er_diag - Entity-Relationship Model[ER Model OUTLINE ER...

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Entity-Relationship Model [ER Model]
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OUTLINE box4 ER Model Concepts square6 Entities and Attributes square6 Entity Types, Value Sets, and Key Attributes square6 Relationships and Relationship Types square6 Weak Entity Types square6 Roles and Attributes in Relationship Types box4 ER Diagrams - Notation box4 ER Diagram for COMPANY Schema
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ER MODEL box4 Entity-Relational model is a popular high level conceptual data model and is used for conceptual design of database applications box4 E-R facilitate database design by representing overall logical structure of a database by specifying the properties of the data. box4 E-R data model employs three basic notions : square6 Entity sets square6 Relationship square6 Attributes box4 The E-R model is usually expressed as an E-R diagram
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Entities and Attributes box4 An entity is a thing or an object in the miniworld that are represented in databases. square6 Entity has set of properties and values . square6 Eg: Employee, Department, Person. box4 Attributes: Properties used to describe the entity. square6 EMPLOYEE Entity has four attributes Name, Address, Age, Phone. box4 Each entity has a value for each of its attributes . square6 Eg: Name=‘JONES’, Address=‘Harrington Road’,Age=40,Phone=01- 44-3470727
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Entity and Attributes Two entities Employee and Company and their attributes
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Types of Attributes box4 Attributes can be square6 composite / simple (atomic) square6 single-valued / multivalued square6 stored / derived square6 key / nonkey.
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Types of Attributes box4 Simple : Attribute that has a single atomic value or not divisible. square6 Example: SSN. box4 Composite : The attribute that can be divided into smaller subparts.
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