UML Sequence Diagrams

During the requirements analysis phase, the system can be treated as a single "black box", which means that we can look at the system's behavior (what it does) without explaining how it does it. Read this section to see an example of a simplified trace diagram that shows only system input events. This is called a system sequence diagram.

14. How to Create a Contract

Apply the following advice from Liu, to create a contract for a system operation 

1. Identify the system operations from the system sequence diagram. 

2. For each system operation, construct a contract. 

3. Start by writing the Responsibilities section, informally describing the purpose of the operation. 

4. Then complete the Post-conditions section, declaratively describing the state changes that occur to objects in the conceptual model. 

5. To describe the post-conditions, use the following categories:

  • Instances creation and deletion. 
  • Attributes modification. 
  • Associations formed and broken.