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Chapter 11 & 12

Chapter 11 & 12. Entity-Relationship (E-R) Model. Agenda. Characteristics of E-R Model Components of E-R Model Example of E-R Model Enhanced E-R Model. Characteristics of E-R Model. Semantic data model Express the logical properties of an enterprise database

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Chapter 11 & 12

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  1. Chapter 11 & 12 Entity-Relationship (E-R) Model

  2. Agenda • Characteristics of E-R Model • Components of E-R Model • Example of E-R Model • Enhanced E-R Model

  3. Characteristics of E-R Model • Semantic data model • Express the logical properties of an enterprise database • Design tools and documentation for data base structure • No physical DBMS • Proposed by Dr. Peter Chen • Unified Modeling Language (UML)

  4. Components of E-R Model • Entity • Attribute • Key • Relationship • Structural constraints on relationship

  5. Entity • Definition • An object or concept • Types • Strong entity (parent, owner, dominant) • Weak entity (child, dependent, or subordinate) • Diagram Notation • Rectangular

  6. Attribute • Domain • Types • Single • Composite • Single-valued • Multi-valued • Derived

  7. Key • Candidate key • Primary key • Composite key

  8. Relationship • Definition • Association among entities • Diagram Notation • Line – (relation or role name) • Degree of a relationship • Number of participating entities • Types • Unary (recursive relationship) • Binary • Ternary • Quaternary

  9. Structural Constraints on Relationship • Cardinality constraints • Zero-to-one 0..1 • Zero-to-many 0..* • One-to-many 1..* • Many-to-many *..* • Participation constraints • Total (mandatory, every one involved) • Partial (optional, only some involved) • Improper relationship • Fan trap (ambiguous pathway) • Chasm trap (missing pathway)

  10. Enhanced Entity-Relationship Model • Additional entity types • Superclass: including one or more distinct subgroups in the data model • Subclass: a distinct subgroup of an entity type in the data model • Attribute Inheritance • Specialization hierarchy (specialization: maximizing the differences between members of an entity by identifying their distinguishing characteristics) • Generalization hierarchy (generalization: minimizing the differences between entities by identifying their common characteristics) • Is-A hierarchy • Constraints on specialization/generalization • Participation (mandatory, optional) • Disjoint: disjoint (or), non-disjoint (and) • Other • Aggregation (has a or is part of) • Composition (strong ownership of aggregation)

  11. Design Steps • Identify • Entity types, relationship types • Cardinality and participation constraints • Attributes • Keys • Specialize/generalize • EER diagram • EER model example

  12. Create an enhanced ER diagram for a rental management using following entities: • Rental agency • Staff • Part time • Full time • Owner • Renter • Property • Business • Home

  13. Points To Remember • Characteristics of E-R Model • Components of E-R Model • Example of E-R Model • Enhanced E-R Model

  14. Assignment • Review chapters 5, 6, 9, 10, 11, and 12 • Read chapter 13 • Homework assignment • 11.11 (enhanced e-r diagram) • Due date: • Exam 2 date:

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