ISMT221 Information Systems Analysis and Design

1. ISMT221Information Systems Analysis and Design Entity-Relationship Diagram Lab 4 Tony Tam

2. Agenda • Presentation • About Entity-Relationship Diagram • Explaining the ERD • Build up some fundamental information • Your turn • Setup environment for ERD • Draw a very simple ERD • Practice on narrative text ERD drawing

3. Entity-Relationship Diagram • Conceptual data model of the data (data store) • Logical data model • Independent of the physical data model • i.e. I can use different physical database (e.g. Oracle, SQL Server, Sybase) with the same conceptual data model • Works together with DFD to give a full picture of the whole system

4. Entity-Relationship Diagramming • Crow’s Foot Notation • Relationship with Foot • Cardinality • Minimum cardinality • Minimum number of instances (0) • Maximum cardinality • Maximum number of instances (many) Maximum is MANY Minimum is ZERO

5. Explaining ERD • PK – primary key • FK# - foreign key (reference key) • Bolded attributes – Mandatory field • The relationship read as: • 0:M Student belongs to 1:1 major • 1:1 Major is composed of 0:M Student Must be active verb Must be singular

6. What are they? • Candidate Key • All available unique, required identifiers of an entity • Primary Key • A unique, required identifier of an entity • The best one of candidate keys • Foreign Key • A reference key to another entity • This key is the primary key of another entity