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Entity relationship diagram Name: Quian Crosby Form:6AQ Subject: Information Technology Teacher: Ms. D. Anderson.

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Presentation on theme: "Entity relationship diagram Name: Quian Crosby Form:6AQ Subject: Information Technology Teacher: Ms. D. Anderson."— Presentation transcript:

1 Entity relationship diagram Name: Quian Crosby Form:6AQ Subject: Information Technology Teacher: Ms. D. Anderson

2 What is an Entity Relationship Diagram? An entity-relationship (ER) diagram is a specialized graphic that illustrates the interrelationships between entities in a database.

3 What are the symbols used in ERD? There are three basic elements in ER models: Entities are the "things" about which we seek information. Attributes are the data we collect about the entities. Relationships provide the structure needed to draw information from multiple entities.

4 What is a one-one relationship? One-to-one relationships occur when there is exactly one record in the first table that corresponds to exactly one record in the related table.

5 What is a one-many relationship? One-to-many relationships occur when each record in Table A may have many linked records in Table B but each record in Table B may have only one corresponding record in Table A.

6 What is a many-many relationship?. In a "many to many“ relationship, one record in either table can relate to many records in the other table


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