Method and apparatus for automatic generation of object oriented code for mapping relational data to objects

Claims

What is claimed is:

1. A method for automatically mapping information of an object said information comprising the object attributes, relationships, and inheritances between an object-oriented application and a structured database, said method being carried out using a digital computing system comprising a processor, said method comprising the steps of:

executing instructions on said processor to load into temporary storage an object model, said object model comprising a plurality of semantic elements, said semantic elements being less complex than object class source code definitions, representing a plurality of object classes and a plurality of relationships between said plurality of object classes within said object-oriented application, each of said plurality of semantic elements comprising relationships between object classes, inheritances between object classes, and attributes of an object class comprising at least one object ID attribute;

executing instructions on said processor to automatically generate code by parsing said object model to identify the object classes and their relationships for which said code is generated and automatically generating class definitions and methods, said code being suitable for conversion to an executable form that when executed automatically maps said information between said object-oriented application and said structured database; and

executing instructions on said processor to output to persistent storage said code.

2. A method for automatically mapping information of an object comprising the object attributes, relationships, and inheritances between an object-oriented application and a structured database, said method being carried out using a digital computing system comprising a processor, said method comprising the steps of:

executing instructions on said processor to load into temporary storage an object model, said object model comprising a plurality of semantic elements, said semantic elements being less complex than object class source code definitions, representing a plurality of object classes and a plurality of relationships between said plurality of object classes within said object-oriented application, each of said plurality of semantic elements comprising relationships between object classes, inheritances between object classes, and attributes of an object class comprising at least one object ID attribute;

executing instructions on said processor to load into temporary storage for processing a database schema that represents the structure of data in said structured database, said structured database comprising tables, columns, primary keys, foreign keys, and join tables;

executing instructions on said processor to load into temporary storage for processing a transform that represents a mapping between said object model and said database schema, said transform having the further capability of being modified;

executing instructions on said processor to automatically generate code by parsing said object model to identify the object classes and their relationships for which said code is generated, parsing said database schema to identify the database tables used to store the object class instances, and parsing said transform to identify the mapping of said object classes, and relationships between said database tables and said object classes, said code being suitable for conversion to an executable form that when executed automatically maps said information between said object-oriented application and said structured database;

executing instructions on said processor to generate code for each object class, including code for four routines associated with said object class, said four routines being:

a routine to create an instance of said object class;

a routine to retrieve an instance of said object class;

a routine to update an instance of said object class; and

a routine to delete an instance of said object class, each of said four routines based on said semantic elements of said object model; and

executing instructions on said processor to output to persistent storage said code.

3. The method of claim 2 wherein said step of executing instructions on said processor to load into temporary storage for processing a database schema comprises executing instructions on said processor to load into temporary storage from persistent storage said database schema, and wherein said step of executing instructions on said processor to load into temporary storage for processing a transform comprises executing instructions on said processor to load into temporary storage from persistent storage said transform.

4. The method of claim 2 wherein said computing system further comprises an input means coupled to said processor, wherein said step of executing instructions on the processor to load into temporary storage for processing a database schema comprises executing instructions on said processor in conjunction with said input means to input said database schema, and wherein said step of executing instructions on said processor to load into temporary storage for processing a transform comprises executing instructions on said processor in conjunction with said input means to input said transform.

5. The method of claim 2 wherein said step of executing instructions on said processor to load into temporary storage for processing a database schema comprises executing instructions on said processor to construct said database schema by loading said object model into temporary storage, locating object classes and relationships within said object model, creating said database schema comprising semantic representations of tables representing said object classes and relationships of said object model such that said database schema represents a database capable of storing said elements of said object model, and wherein said step of executing instructions on said processor to load into temporary storage for processing a transform comprises executing instructions on said processor to construct said transform by loading said object model into temporary storage, locating object classes and relationships within said object model, creating said transform comprising mappings between said object classes and relationships of said object model and said tables of said database schema such that said transform is capable of mapping said elements of said object model from said object oriented application to said structured database.

6. The method of claim 2 wherein said step of executing instructions on said processor to load into temporary storage an object model comprises executing instructions on said processor to load into temporary storage an object model;

wherein said step of executing instructions on said processor to load into temporary storage for processing a database schema said database schema describing tables organized in rows and columns, each one of said tables having at least one primary key column that uniquely identifies rows in each said table; and

wherein said step of executing instructions on said processor to load into temporary storage for processing a transform includes executing instructions on said processor to load into temporary storage for processing a transform that comprises a set of mappings between said semantic elements of said object model and said database schema.

