Chapter XIX Object - Relational Modeling

IntroductIon Modeling techniques play an important role in the development of database applications. Well-known entity-relationship modeling and its extensions have become a widely-accepted approach for relational database conceptual design. An object-oriented approach has brought a new view of conceptual modeling. A class as a fundamental concept of the object-oriented approach encapsulates both data and behavior, whereas traditional relational databases are able to store only data. In the early 1990s, the difference between the relational and object-oriented (OO) technologies, which were, and are still used together to build complex software systems, was labeled the object-relational impedance mismatch (Ambler, 2003). The object-oriented approach and the need of new application areas to store complex data have greatly influenced database technology since that time. Besides appearance of object-oriented database systems, which fully implement object-oriented paradigm in a database environment (Catell et al., 2003), traditional relational database management systems become object-relational, introduced object-relational features to the standard and leading database producers have already released packages which incorporate them. Development of complex data intensive software systems involves a close working relationship between software and database developers. Currently, software developers deal with object-Object-Relational Modeling oriented software development and use object-oriented modeling techniques to represent the main view of the application, whereas database developers model, design, build, and optimize the database. However, modeling techniques for relational databases do not support important features of object-relational databases. In addition, shared vision and clear communication of project details are necessary conditions for a software project to be successful. A common modeling language and supporting development tools can provide good conditions for it. The Unified Modeling Language (UML) was adopted as an OMG (Object Management Group) standard for object modeling in 1997. Since that time, it has become popular and widely used. It provides several modeling techniques (diagrams) that visualize a system from different perspectives. From database design point of view, a class diagram is the most important diagram—it shows a set of structural elements and their static relationships. It can be used for conceptual modeling of persistent classes. But the UML does not contain direct support neither for capturing important features of relational databases, nor for specific features of object-relational databases that are necessary for modeling data stored in a relational database and objects stored in an object-relational database at design levels below the conceptual one. Therefore, it is necessary to add the ability to model features of this kind of …