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

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

Learning Outcomes Problem with ER Models Specialization / generalization Aggregation Composition

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)

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

Entity Definition Types Diagram Notation An object or concept 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

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

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)

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)

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

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