Structuring System Requirements:

1

• Chapter 5
• Structuring System Requirements
• Process Modeling

5.1
2
ReviewSA Requirements Determination

• Data Collection
• Deliverables

3
Systems AnalysisStructuring Requirements

• Process modelshows how data flows in, out and
  between the system environment and its components
• Data-flow Diagrams (DFD)
• Graphically illustrate movement of data between
  external entities and the processes and data
  stores within a system

5.3
4
Process Modeling

• Deliverables and Outcomes
• Context data-flow diagram (DFD)
• Scope of system
• Level-0 Diagram
• Levels 1, 2, 3, etc. diagrams to increase
  specificity of system
• Project dictionary and CASE repository

5.4
5
Process Modeling (continued)

• Deliverables and Outcomes (continued)
• Project dictionary and CASE repository
• Data-flow Diagramming Mechanics
• Four symbols are used
• See Figure 5-2
• Developed by Gane and Sarson

5.5
6

• Data Flow
• Depicts data that are in motion and moving as a
  unit from one place to another in the system
• Drawn as an arrow
• Select a meaningful name to represent the data

5.6
7

• Data Store
• Depicts data at rest
• May represent data in
• File folder
• Computer-based file
• Notebook
• Drawn as a rectangle with the right vertical line
  missing
• Label includes name of the store as well as the
  number

5.7
8

• Process
• Depicts work or actions performed on data so that
  they are transformed, stored, or distributed
• Drawn as a rectangle with rounded corners
• Number of process as well as name are recorded

5.8
9

• Source/Sink
• Depicts the origin and/or destination of the data
• Sometimes referred to as an external entity
• Drawn as a square symbol
• Name states what the external agent is
• Because they are external, many characteristics
  are not of interest to us

5.9
10
Context Diagram

• Sets scope of an system that shows the system
  boundaries, external entities that interact with
  the system and the major information flows
  between the entities and the system

5.10
11
Level-0-Diagram

• Level-0 Diagram
• A data-flow diagram (DFD) that represents a
  systems major processes, data flows, and data
  stores at a higher level

12
Developing DFDs An Example

• Hoosier Burgers Automated Food Ordering System
• Context Diagram (Figure 5-4) contains no data
  stores

5.12
13
5.13
14
Hoosier BurgerDiagram 0

• Next step is to expand the context diagram to
  show the breakdown of processes (Figure 5-5)

5.14