2.1: Databases and the Three-Schema Architecture
This article presents the three-schema architecture, which aims to provide data independence. The three schemas are external, conceptual, and internal. Each provides a level of independence: application independence from the external schema, external schema independence from the conceptual schema, conceptual schema independence from the internal schema, and internal schema independence and thus application independence from the physical data itself.
Read chapters 3 and 4. In chapter 3, the three ANSI/SPARC schemas are presented as phases of database development: the requirements phase, the high-level design phase, the detailed design phase, and the implementation phase. These correspond to the external model, the internal model, and the physical model, respectively. This chapter also describes entity-relationship modeling as a means of representing a conceptual model. Chapter 4 discusses conceptual modeling for hierarchical, network, and relational databases.