Database Modeling in UML.docVIP

Database Modeling in UML Introduction When it comes to providing reliable, flexible and efficient object persistence for software systems, todays designers and architects are faced with many choices. From the technological perspective, the choice is usually between pure Object-Oriented, Object-Relational hybrids, pure Relational and custom solutions based on open or proprietary file formats (eg. XML, OLE structured storage). From the vendor aspect Oracle, IBM, Microsoft, POET and others offer similar but often-incompatible solutions.This article is about only one of those choices, that is the layering of an object-oriented class model on top of a purely relational database. This is not to imply this is the only, best or simplest solution, but pragmatically it is one of the most common, and one that has the potential for the most misuse.We will begin with a quick tour of the two design domains we are trying to bridge: firstly the object-oriented class model as represented in the UML, and secondly the relational database model. For each domain we look only at the main features that will affect our task. We will then look at the techniques and issues involved in mapping from the class model to the database model, including object persistence, object behavior, relationships between objects and object identity. We will conclude with a review of the UML Data Profile (as proposed by Rational Software).Some familiarity with object-oriented design, UML and relational database modeling is assumed. The Class Model in the UML is the main artifact produced to represent the logical structure of a software system. It captures the both the data requirements and the behavior of objects within the model domain. The techniques for discovering and elaborating that model are outside the scope of this article, so we will assume the existence of a well designed class model that requires mapping onto a relational database. The Class ModelThe class is the basic logical entity