Chapter 11 & 12 Entity-Relationship (E-R) Model 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 Design tools and documentation for data base structure No physical DBMS Proposed by Dr. Peter Chen

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

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

Attribute Domain Types –Single –Composite –Single-valued –Multi-valued –Derived

Key Candidate key Primary key Composite key Alternative key

Relationship Definition –Association among entities Diagram Notation –Line – (role name) Degree of a relationship –number of participating entities –types Unary (recursive relationship) Binary Ternary Quaternary

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 –Chasm trap

Enhanced Entity-Relationship Model Additional entity types –Superclass (generalization) –Subclass (specialization) Constraints –Participation (mandatory, optional) –Disjoint: disjoint (or), non-disjoint (and) Attribute Inheritance –Specialization hierarchy –Generalization hierarchy Other –Aggregation (has a or is part of) –Composition (strong ownership of aggregation)

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

Assignment Review chapters 9-12 Read chapter 13 Homework assignment –11.11 (enhanced e-r diagram) –Due date: