Defining the Term

Defining the Term "Object/Relational"

Object/relational is one term that is used to describe database management systems that provide extensible data types to manage non-traditional data. IBM describes the term object/relational to encompass not just large objects, but also support for triggers, user-defined distinct types, and user-defined functions. These three topics are covered in Chapters 4, "Using DB2 User -Defined Functions and Data Types" and 8, "Using DB2 Triggers for Integrity." This chapter covers DB2's implementation of large objects.

Do not be confused by the use of the term "object" in the phrase "object/relational." An object/relational database management system has little to do with object-oriented technology or object-oriented programming and development.

NOTE

OO technology is fundamentally based upon the concept of, what else, but an object. Objects are defined based on object classes that determine the structure ( variables ) and behavior ( methods ) for the object. True objects, in traditional OO parlance, cannot be easily represented using a relational database. In the RDBMS, a logical entity is transformed into a physical representation of that entity solely in terms of its data characteristics. In DB2, you create a table that can store the data elements (in an underlying VSAM data file represented by a table space). The table contains rows that represent the current state of that entity. The table does not store all of the encapsulated logic necessary to act upon that data. By contrast, an object would define an entity in terms of both its state and its behavior. In other words, an object encapsulates both the data (state) and the valid procedures that can be performed upon the object's data (behavior). With stored procedures, triggers, and UDFs relational databases are "getting closer" to supporting OO techniques, but the implementation is significantly different.

Another term used in the industry when referring to extensible data type support is "universal." IBM went so far as to rename and brand DB2 as DB2 Universal Database for OS/390 as of Version 6 ”and it is still named DB2 Universal Database (or UDB) as of V8. Large object support is the primary factor governing the applicability of the term "universal" to DB2.