Analysis ParalysisWe spend so much time thinking about the

problem and making sure the next step is “perfect” there is a risk that we never actually make the next step.

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

Designing a system is a process of discovery.

Faulty AssumptionsIn 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 Card Identifying duplicates

Consultant Updates Card New data input

Resulting in the following initial use case diagram…

There is a problemBack 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.

Need to Revise the SpecificationThe 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 TableSubject Verb Object ResponseConsultant Inputs Company

NameSystem produces a list of companies with that name

System Finds Company Produces a list of companies with that name

System Lists Employees Produces a list of employees at each company

Consultant Adds Company Company added to the system

Consultant Adds Employee Employee added to the system

Consultant Updates Employee Employee details updated

Consultant Updates Company Company details updated

And the Use Case Diagram

Initial Stab at the Class Diagram

First Go at the Sequence Diagram

Actors Objects Swim lines Messages

Important Questions to AskDo 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 – yesFilterByCompanyNo - no

Revise the Class Diagram

So What Data Comes Back?

We may also find clues to the attributes

Objects must have relationships in the class diagram

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 RevisitedComposition

Aggregation

Order Order LineHas1 0..*

Attributes

Operations

Attributes

Operations

Customer AddressUses1 1..*

Attributes

Operations

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