system so that the relationship behavior may be further customized. 
     As shown in FIG. 8A, object A  218  supports an interface A that is related to interface B. Furthermore, object B  220  having the related interface B is to be related to object A  218 . Interface A of object A  218  will have access to collection object  222  through a method of object A as represented by directional arrow  224 . The collection object  222  will have a reference to relationship object  226  as represented by directional arrow  228 . Access is gained to the relationship object  226  through a member function found on collection object  222 . 
     The relationship object  226  will contain the origin and destination references to each of object A  218  and object B  220  according to the relationship definition. Furthermore, relationship object  226  will have its own methods thereby giving it its own behavior to implement relationship functionality as necessary. For example, a method may be found thereon for getting the target object of a relationship. Naturally, the target object of the relationship will depend on the source object or the direction into which one arrives at the relationship object. For example, if the source object is object A  218  and the relationship object  226  has been accessed through collection object  222 , then the target object would be object B  220 . Again, the reference from the relationship object  226  to the object B  220  is represented by directional arrow  230 . In contrast, if the source object is object B  220 , then the relationship object  226  will provide a reference to the appropriate target object A  218 . 
     For the relationship to be fully defined between object A  218  and object B  220 , the collection object  232  associated with interface B found on object B  220  must have contained in the collection implemented thereon a reference to the relationship object  226  as represented by directional arrow  234 . Again, access to collection object  232  will be through a method found on the object B  220  as represented by directional arrow  236 . The relationship object  226  will, through its methods, give access to the object A  218  as represented by directional arrow  238 . 
     The navigational path between object A  218  to object B  220  will be from object A  218  to collection object  222  that contains a collection of all relationship objects representing relationships between object A and various related objects. One such relationship object is chosen as part of the navigation. For example, relationship object  226  may be chosen which, in turn, will be able to give references to the two objects that are related. From there, the related target object, object B  220  may be accessed using the appropriate method. 
     Referring now to FIG. 8B, the objects representing the address book example as shown in FIG. 4 have the relationships implemented using the embodiment shown in FIG.  8 A. While such a configuration increases the navigation overhead by placing an additional relationship object in the navigational path between related objects, specific forms of functionality may be implemented in the relationship object to give a more robust functionality to a system depending on the application. For example, validation methods may be implemented to assure that during the creation of a particular relationship that certain rules are followed. 
     Referring now to FIG. 9A, another embodiment of the present invention is illustrated where two collection objects are used to represent two different kinds of collections. One is used as a collection of related objects while the other is used as a collection of relationship objects used to arrive at the related object. In essence, such an arrangement simply combines the configuration shown for the embodiment illustrated in FIG.  7 A and the embodiment illustrated in FIG.  8 A. 
     Object A  240  having an interface A that is related to an interface B contained on object B  242  is related first through collection object  244  having a collection of related objects. This collection object  244  is accessed by a method of object A  240  as represented by directional arrow  246 . Finally, the related object, object B  242 , is accessed from collection object  244  through a method as shown by directional arrow  248  representing the reference to object B  242 . 
     Conversely, object B  242  has a collection object  250  associated therewith and accessed by a method as represented by directional arrow  252 , the collection object  250  getting access to object A  240  through a method as shown by directional arrow  254  representing the reference to object A  240 . This is in the same manner as explained previously in connection with the discussion for the embodiment shown in FIG.  7 A. 
     Additionally, FIG. 9A shows another navigational pathway between related objects, object A  240  and object B  242 . Object A  240  may have access to collection object  256  by means of a member function as represented by directional arrow  258 . Collection  256  contains references to relationship objects representing each and every relationship that object A  240  may have a relationship with. As shown, the collection object  256  has reference to relationship object  260  through a method contained thereon as represented by directional arrow  262  representing the reference to relationship object  260 . From the relationship object  260  access may be made to either object A  240  as shown by directional arrow  263  representing a reference to object A  240  or to object B  242  as shown through directional arrow  264  representing a reference to object B  242 . If navigation begins at object A  240 , a method of collection object  260  will be used to gain access to the object B  242 . 
     Conversely, object B  242  will have associated therewith collection object  266  that can be accessed by a method as shown by directional arrow  268  representing access to the collection object  266 . In order for the link between object A  240  and object B  242  to be complete, collection object  266  must have a reference to relationship object  260 . Relationship object  260  will be accessed through a method found on collection object  266  as represented by directional arrow  270  representing reference to the relationship object  260 . Again, from the relationship object  260  object A  240  may be accessed using methods and this is shown by the directional arrow  262  representing reference to object A  240 . 
     Using the intermediate relationship object  260  operates in the same manner as shown previously in connection with FIG.  8 A. By combining the two different embodiments as shown in FIGS. 7A and 8A, clients navigating between object A  240  and object B  242  (in either direction) have two different pathways from which to choose to perform the navigation. By going through the simpler pathway of a collection of related objects using the single collection object implementation as illustrated in detail in FIG.  7 A and explained previously, quicker access is achieved. By using the intermediate relationship object with the extra overhead of making another object access and associated processing as illustrated in detail in FIG.  8 A and explained previously, more robust functionality and greater capabilities are achieved. By implementing the object relationship as shown in FIG. 9A, the best of both worlds are presented to a client and a client may navigate the relationships in the most appropriate manner. 
