Degrees of data Abstraction
If you ask ten data base 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 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
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
|