Entity Relationship Modelling (ER Model)
Saturday, December 11, 2010|
adminIn an effective system, data is divided into discrete categories or entities. An Entity Relationship (ER) Model is an illustration of various entities in a business and the relationships between them. An ER model is derived from business specifications or narratives and built during the analysis phase of the system development life cycle.
ER models separate the information required by a business from the activities performed within a business. Although businesses can change their activities, the type of information tends to remain constant. Therefore, the data structures also tend to be constant.
Benefits of ER Modeling
- Documents information for the organization in a clear, precise format
- Provides a clear picture of the scope of the information requirement
- Provides an easily understood pictorial map for the database design
- Offers an effective framework for integrating multiple applications
Key Components ER Modeling
- Entity: A thing of significance about which information needs to be known. Examples are departments, employees, and orders.
- Attribute: Something that describes or qualifies an entity. For example, for the employee entity, the attributes would be the employee number, name, job title, hire date, department number, and so on. Each of the attributes is either required or optional. This state is called optionality.
- Relationship: A named association between entities showing optionality and degree. Examples are employees and departments, and orders and items.
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Database Management Systems
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