     Those skilled in the art will note that providing access to the respective collection objects from related object A  240  or object B  242  can be achieved in different ways. For example, different methods of the same interface managing the contacts or address books collection will yield access to the object collection object or the relationship collection object. 
     FIG. 9B shows the interrelationship between the objects of FIG. 4 representing the address book example with the relationships implemented according to the embodiment shown in FIG.  9 A. By duplicating the relationship between the related objects using the direct collection method and the intermediate relationship object method, a client may choose the method of navigation based on client requirements. 
     Referring now to FIG. 10A, another embodiment of the present invention is used to create the relationship between object A  272  and object B  274 . This embodiment utilizes a single hybrid collection object that may return a reference to the target object or a reference to a relationship object that in turn will be used to access the target object. This is similar to the embodiment of FIG. 9A except that rather than implement the separate collections on separate collection objects, a single hybrid collection object will implement both collections. In this manner, a client will access a single collection object and utilize the methods on that object for using the collections to access a related object or a relationship object that leads to the related object. Some implementation may use some form of automatic accessing to use a single method that returns access to a relationship object or the related object according to some rule thereby relieving the client designer from the programming tedium of distinguishing between collections. 
     As shown in FIG. 10A, object A  272  will have associated therewith a hybrid collection object  276  that may be accessed through a method as illustrated by the directional arrow  278  representing access to collection object  276 . The hybrid collection object  276  manages two collections, namely, one collection of references to related objects and another collection of references to relationship objects defining a relationship between two objects. Methods of the hybrid collection object  276  will allow direct access to a related target object such as object B  274  as shown by the directional arrow  278  representing the reference to object B  274 . Additionally, the hybrid collection object  276  will have methods allowing access to relationship object  280  as shown by directional arrow  282  representing the reference to relationship object  280 . From the relationship object  280 , access may be had to either object making up the relationship. The access to related target object B  274  is shown by directional arrow  284  representing reference to object B  274 . 
     In order for the relationship link between object A  272  and object B  274  to be complete, the hybrid collection object  288  associated with object B  274  must have references to relationship object  280  and object A  272 . Access to hybrid collection object  288  from object B  274  is through a method and is represented by directional arrow  291  representing such access. Furthermore, from hybrid collection object  288 , access may be had to relationship object  280  by a method as shown by arrow  290  representing such access and access may be had to object A  272  through another method as shown by directional arrow  292  representing that access. From the relationship object  280 , access is made to object A  272  by a method as represented by directional arrow  286 . 
     Referring now to FIG. 10B, the objects associated with the address book example as shown in FIG. 4 with their several relationships implemented using the embodiment of the present invention as shown in FIG. 10A is shown. By having a single hybrid collection object that manages two different collections, clients navigating between the objects can utilize a more uniform path for arriving at a single object implementing both collections. 
     Another embodiment that is consistent with the object diagram in FIG. 10A places objects in the hybrid collection object as either the related object itself (for direct access) or a relationship object, but not both. This contrasts with the approach explained previously that places both the related object and the relationship object in the hybrid collection object. This embodiment may find particular relevance when relating objects of different types that may dictate different treatment. For example, the relationships emanating from an object that have relationship-specific behavior could be represented as relationship objects while those that do not have behavior could be represented directly as the destination object. Thus, according to this alternative embodiment, some of the items in a hybrid collection object would be relationship objects (assuming multiple related objects) while others would be the related objects themselves. In particular, either relationship object  280  or object B  274  would be in the hybrid collection object  276 , but not both. 
     All embodiments thus illustrated have a number of common factors according to the present invention although their implementation details are different. In each case, it is interfaces that define the relationship between objects. In other words, any objects including the two related interfaces may therefore be related by virtue of inclusion of those particular interfaces. In this manner, objects of different types and characters may be equally related in an object system where the objects may support multiple interfaces. This is in contrast to forming relationships between objects based on class definition of the object as is common practice. 
     In some object systems capable of supporting multiple interfaces, such as COM, a preferred object system for implementing the present invention, objects themselves are not directly accessible except through their interfaces. Therefore, in COM, a method that returns access to an object in its truest sense returns access to an interface into such object. 
     Additionally, though two interfaces of different types are defined to have a relationship between them, this “definition” means that each of those interfaces supports a collection that leads, either directly or indirectly, to those objects actually supporting the related interface. It is important to note that this collection may be empty therefore meaning that though an object may exist, no relationship exists to another object. The actual relationships can be made, removed, or modified during the lifetime of the object as appropriate. Furthermore, changes to collections associated with one object of a relationship must usually be accompanied by corresponding changes in collections associated with the other object of the relationship. For example, to delete a relationship, the link must be removed in both directions by removing references to related objects in both pertinent collections, each found on the related objects of the to-be-deleted relationship. 
     The object relationships according to the present invention and described in the various embodiments may be created by a computer program product directing and controlling a general purpose computer. The computer program product will consist of some medium such as magnetic disks or CD-ROM having computer readable program code means to configure the computer. The program code means will configure or cause the computer to make the relationships as described including all of the objects themselves. Furthermore, the program code means implementing the present invention will interact with existing program code means and additional program code means as a client to fully implement the configuration of the general purpose computer. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrated and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.