1. Classes, Sequence Diagrams and Triangulation

2. Simple Class Diagram

3. Relationship Between Layers
Presentation (Use cases)
Middle (Classes)
Data (Entities)

4. A Single Class
Class name
Attributes (Properties)
Operations (Methods)

5. Starting from the Event Table
Subject
Verb
Object
Response
User
Views
Address List
Addresses are listed by the system
Filters
Address list is filtered based on pattern
Adds
Address
Address is added to the system
Updates
Address is updated on the system
Deletes
Address is deleted from the system
System
Validates
Address data is accepted or error is displayed

6. Starting from the Scenario
At the end of each year students have purchased a number of books that are surplus to requirements by the end of the year / course. In order to recycle the books and possibly make a little money a system is required allowing students to sell their books on to students following them on lower years. The application will be web based allowing students to access sales and account details at home. Students will sign up to the site providing contact details. Once authenticated on the system a student will be able to add books that they no longer require. Initially books will be viewable only to the student themselves. To sell on a book the student must take the book to the book shop on the ground floor of Gateway house. The book will be handed to the system administrator (Brenda) who will place the book into stock, provide a receipt for the student and then flag the book on the system as “in stock”. Now that the book is in stock it is visible to other students on the system who may reserve the book for collection. Once reserved the purchasing student must visit the book shop and pay for the book. They will be issued with the book along with a receipt or they have the option of cancelling the transaction if the book was not what they expected (wrong edition of poor condition). As soon as the transaction is completed the seller of the book is notified. They need to visit the bookshop to claim the money paid by the buyer.
Identify the nouns

7. How do we find Associations?
Subject
Verb
Object
Response
Consultant
Inputs
Card
Data accepted by the system
System
Checks
Identifying duplicates
Updates
New data input
Clues may be found looking at subjects and Object

8. Multiplicity
how many of one class may be used by another class

9. Composition (Has relationship)
Can an order line exist without an order?
No – so we indicate a strong relationship
Order
Order Line
Has 1
0..*
Attributes
Operations
Order
Order Line
Has 1
0..*
Attributes
Operations

10. Aggregation (Uses relationship)
Can an address exist without a customer?
Yes - so we express this with a clear diamond
Customer
Address
Uses 1
1..*
Attributes
Operations
Customer
Address
Uses 1
1..*
Attributes
Operations

11. Don’t Forget Collection Classes
1 Collection class allows you to manage many instances of the item class
A good starting point is to consider 1 table needs 2 classes to control it

12. 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

13. The Use Case Diagram

14. The Class Diagram

15. First go at the Sequence Diagram
Actors
Objects
Swim lines
Messages

16. 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

17. 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…

18. The Process Uncertain at first Discuss your products with each other
Develop Individual Event Tables
Draw up initial
use cases
class diagrams
Sequence diagrams
Do they triangulate?