Aggregation and Composition in Object - Relational Database Design

Recently, there have emerged more sophisticated applications, which have to represent complex objects related with complex relationships, such as aggregations and compositions. New object-relational databases are more appropriated than relational databases to support complex objects. Besides, the most common way of designing databases is using the E/R model, without taking in account the program design. However, new object-oriented design techniques, such as UML (Universal Modelling Language), permit modelling the full system, including the database schema, in a uniform way. Besides, as UML is an extensible language, it allows introducing new stereotypes for specific applications if it is needed. So, new stereotypes for database design can be also defined. The framework of this paper is an Object-Relational Database Design Methodology. The methodology specifies new UML stereotypes for Object-Relational Database Design as well as it proposes some guidelines to translate an UML schema into an object-relational one. The guidelines are based on the SQL:1999 object-relational model and in Oracle8i as an example of product. In this paper we focus on the design of two UML constructors: aggregation and composition. We propose its implementation in Oracle8i, because unlike SQL:1999, Oracle8i supports a data type, the nested table, that is specially appropriated to represent the UML aggregation and composition.