The Object Database Management Group Oracle Database Tips by Donald Burleson

The Object Management Group (OMG)

The balancing between the vendors drive toward being unique and the industries need to be standard has been addressed with the formation of the Object Management Group.  The Object Management Group (OMG) was formed in May of 1989 by Christopher Stone and eight companies to set standards for object technology. These companies included American Airlines, Canon, Data General, Hewlett-Packard, Philips Telecommunications, Sun Microsystems, Unisys Corporation, and 3Com Corporation. 

The OMG is committed to developing specifications that are vendor independent, commercially viable, and superior technically for object technology.   OMG promotes object technology as a way to allow interoperability and portability, increase productivity, and promote reusability. The OMG has expanded from the original eight companies to over 700 members, only corporate members may submit technology for the OMG to adopt. The OMG headquarters are located in Framingham, Massachusetts.

The main objective of the OMG is interoperability and portability of object technology.  This is being driven by end-users who want "plug and play" software, software for both today and tomorrow must be flexible and open so that end-users can change the way their systems are developed and used.

In 1991, the OMG first introduced the Common Object Request Broker Architecture (CORBA) specification.  CORBA is concerned with interoperability so that different hardware and software products can communicate with each other.  Unfortunately, se still see some pushback from the large software vendors about CORBA.  Microsoft has been notably absent in the development of the CORBA standard, and has developed their own approach to system interoperability with DCOM which is used with Object Linking and Embedding (OLE).  While DCOM has been designed to be "largely CORBA compliant", it still has vendor-specific features that are unique to Microsoft.

The Object Database Management Group

The haphazard development of standards and definitions of object technology has been very confounding to most companies who are interested in using the new technology.  Object technology companies cannot agree on the definition of an object-oriented database, much less the characteristics of an object-oriented database.  Many vendor products which are advertised as object-oriented capitalize on object technology buzzwords and are often very vague about the real features of the database, and what makes it object-oriented.  This is especially true for some of the new object/relational database offerings.

The "pure" object-oriented databases, such as Versant and Objectivity/DB are very powerful tools, but they are tightly-coupled to a programming language.  Because of their complexity and the high learning curve for using the engines these types of object-oriented databases have had trouble achieving popularity in the general marketplace. 

A new standard for object-oriented database architecture called the ODMG Object Model has been proposed by a consortium of vendors, but the mega-vendors such as IBM and Microsoft have not accepted this standard.

ODMG is a vendor organization which is dedicated to providing standards exclusively for object-oriented databases.  The ODMG object model was developed jointly be a consortium of object-oriented database vendors.  These companies feel a sense of urgency in creating a unified standard for object-oriented databases, and they have prepared the ODMG model in the hope that all OODB vendors will adopt the model.  Current commercial OODB systems are not portable across hardware platforms, and it is hoped that a joint approach toward object-oriented database architecture will create an environment where object-oriented systems share many characteristics, just as relational databases share common interfaces, such as SQL.

Because of a lack of standards for object-oriented database architectures, most of the major OODB vendors have been creating commercial products which have very diverse internal structures.

The ODMG object model was developed jointly by a consortium of object-oriented database vendors, including Versant, Ontos, O2 technology, Object Design, SunSoft, and Objectivity corporations.  Notably absent was Microsoft Incorporated, who may have decided that their approach to Object databases technology did not fit into the industry standard plan.  These companies felt a sense of urgency in creating a unified standard for object-oriented databases, and they have prepared the ODMG model in the hope that all OODB vendors will adopt the model.  But beware, the ODMG database standard was never meant for the object/relational databases such as UniSQL, Oracle, and Informix.  These vendors have had no real standard to guide their efforts. 

The ODMG model creates an independent model which is language independent, and object models may be bound to many different languages.  ODMG develops a hierarchy of objects with the most general object called a "denotable" object.  Denotable objects may be either mutable or immutable.  A mutable object may changes its values and properties, but an immutable object contains only literal values.

Within immutable objects, we find two sub-categories, atomic and structured. (Figure 4.3) A denotable, immutable, atomic object is represented by the same data types found in a relational database, namely CHAR, INTEGER, and FLOAT.  A denotable, immutable, structured object is a literal structure such as the DATE and TIME data types.

Figure 4.4 - The ODMG-93 Database Standard

Unlike the relational database model, the ODMG model requires that all object are assigned an object identifier (OID), to uniquely identify the object.  While it is unclear, it appears that it is not possible to reference an object by the data values in the object.  For example, in a relational database one could state: SELECT * FROM ORDER WHERE ORDER_NBR = 456; this would not be possible under this object model.  Rather, the ODMG model requires "database currency" to locate the object, and the system must know the OID.

As things stand, the ODMG93 specification remains in the exclusive domain of the pure object-oriented database vendors.  Since the world's leading database vendors have chosen to ignore the ODMG specification in their efforts to objectize their relational engines, it remains to be seem whether the ODMG standard will ever achieve the status of a true industry standard.

Summary

While the emergence of standard for database objects has been making some headway, it is still clear that there is a great deal of work that must be done before all objects will be able to communicate with each other in an independent fashion.  As long as vendors have an incentive to keep their products proprietary, we will continue to see resistance in the marketplace, and a failure to develop a uniform method for interoperability within the database object community.

Now that we have explored the realm of standards, let's move on to take a look at how the object model is being implemented by some of the major database vendors.  The following chapters will explore the new object extensions to the database model and describe how these extensions are used to develop robust object-oriented applications.

 

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