COMP2007-Unified modelling language

Question 0

UML Diagrams

Answer 0

Class diagrams
- describe classes & their relationships

Inreraction diagrams
- show behaviour of sys in terms of how objects interact

State and activity diagrams
- show how systems behave internally

Component and deployment diagrams
- show how sys components are arranged logically & physically

Question 1

UML

Answer 1

Standard graphical language for modelling oo sw

Not a methodology, assists in dev

Question 2

UML Class diagrams

Answer 2

Classes
- represent the types of data themselves

Associations
- linkages btwn instances of classes

Attributes
- simple data found in classes & their instances

Operations
- represent the functions performed by classes & instances

Generalisations
- group classes into inheritance hierarchies

Question 3

UML Code

Answer 3

------------
| Student |     public class 
------------       Student
| + name |         {
| + ID       |          public int 
========         name;
                          Public int ID;
                         }

Question 4

Design process affects

Answer 4

Development rime

Software quality

Ease of maintenance

Question 5

UML models help during different stages and with different purposes

Answer 5

Sys analysis model
- during analysis ph to learn bout domain

Sys arch model
- high level abstract classes representing sys arch and interfaces

Detailed des model
- refine analysis model till material in form that can be implemented by programmers

Question 6

Dinding classes + developing class diagrams

Answer 6

Identify classes

Add associations and attributes

Find generalisations

List main responsibilities of each class

Decide on specific operations

Iterate till model ok

Question 7

Identifying generalisations & interfaces

Answer 7

Find generalisations
- bottom up-group similar to create super class

-top down- look for more general classes 1st, specialise them if needed

Create an interface io super class
If
Classes dissimilar except few common operations
1 or more already have own superclass
Diff implementations of same class might b available

Question 8

Coupling & cohesion

Coupling

Answer 8

Coupling - number of dependencies between two systems

Loosely coupled systems -> independent; modification to one has little effect on another

Low coupling is good; reduce impact of changes

Question 9

Coupling & cohesion

Cohesion

Answer 9

Cohesion refers to dependencies within a module’s internal elements

High cohesion means that the module is focused in purpose, understandable, manageable

Question 10

Low coupling good

Answer 10

High cohesion good

Question 11

Coupling

Answer 11

Measure of how strongly classes interact

A has an attribute of B
A inherits from B
A calls on the service of a B object
A has a method which references B

Question 12

Disadvantages of high coupling

Answer 12

Change in one class ripples to others

Difficult to understand class in isolation

Difficult to reuse class because dependabt class must also be used

Question 13

Cohesion

Answer 13

Measure of how strongly related and focused the responsibilities of single classes are

It is decreased when;
Responsibilities (operations) of a class have little in common

Operations do many varied activities, often using varied data.

Question 14

Disadvantages of weak cohesion

Answer 14

Difficult to understand

Difficult to maintain as constantly affected by changes

Difficult to reuse as most applications wont need a random set of operations attached to a class

Question 15

Class responsibility collaboration cards

Answer 15

One per candidate class

Class Superclasses
Subclasses
Responsibilities Collaborations

Using a small card keeps the complexity of design to a minimum

Question 16

Class responsibilities

Answer 16

Assign responsibilities to each class based on Services it provides and Data it keeps

• set & getting values of attributes
• creating & initialising new instances
• loading and saving to persistent storage
• destroying instances
• copying, concerting, transforming, transmitting or outputting
• computing numerical results
• navigating & searching
  Interactions with other classes
  Classes with too many responsibilities should b divided

Question 17

Class responsibility-more consiserations

Answer 17

Stereotype of class ("Interface" used in java)
Super/sub class responsibilities
Collaborators
- providing information
- providing a service

Ask
Can this class fulfill this responsibility itself

If not what does it need

From what other class can it acquire what it needs

Question 18

Problem statement

Answer 18

Get nouns

Consider them for candidate objects

Get verbs

Consider them for relationships
Also get assumptions-tacit knowledge

Question 19

Make an initial clas diagram

Answer 19

Just with boxes with nouns and lines with verbs connecting them

Question 20

Make a sequence diagram

Answer 20

Usage scenario

Interaction diagram