7. The method of claim 6 wherein said step of executing instructions on said processor to automatically generate code further comprises executing instructions on said processor to generate code which performs a mapping from each one of said object classes from said object model to at least one table described by said database schema, according to said mappings of said transform.

8. The method of claim 6 wherein said step of executing instructions on said processor to automatically generate code further comprises executing instructions on said processor to generate code which performs a mapping from said object ID attributes from said object model to primary key columns in at least one table described by said database schema, according to said mappings of said transform.

9. The method of claim 6 wherein said step of executing instructions on said processor to automatically generate code further comprises executing instructions on said processor to generate code which performs a mapping from attributes from said object model to columns in a single table described by said database schema, according to said mappings of said transform.

10. The method of claim 6 wherein said step of executing instructions on said processor to automatically generate code further comprises executing instructions on said processor to generate code for implementing a one-to-one relationship between object classes of said object model by generating code that references at least one foreign key column in at least one table described by said database schema, said foreign key column being capable of use in said create, retrieve, update, and delete routines for preserving said one-to-one relationship between said object classes, and said foreign key column being specified according to said mappings of said transform.

11. The method of claim 6 wherein said step of executing instructions on said processor to automatically generate code further comprises executing instructions on said processor to generate code implementing a one-to-many relationship between object classes of said object model by generating code that references at least one foreign key column in at least one table of said database schema, said foreign key column being capable of use in said create, retrieve, update, and delete routines for preserving said one-to-many relationship between said object classes, and said foreign key column being specified according to said mappings of said transform.

12. The method of claim 6 wherein said step of executing instructions on said processor to automatically generate code further comprises executing instructions on said processor to generate code implementing a many-to-many relationship between object classes of said object model in said structured database by generating code that references a join table described by said database schema, said join table containing foreign key references to primary key columns, said join table being capable of use in said create, retrieve, update, and delete routines for preserving said many-to-many relationship between said object classes, and said join table being specified according to said mappings of said transform.

13. The method of claim 6 wherein said step of executing instructions on said processor to automatically generate code further comprises executing instructions on said processor to generate code which implements the vertical inheritance between a child object class and a parent object class of said object model in said structured database by referencing at least one foreign key column in a table described by said database schema that corresponds to said child object class, representing said vertical inheritance according to said mappings of said transform.

14. The method of claim 6 wherein said step of executing instructions on said processor to automatically generate code further comprises executing instructions on said processor to automatically generate code which implements the horizontal inheritance between a child object class and a parent object class of said object model in said structured database by copying attributes of said parent object class from said object oriented application to a table described by said database schema corresponding to said child object class according to said mappings of said transform.

15. The method of claim 2 wherein said step of executing instructions on said processor to automatically generate code comprises executing instructions on said processor to automatically generate code for a plurality of object classes determined by said object model and a set of routines for each object class of said plurality, such that said routines operate on an instance in said object oriented application of said object class.

16. The method of claim 2 wherein said step of executing instructions on said processor to automatically generate code comprises executing instructions on said processor to automatically generate code for a plurality of object classes determined by said object model and a set of routines for each object class of said plurality, each said set comprising

a routine for creating an object instance of said object class, said routine for creating an object instance of said object class being suitable for conversion to an executable form that when executed causes a new object instance to be created in said object-oriented application and further causes the attributes of said new object instance to be added to columns of tables of said structured database according to said database schema and said mapping of said transform, and further causes relationships and inheritance of said object model to be implemented by modifying columns, tables and keys in said structured database according said mapping of said transform.

17. The method of claim 2 wherein said step of executing instructions on said processor to automatically generate code comprises executing instructions on said processor to automatically generate code for a plurality of object classes determined by said object model and a set of routines for each object class of said plurality, each said set comprising

a routine for retrieving an object instance of said object class from said structured database, said routine for retrieving an object instance being suitable for conversion to an executable form that when executed causes a new object instance to be created in said object-oriented application, said new object instance being initialized with attribute values, relationships, and inheritances determined according to information extracted from said structured database.

