LECTURES 2 + - 3 :

INFORMAL SPECIFICATION METHODS

A. Data Flow Diagrams (DFDs)

• Functional Descriptions : output = f(input)

• Graphical Notation : Functions, IO, Data Flow, Data Storage

• Examples : Arithmetic Expressions, Air Traffic Monitoring,

             Library System

• Issues :

            Ambiguity

            Control : Conditionals, and/or , Triggers

            Objects, Structures, and Relations

 

 

B. Entity Relationship (ER) Diagrams

• Descriptions of Data Structures and Relations

• Basic ER Elements : Entities, Relations, Attributes

• Example : World Traveller

• Issues : Completeness, Constraints on Relations