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Degrees of Data Abstaction

الكلية كلية تكنولوجيا المعلومات     القسم قسم شبكات المعلومات     المرحلة 2
أستاذ المادة انوار جعفر موسى جعفر       31/10/2012 07:38:59
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 data base 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 data base is more difficult when each business unit works with only a subset of data.
- It makes applications program development much simpler.
- It is independent of both software and hardware. software independence means that the model does not depend on the DBMS software used to implement the model hardware independence means that the model does not depend on the hardware used in the implementation of the model-therefore, changes in either the hardware or the DBMS software will have no effect on the db designer at the conceptual level.
Logical design is used to refer to the task of creating conceptual data model


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