1. Sequence Diagrams

2. Analysis Paralysis
“Do you want it perfect or do you want it now?”

3. Watch out for Red Herrings

4. Faulty Assumptions
In the second lecture we drew up the following detailed specification…
The consultant sits at their desk with a stack of business cards and flyers. They pick up a business card and start to input the details into system. The first field they enter is the name of the company. While doing this the system looks up the company name to see if it is already on the system. The next field the user enters is the name of the contact. Whilst dong this, the list of contacts for that company is displayed such that if the contact is already on the system the user may move onto another business card. At this point the user should have the opportunity to update the details on the system should they note that some aspect has change e.g. address.

5. From this we drew up an initial event table…
Subject
Verb
Object
Response
Consultant
Inputs
Card
Data accepted by the system
System
Checks
Identifying duplicates
Updates
New data input

6. Resulting in the following initial use case diagram…

7. There is a problem Back to that red herring
If we collected business cards like stamps then yes we would be interested in recording individual cards
What’s more important in our case isn’t the cards but the data they contain
We are interested in business intelligence on the companies and the people they employ
This new insight means we need to re-visit all the other associated documentation!

8. We Need to Revise the Specification
The consultant sits at their desk with a stack of business cards and flyers. They pick up a business card and start to input the details into system. The user is interested in recording details of the individual and associated company. The first field they enter is the name of the company. While doing this the system looks up the company name to see if it is already on the system. The next field the user enters is the name of the contact. Whilst dong this, the list of contacts for that company is displayed such that if the contact is already on the system the user may move onto another business card. At this point the user should have the opportunity to update the details on the system should they note that some aspect has change e.g. address.

9. And the Event Table Subject Verb Object Response Consultant Inputs
Company Name
System produces a list of companies with that name
System
Finds
Company
Produces a list of companies with that name
Lists
Employees
Produces a list of employees at each company
Adds
Company added to the system
Employee
Employee added to the system
Updates
Employee details updated
Company details updated

10. And the Use Case Diagram

11. And Probably the Class Diagram

12. The Sequence Diagram
Allows us to cross check our use cases and classes
The smoke and mirrors prototype informs this process
Need to think in terms of what classes support our use cases…

13. Triangulation Not a simple linear process
Class Designs
Use Cases
Sequence Diagram
Not a simple linear process
Things we discover later shed light on what we thought we knew previously

14. First go at the Sequence Diagram
Actors
Objects
Life lines
Messages

15. Important Questions to Ask
Do we have an actor on the use case that matches the sequence diagram?

16. Important Questions to Ask
Do we have a classes that map to those on the sequence diagram?

17. Important Questions to Ask
Do we have operations in the classes that are able to handle the messages?
FilterByCompanyName
FilterByCompanyNo

18. Revise the Class Diagram

19. So What Data Comes Back?
We may also find clues to the attributes (CompanyName / CompanyNo)

20. Extending the Sequence Diagram
Can we return list data from one life line to another?
Do we have an operation to support this message?

21. Revise the Class Diagram

22. What About Validation?

23. Modify the Use Case Diagram

24. Where to Place the Validation Method?
Composition and Aggregation Revisited
Composition
Aggregation
Order
Order Line
Has 1
0..*
Attributes
Operations
Customer
Address
Uses 1
1..*
Attributes
Operations

25. Does this Make sense?
Aggregation or Composition?

26. This is an Aggregation
This will need extending to include the parameters

27. The Sequence Diagram

28. The Use Case Diagram

29. The Class Diagram

30. Is it right? Probably not yet
But we now have a mechanism to cross check one diagram with another

31. Exercise Start with an interface component e.g. adding a new record
Plan out the interface on paper
Think about what classes would be required to make this interface work
Have a go at drawing out an initial sequence diagram
Check the triangulation between your use cases and your classes
What use cases / classes might be required