15. Physical Database Considerations
There are three very distinct and important rules or tenets about databases that are critical to keep in mind. These are separation/insulation of the program and data, multiple user access activity support, and usage of a repository to store the database schema. The purpose of the three-level architecture is to separate the user from the physical database. As one can see from Figure 15.1, the three levels consist of the following:
1. An internal level or schema, which describes the physical storage requirements and structure of the database. This will describe the complete details of the data storage requirements in terms of files and space needed for data stores, as well as indexing ...