1. Entity Relationship Modeling
Chapter 11 & 12
Entity Relationship Modeling
(ER)
Thomas Connolly, Carolyn Begg, Database System, A Practical Approach to Design Implementation and Management, 4th Edition, Addison Wesley
Pg 342~ 386

2. Learning Outcomes Entity types Relationship types Attributes
Strong and weak entity type
Attributes on relationship
Structural constraints

3. Learning Outcomes Problem with ER Models
Specialization / generalization
Aggregation
Composition

4. 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)

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

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

7. Attribute Domain Types Single Composite Single-valued Multi-valued
Derived

8. Key
Candidate key
Primary key
Composite key

9. 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

10. 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)

11. 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)

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

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