Entity-Relationship Diagramming

Abstract

Database design is fundamentally a task in data modelling. A data model is an architecture for data (chapter 10). Brodie has made a distinction between three generations of data model (Brodie, 1984): 1. Primitive Data Models. In this approach objects are represented by record-structures grouped in file-structures. The main operations available are read and write operations over records. 2. Classic Data Models. These are the hierarchical, network and relational data models. The hierarchical data model is an extension of the primitive data model discussed above. The network is an extension of the hierarchical approach. The relational data model is a fundamental departure from the hierarchical and network approaches. 3. Semantic Data Models. The main problem with classic data models like the relational data model is that they maintain a fundamental record-orientation. In other words, the meaning of the information in the database, its semantics, is not readily apparent from the database itself. The user of databases using the classic approach must consciously apply semantic information. For this reason, a number of so-called semantic data models have been proposed (King and McLeod, 1985). Semantic data models (SDMs) attempt to provide a more expressive means of representing the meaning of information than is available in the classic models.