Data Model
Is a relatively simple representation, usually graphical, of more abstraction of a more complex real- world object event, a data model represents data structures and their characteristics , relations , constraints , transformations , and , other constructs with purpose of supporting a specific problem domain .
The Importance of Data Models
Data models can facilitate interaction among the designer, the applications programmer, and the end user, a well- developed data model can even foster improved understanding of the organization for which the database design is developed.
Data Model Basic Building Blokes
Entity: is anything (a person, a please, a thing, or an event) about which data are to be collected and stored. An entity represents a particular type of object in the real world entities are "distinguishable" that is each entity occurrence is unique and distinct. For example, a CUSTOMER entity would have many distinguishable customer occurrences such as Ahmed, Ali, etc.
Attribute: is a characteristic of an entity. For example, a CUSTOMER entity would bed described by a attributes such as customer last name, customer first name, its equivalent of fids in the file systems
Relationship: describes an association among entities for example a relationship exists between customers and agents that can be described as follows: an agent can serve many customers, and each customer may be served by one agent.
Data models use three types of relationships
- one-to-many(1:M or 1..*)relationships
A painter paints many different paintings, but each one of them is
painted by only one painter
- Many-to-many (M: N or *..*) relationship
An employee may learn many job skills many be learned by many
- one-to-one(1:1or 1..1) relationship
A retail company s management structure may require that each of
its stores be managed by a single employee. In turn, each store
manager, who is an employee, managed only a single store.
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 .
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