Database systems are the key to implementing information modeling. Information modeling in databases can be carried out at two different levels: conceptual data modeling and logical database modeling. Correspondingly, we have conceptual data models and logical database models for information modeling. Generally the conceptual data models are used for information modeling at a high level of abstraction and at the level of data manipulation, i.e., a low level of abstraction, the logical database model is used for information modeling. Database modeling generally starts from the conceptual data models and then the developed conceptual data models are mapped into the logical database models.

The logical database models will be discussed in Chapter 2. In this chapter, we focus on the conceptual data models. We will briefly introduce the entity-relationship (ER) model, the enhanced (extended) entity-relationship (EER) model, and the class model of the Unified Modeling Language (UML). In addition, with the popularity of Web-based applications, the requirement has been put on the exchange and share of data over the Web. The XML (eXtensiable Markup Language) provides a Web-friendly and well-understood syntax for the exchange of data and impacts on data definition and share on Web (Seligman and Rosenthal, 2001). So this chapter will briefly present the XML.