Category: DBMS

Explanation about Key Constraint in ER Model

Consider the Works_In relationship shown in the following figure. An employee can work in several departments, and a department can have several employees, as illustrated in the Works_In instance as shown in the following figure. Employee 231-31-5368 has worked in Department 51 since 3/3/93 and in Department 56 since 2/2/92. Department 51 has two employees. …

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Entity Relationship Model

The entity-relationship (ER) data model allows us to describe the data involved in a real-world enterprise in terms of objects and their relationships and is widely used to develop an initial database design. The ER model is important primarily for it’s role in database design. It provides useful concepts that allow us to move from …

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