18. The method of claim 2 wherein said step of executing instructions on said processor to automatically generate code comprises executing instructions on said processor to automatically generate code for a plurality of object classes determined by said object model and a set of routines for each object class of said plurality, each said set comprising

a routine for updating an object instance of said object class, said routine for updating an object instance being suitable for conversion to an executable form that when executed causes modifications to the database tables, columns and keys representing the object instance in said structured database and further causes the attribute values, inheritances, and relationships of said object instance in said object-oriented application to be modified to reflect said modifications to said database tables, columns, and keys representing the object instance in said structured database.

19. The method of claim 2 wherein said step of executing instructions on said processor to automatically generate code comprises executing instructions on said processor to automatically generate code for a plurality of object classes determined by said object model and a set of routines for each object class of said plurality, each said set comprising

a routine for deleting an object instance of said object class, said routine for deleting an object instance being suitable for conversion to an executable form that when executed causes an object instance to be deleted in said object-oriented application and further causes the database tables, columns, primary keys, foreign keys, and join tables representing the object instance to be updated reflecting the deletion of the object instance from said object oriented application in said structured database.

20. The method of claim 2 wherein said step of executing instructions on said processor to automatically generate code comprises executing instructions on said processor to automatically generate a create routine for each object class in a plurality of object classes determined by said object model, said create routine comprising the step of generating an attribute of the object instance comprising the object ID by combining the attributes specified in said object model and transform as defining the object ID such that an object instance is uniquely identifiable within said structured database and said object oriented application.

21. The method of claim 19 wherein said step of automatically generating a delete routine for each object class in a plurality of object classes determined by said object model further comprises the step of canceling the deletion of an object instance in said structured database based on the existence of a blocking relationship between said object instance and a related object instance in said object model.

22. The method of claim 19 wherein said step of automatically generating a delete routine for each object class in a plurality of object classes determined by said object model further comprises the step of generating code to call a second delete routine for a related object instance based on the existence of a propagate relationship between said first object instance and said related object instance in said object model.

23. The method of claim 19 wherein said step of automatically generating a delete routine for each object class in a plurality of object classes determined by said object model further comprises the step of removing the columns, foreign keys, and join table entries in said structured database representing a remove relationship between a first object instance and a related object instance based on the existence of a remove relationship between said first object instance and said related object instance in said object model.

24. The method of claim 2 wherein said step of executing instructions on said processor to automatically generate code comprises executing instructions on said processor to automatically generate code for object classes and routines using as inputs said object model, said database schema, and said transform, at least one routine of said generated routines calling a notification hook routine in connection with the execution of said at least one routine of said generated routines, said notification hook routine being externally generated.

25. The method of claim 2 wherein said step of executing instructions on said processor to automatically generate code comprises executing instructions on said processor to automatically generate code for object classes and routines by loading into temporary storage from persistent storage said object model, said database schema, and said transform, including generating a source code routine to create at least one table in said structured database that corresponds to an object class in said object model.

26. A method for automatically mapping information between an object-oriented application and a plurality of structured databases, each of said structured databases comprising tables, columns, primary keys, foreign keys, and join tables, said method being carried out by executing instructions on a digital computing system comprising at least one processor, said method comprising the steps of:

executing instructions on a processor of said digital computing system to load into temporary storage an object model, said object model comprising a plurality of semantic elements, said semantic elements being less complex than object class source code definitions, representing a plurality of object classes and a plurality of relationships between said plurality of object classes within said object-oriented application, each of said plurality of semantic elements comprising relationships between object classes, inheritances between object classes, and attributes of an object class comprising at least one object ID attribute;

executing instructions on said processor to automatically generate code, said code being suitable for conversion to an executable form that when executed automatically maps said information between said object-oriented application and the structured databases of said plurality;

executing instructions on said processor to generate code for each object class, including code for four routines associated with said object class, said four routines being:

a routine to create an instance of said object class;

a routine to retrieve an instance of said object class;

a routine to update an instance of said object class; and

a routine to delete an instance of said object class, each of said four routines based on said semantic elements of said object model; and

executing instructions on said processor to output to persistent storage said code.

27. The method of claim 26 wherein said step of executing instructions on said processor to automatically generate code further comprises executing instructions on said processor to parse object classes from said object model and to generate code such that each one of said object classes maps to at least one table in at least one structured database of said plurality of structured databases.

