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Entity-Relationship (E-R) Model

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Presentation on theme: "Entity-Relationship (E-R) Model"— Presentation transcript:

1 Entity-Relationship (E-R) Model
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 Types Diagram Notation An object or concept
Strong entity (parent, owner, dominant) Weak entity (child, dependent, or subordinate) Diagram Notation Rectangular

6 Attribute Domain Types Single Composite Single-valued Multi-valued

7 Key Candidate key Primary key Composite key

8 Relationship Definition Diagram Notation Degree of a relationship
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 EER model example
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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