Object Oriented Software Development Modelling business objects OOSAD Booklet Chapter 4 Lecture: Week 4 Brian Farrimond

2 Session Aims Representing attributes and operations in class association diagrams Drawing class association diagrams derived from business forms

3 Attributes and operations As we gather requirements we find out: what information each class of object needs to record in the form of attributes what the system is supposed to do (we initially record this in use case diagrams) it is the classes that will be required to carry out these tasks we need to identify the operations that they will need to perform to achieve this

4 Attributes and operations in UML The UML class symbol is a box which is divided into three sections class name class attributes class operations (aka methods) Demo in StarUML

5 Operations issues in UML All attributes should have: setter operations to enable other objects to modify attribute values getter operations that enable other objects to discover those values Generally we can omit these from UML diagrams since they can be assumed

6 Operations issues in UML Associations do not require duplicated attributes in UML e.g. do not add a orders attribute to a Customer class - the association line speaks for itself – avoid duplication Bad!! This does the job of modelling what is going on

7 Operations issues in UML Associations do not require duplicated attributes in UML e.g. do not add a orders attribute to a Customer class - the association line speaks for itself – avoid duplication Good! Duplication removed

8 Modelling business forms

9 Chapter 4 example Typical order form

10 Chapter 4 example First attempt at a class diagram

11 Chapter 4 example First attempt at a class diagram Problem with duplication of customer data over a number of his orders

12 Chapter 4 example Second attempt at a class diagram Separate class to hold Customer details

13 Chapter 4 example Now we consider the array. Neater to extract a class containing the details of each item ordered. In Java, objects of this class might be held in an ArrayList

14 Chapter 4 example Now we consider the array. Neater to extract a class containing the details of each item ordered. In C++, objects of this class would be held in a vector

15 Chapter 4 example The new class describes a line on the original order form. Convention is to name it OrderLine.

16 Chapter 4 example What would the equivalent class name be for a line on an Invoice? The new class describes a line on the original order form. Convention is to name it OrderLine.

17 Chapter 4 example The new OrderLine class duplicates information about the items being ordered.

18 Chapter 4 example We can remove this duplication by adding a final class.

19 Chapter 4 example We can remove this duplication by adding a final class.

20 Exercise 4.7 (page 71)

21 Create a class association diagram for this card

22 Create a class association diagram for this card

23 Create a class association diagram for these forms Top Grub Order form Top Grub Invoice form …. from Database Technology Course.