28. A method for automatically generating code to support an object-oriented application that interacts transparently with a field-delimited database, said method performed by a processor coupled to an input means and an output means, said method comprising the steps of:

(a) executing instructions on said processor to enable a user to dynamically specify an object model to load into temporary storage by using said input means to select from a plurality of input fields representing said object model, said object model comprising a plurality of semantic elements, said semantic elements being less complex than object class source code definitions, representing a plurality of object classes and a plurality of relationships between said plurality of object classes within said object-oriented application, each of said plurality of semantic elements comprising relationships between object classes, inheritances between object classes, and attributes of an object class comprising at least one object ID attribute;

(b) executing instructions on said processor to load into temporary storage a database schema;

(c) executing instructions on said processor to load into temporary storage a transform, said transform representing a mapping between said object model and said schema;

(d) for each object class in said object model, executing instructions on said processor to generate code for each object class, including code for four routines associated with said object class, said four routines being:

a routine to create an instance of said object class;

a routine to retrieve an instance of said object class;

a routine to update an instance of said object class; and

a routine to delete an instance of said object class, each of said four routines based on said semantic elements of said object model; and

executing instructions on said processor and outputting to persistent storage the code thus generated.

29. An apparatus for automatically mapping information between an object-oriented application and a structured database, said apparatus comprising a digital computing system, said digital computing system comprising a first processor, a memory coupled to said processor, a user interface coupled to said processor, a storage device coupled to said processor, a network coupled to said processor, a second processor dedicated to a structured database coupled to said network and supporting said structured database, and:

means for executing instructions on said first processor to load into temporary storage an object model, said object model comprising a plurality of semantic elements, said semantic elements being less complex than object class source code definitions, representing a plurality of object classes and a plurality of relationships between said plurality of object classes within said object-oriented application, each of said plurality of semantic elements comprising relationships between object classes, inheritances between object classes, and attributes of an object class comprising at least one object ID attribute;

means for executing instructions on said processor to automatically generate code that when executed automatically maps said information between said object-oriented application and said structured database;

executing instructions on said processor to generate code for each object class, including code for four routines associated with said object class, said four routines being:

a routine to create an instance of said object class;

a routine to retrieve an instance of said object class;

a routine to update an instance of said object class; and

a routine to delete an instance of said object class, each of said four routines based on said semantic elements of said object model; and

means associated with said first processor for outputting said code to persistent storage.

30. The method of claim 6 wherein said step of executing instructions on said processor to load into temporary storage for processing a database schema further includes executing instructions on said processor to load into temporary storage for processing a database schema that describes tables organized in rows and columns, each one of said tables further containing a foreign key column that represents a mapping between a row in said table and a row in another table of said structured database.

COPYRIGHT NOTIFICATION

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owners have no objection to the facsimile reproduction, by anyone, of the patent document or the patent disclosure, as it appears in the patent and trademark office patent file or records, but otherwise reserve all copyright rights whatsoever.

MICROFICHE APPENDICES

Two appendices comprising a total of 1444 frames on 16 microfiche are included as part of this application. Appendix I contains the source code of Persistence.TM. version 1.3 released Jun. 15, 1993. It comprises 1358 frames on 14 microfiche. The Persistence.TM. software represents an embodiment of the method of the present invention. Appendix II contains a user's manual for Persistence.TM. version 1.2 released March 1993. It comprises 100 frames on 2 microfiche.

The source code in Appendix I represents unpublished work, Copyright.COPYRGT. 1993 Persistence Software, Inc. All rights reserved. The user's manual in Appendix II is Copyright.COPYRGT. 1993 Persistence Software, Inc. All rights reserved. For both Appendices I and II, copyright protection claimed includes all forms and matters of copyrightable material and information now allowed by statutory or judicial law or hereafter granted, including without limitation, material generated from the software programs which are displayed on the screen such as icons, screen display looks, etc.

BACKGROUND OF THE INVENTION

The invention relates to the interrelationship of databases, particularly relational databases, and object-oriented systems. More particularly, the invention relates to relationships between objects in object-oriented systems and descriptions of objects storable in field-delimited database structures. Field-delimited databases can structure data into fields which have common attributes. For example, relational databases can structure data into tables, each with columns and rows (in "n" dimensions) forming tuples, upon which certain operations in set algebra can be performed very conveniently.

