Context Diagrams Overview or Level 0

1
Context Diagrams (Overview or Level 0)

• Represent the system at a high level of detail.
• Comprised of
• One single process box for the entire system.
• External entities.
• The data flows that pass between the external
  entities and the system.

2
Context Diagrams (contd)

• Purpose
• to identify and examine the interfaces between
  the external entities and the system.

3
Example Context Diagram
Customer
order
Simple Order System
delivery_details
invoice
Customer
4
Level 1 Diagrams

• Show
• the system in more detail
• how data enters the system
• how these data items are transformed by the
  processes
• how they leave the system
• A Level 1 diagram must have the same number of
  inputs and outputs as its context diagram.
• The flows are connected to and from the actual
  processes which create, receive or change them.
• Processes are numbered 1, 2, 3 etc on a Level 1
  diagram.

5
Guidelines for Drawing a Context Diagram

• Read the case study a number of times.
• Try to list potential external entities.
• Establish what flows are sent to the system from
  the external entities.
• Establish what flows are sent from the system to
  the external entities.
• Draw the Context diagram.

6
Guidelines for Drawing a Level 1 Diagram

• Taking one sentence at a time try to identify
  potential processes (look for verbs).
• Identify and list the data flows.
• Identify and list the data stores.
• Draw the Level one diagram (using the correct
  notation).

7
Connectivity Validation

• Make sure the Level 1 diagram is fully connected.
• That is, a process must receive inputs from other
  processes or from data stores to be triggered.
• Check the Level 1 diagram against the context
  diagram for consistency
• flows across the boundaries must be the same
• names must be the same