Sequence Diagrams

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

Watch out for Red Herrings

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. email address.

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

Resulting in the following initial use case diagram…

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!

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. email address.

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

And the Use Case Diagram

And Probably the Class Diagram

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 objects support our use cases…

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

First go at the Sequence Diagram Actors Objects Swim lines Messages

Important Questions to Ask Do we have an actor on the use case that matches the sequence diagram? Yes! Do we have a class that allows us to create the Companies object? Yes! Do we have methods in the class that are able to handle the messages? FilterByCompanyName – yes FilterByCompanyNo - no

Revise the Class Diagram

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

Extending the Sequence Diagram Do we have an operation to support this message?

Revise the Class Diagram

What About Validation?

Modify the Use Case Diagram

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

Does this Make sense? Aggregation or Composition?

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

The Sequence Diagram

The Use Case Diagram

The Class Diagram

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

Exercise Start with an interface component e.g. adding a new record Plan out the interface on paper Think about what object(s) 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