Object-oriented applications organize data and routines together into encapsulated units referred to as objects. Object-oriented applications lead to modular software systems which have increased flexibility and are easy to alter and maintain.

An object model is a formal description of an object-oriented application. The semantic elements of an object model describe object classes, attributes of object classes, relationships between object classes, and inheritance between object classes. An object model provides a powerful mechanism to represent the real world, for example because objects carry information about inherited characteristics and relationships with other objects. For example, an object model of a car can contain many classes, such as "tire." The tire class can have attributes, such as "pressure"; relationships, such as "tire" is related to an "axle"; and inheritances, such as a "snow tire" inherits from a "tire."

The difference between a relational database management system (RDBMS) and an object-oriented application is that an object "knows" what operations can be performed on its data, whereas an RDBMS only has a set of generic operations which can be performed on its tuples. The semantics available in an object model are not preserved in a relational database. For example, a "snow tire" knows that it is related to an "axle" and inherits from a "tire." In contrast, a relational database represents this information in three separate data tables with no explicit representation of the relationships between the tables. The tire table in a relational database might have foreign key information referring to the axle table, but this representation of the relationship between tire and axle is implicit. It is up to the developer to know about these relationships, what they mean, and how to handle them.

There is a desire to build object-oriented applications that store and access data found in relational databases. For example, it would be useful to employ a plan for an automobile (an object model) to build a vehicle (an object) from an organized inventory of auto parts (a relational database). A system is needed which can map information between a database and an object-oriented application based on the semantics of an object model. More particularly, what is needed is a mechanism for using the semantic elements of an object model to generate routines that map data between a database and an object-oriented application.

Systems are known for manual mapping between objects in knowledge bases and database management systems. One approach is to employ a static class library as an interface between an object-oriented system and a relational database. An example is METHOD FOR INTEGRATING A KNOWLEDGE-BASED SYSTEM WITH AN ARBITRARY RELATIONAL DATABASE SYSTEM, U.S. Pat. No. 4,930,071 issued May 29, 1990 and assigned to IntelliCorp, Inc. of Mountain View, Calif. In static-type systems, objects can be extended to handle concepts such as relationships and inheritance, but they must be manually extended if they are to model complex real world structures. This limits their usefulness to building relatively simple object models from existing data, such as those used in rapidly building prototype systems. It is believed that there are commercial systems which use the static-type class approach. Among the candidates include "ProKappa" from IntelliCorp, "DB.H++" from Rogue Wave of Corvallis, Oreg., and possibly "Open ODB" from Hewlett Packard Company of Cupertino, Calif. and "UniSQL from UniSQL of Austin, Tex.

SUMMARY OF THE INVENTION

According to the invention, a method and apparatus are provided for using an object model of an object-oriented application to automatically map information between an object-oriented application and a structured database, such as a relational database. This is done by taking into account all of the semantics (implications) of an object model, such as inheritance and relationships among object classes, and using these semantics to generate a minimal set of routines for each object class that manipulate the object and other objects to which it is related or from which it inherits. The generated routines, when executed (that is, when converted to an executable form which is then executed), provide transparent access to relational data or other field-delimited data. Object classes and routines generated using the method encapsulate all the details of database access, such that developers (computer programmers) can write object-oriented applications using those object classes without any explicit reference to or knowledge of the underlying database or its structure. By working with the objects, the user of such applications transparently manipulates the database without needing to know anything of its structure. Applications can be written using the object classes to transparently integrate information from multiple databases.

The method of the invention comprises accepting a user-defined object model as a "blueprint" for an object-oriented application; accepting or constructing a schema of the structure of data in a database; and accepting or constructing a transform defining the mapping between the database schema and the object model. Based on these inputs the method automatically generates source code routines for each object class to perform four tasks: to create, retrieve, update, and delete instances of the object class and automatically make the corresponding changes in the database. These source code routines can subsequently be executed.

The invention will be better understood by reference to the following detailed description in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a computer system in accordance with the invention.

FIG. 2 is a schematic diagram representing the correspondence between a database schema and an object model by means of a transform.

FIG. 3 is a flow chart representing an overview of the method steps.

FIG. 4 is a flow chart representing the process for constructing the database schema and transform.

FIG. 5 is a flow chart representing the process for writing code which when executed creates an object instance and its corresponding structured information in the database.

