ITEC 3010 - L6: Traditional Approach to Requirements

Traditional Approach vs. OOA

Two approaches to system modeling: Traditional focuses on processes and data; OO focuses on interacting objects.

Data Flow Diagrams (DFDs)

A graphical model that shows all main requirements for an information system in one diagram.

DFD Symbols

The symbols used in DFDs: square (external agent), rectangle (process), arrows (data flows), flat rectangle (data store).

Context Diagrams

The highest-level DFD summarizing all processing activity for the system, showing system boundaries and data flows.

DFD Fragments

Created for each use case in the event table, focusing on a single event within a single process symbol.

Levels of Abstraction

DFDs can be decomposed into higher-level and lower-level diagrams, providing multiple views of the system.

Physical DFDs

Describes the assumptions about implementation technology, developed in later stages of analysis.

Logical DFDs

Assumes implementation in perfect technology, does not describe how the system is implemented.

Evaluating DFD Quality

Factors include readability, consistency, accurate representation of requirements, and minimizing complexity.

Black Hole

Occurs when a process has data input but no output, violating flow rules; all inputs must have corresponding outputs.

Miracle

Occurs when a process produces output with no input; it represents unrealistic data flow.

Documenting DFD Components

Each process, data flow, and data store must be described, focusing on contents and data elements.

Structured English

A method of writing process specifications combining programming techniques with narrative English.

Decision Tables

A tabular method for summarizing complex decision logic, making descriptions more readable.

Decision Trees

A visual method for representing decision logic, providing a clear structure for complex conditions.

Data Flow Definition

A textual description of the content and internal structure of data flows, listing elements.

Data Element Definitions

Descriptions of data types and representations, including validation rules and length specifications.

Data Store Definitions

A data store on a DFD represents a data entity on the ERD; definitions are provided for unlinked stores.

Components of Traditional Analysis Model

The four components: DFDs, ERD, process definitions, and data definitions form an interlocking set of specifications.