Data Modelling
Completion requirements
Read this chapter and learn the models listed in order of decreasing level of abstraction. Pay attention to the summary given on conceptual models. Complete the exercises at the end of the chapter.
Schemas
A schema is an overall description of a database, and it is usually represented by the entity relationship diagram (ERD). There are many subschemas that represent external models and thus display external views of the data. Below is a list of items to consider during the design process of a database.
- External schemas: there are multiple
- Multiple subschemas: these display multiple external views of the data
- Conceptual schema: there is only one. This schema includes data items, relationships and constraints, all represented in an ERD.
- Physical schema: there is only one