Lecture 3

Degrees of Data Abstraction

If you ask ten database designers what is a data model, you will end up with ten different answers. Depending on the degree of data abstraction.
In 1970s the American National standards Institute (ANSI) defined a framework for data modeling based on degrees of data abstraction.

The External Model

It is the end users view of the data environment the term end users refers to people who use the application programs to manipulate the data and generate information.
Because data is being modeled, ER diagrams will be used to represent the external views. A specific representation of an external view is known as external schema.
The use of external views representing subsets of the database has sum important advantages:

- It makes it easy to identify specific data required to support each business units operations.
- It makes the designer s job easy by providing feedback about the models adequacy. Specifically the model can be checked to insure that it supports all processes as defined by their external models, as well as all operational requirements and constraints.
- It helps to ensure security constraints in the data base design. Damaging an entire database is more difficult when each business unit works with only a subset of data.
- It makes applications program development much simpler.