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Database

Database. Dr. Roueida Mohammed. The Entity Relationship Model. The entity relationship model (or ER model) is a way of graphically representing the logical relationships of entities (or objects) in order to create a database. Elements of the E/R Model. Entity sets . Attributes .

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Database

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  1. Database Dr. Roueida Mohammed

  2. The Entity Relationship Model • The entity relationship model (or ER model) is a way of graphically representing the logical relationships of entities (or objects) in order to create a database.

  3. Elements of the E/R Model • Entity sets. • Attributes. • Relationships

  4. Entity-Relationship Diagrams • An E/R diagram is a graph representing entity sets, attributes, and relationships. Elements of each of these kinds are represented by nodes of the graph, and we use a special shape of node to indicate the kind, as follows: • Entity sets are represented by rectangles. • Attributes are represented by ovals. • Relationships are represented by diamonds

  5. RELATIONSHIP SETS • one-to-one • one-to-many • many-to-one • Many-to-many

  6. Design Principles • Faithfulness • Avoiding Redundancy • Simplicity Counts • Choosing the Right Relationships • Picking the Right Kind of Element

  7. The Modeling of Constraints • Keys • Single-value constraints • Referential integrity constraints • Domain constraints • General constraints

  8. Weak Entities

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