FIG. 6 is a flow chart representing the process for writing code which when executed retrieves an object instance base on its corresponding structured information in the database.

FIG. 7 is a flow chart representing the process for writing code which when executed updates an object instance and its corresponding structured information in the database.

FIG. 8 is a flow chart representing the process for writing code which when executed deletes an object instance and makes corresponding changes to structured information in the database.

DESCRIPTION OF A SPECIFIC EMBODIMENT

Following is a description of a specific embodiment of the method of the present invention. Section 1 sets forth terminology that is used in the remainder of the description. Section 2 provides a description of a computing system that can be used to support the steps of the method. Section 3 describes the inputs to the method. Section 4 describes an overview of the method steps. Sections 5 and 6 give more detailed descriptions of specific method steps. Section 7 concludes the description.

1. Terminology

It is helpful to clarify the general meanings of terms used in connection with object-oriented systems.

An "object class" is a set of data (attributes) and functional capabilities (routines) encapsulated into a single logical entity. For example, an employee class may be characterized by a telephone number attribute and a "hire.sub.13 employee" routine.

An "object instance" is an embodiment (instantiation) of an object class. Instances are differentiated from one another by their attribute values, but not their routines (capabilities). For example, Jane Smith may be a first person-object instance and John Doe may be a second person-object instance. The term "object" is often used by itself to refer loosely to either an object class or an object instance, the difference being understood in context.

An "object-oriented application" is an operational computer program which when employed on an appropriate computer system uses a set of object instances that work in cooperation to perform useful work. For example, an object-oriented application could be built to manage personnel records for a company, including such operations as hire new employee or add an employee to a department.

An "object model" is a set of object classes that together form a blueprint for building an object-oriented application. Each object class of an object model can have attributes, inheritances, and relationships.

A "relationship" defines a link between two object classes. For example, an employee class may be related to the department class Each specific employee for example, "Jane Smith," would have a relationship with a specific department, such as "engineering." Relationships can be one-to-one, one-to-many, or many-to-many. An example of a one-to-one relationship can be a relationship between employee and parking place such that each employee can have a single parking place. An example of a one-to-many relationship can be a relationship between department and employee such that each department can employ multiple employees. An example of a many-to-many relationship can be a relationship between employee and project such that each employee serves on multiple projects, and each project consists of multiple employees.

"Attributes" are data elements of object classes which are expressed through particular values in object instances. For example, a person class can have the attribute "name", and a particular person instance can have the name value "Jane Smith."

An "object ID" is used to uniquely identify each object instance. The object ID can generated in one of two ways. It can be generated by the application, which can automatically assign a unique object ID for each new object instance. Alternatively it can comprise a set of attributes that are guaranteed in the object model to always form a unique set of values for an instance. In this case, the create routine will require a unique set of attributes in order to create a new object instance.

A "routine" is a functional capability associated with an object class. For example, the routine "hire.sub.13 employee" could be used to create a new employee instance.

"Inheritance" represents a specialization of an object class in which the specialized class shares all of the attributes and routines of parent classes. Thus the employee class can inherit certain attributes, such as name, from the person class. In this case, the person class is called the "parent" of the employee class, and the employee class is called the "child" of the person class.

Inheritance can extend across many object class "generations." For example, the object class "snow tire" can inherit from the object class "tire" which in turn can inherit from the object class "car.sub.-- part". In this example, "car.sub.-- part" is a parent of the object class "tire" and an ancestor of the object class "snow tire".

Inheritance can be "vertical" (concrete) or "horizontal" (abstract) according to how the information corresponding to inherited attributes is stored in the database. In the case of vertical inheritance between two object classes in an object model, the database contains data associated with each object class. In the case of horizontal inheritance between two object classes in the object model, the database does not contain data associated with each object class. For example, suppose that there are two object classes, "and that "employee" inherits "person" and "employee" inherits from "person." If this inheritance is vertical, then there can be a "person" table in the database which contains the attributes for each "person". If the inheritance is horizontal, there is no "person" table in the database. All the attributes of "person" are found in the "employee.sub.-- data" table. Horizontal and vertical inheritance can be mixed within the same object model.

The attributes, inheritances, and relationships of all the object classes of an object model are called the "semantics" or "semantic elements" of the object model. An object model contains certain information associated with its semantics. For each attribute, the object model contains information as to whether that attribute is to be associated with the object