Object Oriented Software

Development2009-2010

Modelling business objectsOOSAD Booklet Chapter 4

Lecture: Week 4Brian Farrimond

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Session Aims Representing attributes and operations in

class association diagrams Drawing class association diagrams

derived from business forms

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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

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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

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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

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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

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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

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Modelling business forms

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Chapter 4 example

Typical order form

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Chapter 4 example

First attempt at a class diagram

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Chapter 4 example

First attempt at a class diagram

Problem with duplication of customer data over a number of his orders

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Chapter 4 example

Second attempt at a class diagram

Separate class to hold Customer details

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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

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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

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Chapter 4 example

The new class describes a line on the original order form.

Convention is to name it OrderLine.

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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.

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Chapter 4 example

The new OrderLine class duplicates information about the items being ordered.

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Chapter 4 example

We can remove this duplication by adding a final class.

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Chapter 4 example

We can remove this duplication by adding a final class.

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Exercise 4.7 (page 71)

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Create a class association diagram for this card

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Create a class association diagram for this card

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Create a class association diagram for these forms

Top Grub Order form

Top Grub Invoice form

…. from Database Technology Course.