ENTITY RELATION MODEL

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: