8 - Object-Relational Design

Abstract

This chapter focuses on the interplay of object orientation and databases. Programming languages in which application software is written play a large role in this interplay, and are discussed. This also leads naturally into a discussion of how to store XML data in a relational database. This chapter begins with an overview describing object orientation. The following two sections continue with a discussion of object-oriented and object-relational databases. Object orientation is a standard feature of many modern programming languages and software systems. Central features of object-oriented systems include inheritance, identity, encapsulation, and abstraction. Typical database systems are relational and not object-oriented. This results in an “impedance mismatch” as data is moved between tables in a relational database and objects in the application program. Object-oriented database systems have been proposed as a means for addressing this mismatch by having the database system explicitly designed to support objects with links. Rather than build an object-oriented database, one could also attempt to manage better the mismatch between object-oriented systems and relational databases. Toward this end, relational database systems have added some object management capabilities, including support for large objects, user-defined functions, and abstract data types. In parallel with these efforts, there are also many tools that simplify and automate the task of storing object data in a relational database.