Developing Domain ModelsDeveloping Domain Models

The most important UML model

The VisionThe Vision

Soft Systems Models

Use Cases

Interaction Models

Class Diagrams

Programs

Databases

BusinessComputing

What is a Domain Model?What is a Domain Model?

• Later we will see that the class diagram in UML is a design for software and databases

• The class diagram is based on a model of the real world which we will call the Domain Model

• Our domain model is a class diagram specified at a level of abstraction that models a real world situation

• We will call this a domain model to distinguish it from the more detailed class diagrams that can be used to generate program code

classes consist ofclasses consist of

• A name, e.g. customer

• Attributes, e.g. name and address

• Operations, e.g. order, pay for goods

Representing classesRepresenting classes

Customer

nameaddress

orderreceive goodspayreturn goods

Invoice

customerIDcustomer addressinvoice linesvattotal

print

Relationships / AssociationsRelationships / Associations

• Provide lines of communication between classes

• Are used to construct complex systems

RelationshipsRelationships

dog bites postman

man orders meal

driver car

Relationship typesRelationship types

• Relationships can fall into any of three basic types

often referred to as the relationship’s Multiplicity.

• One to one

• One to many

• Many to many

• Each end of a relationship on a domain model can

have a note displaying a symbol or number which

describes the kind of relationship

Relationship notationRelationship notation

Notation Meaning

1 One at this end

1..n One or more at this end

3..n Three or more at this end

5 Exactly five at this end

0..n Zero or more at this end

7..10 Seven to ten at this end

One-to-one RelationshipsOne-to-one Relationships

• Modelled by a line between the two classes

• No arrows, so either class may communicate with the

other

• You can label the relationship (but you don’t have to) No label at an end of a relationship indicates a 1

• You may also wish to name the relationship

man womanmarried

Directional relationshipsDirectional relationships

Arrows indicate that one class communicates with

another, but not the other way

canarylittle old lady cateatown

One-to-many RelationshipsOne-to-many Relationships

• These are modelled by a labelled straight line, with a label at the end indicating the “many” end of the relationship

• A label must be used to indicate how many

• No label implies one class at the end of the relationship

• e.g. a player plays for one football team. There are at least 11 players for a given football team.

player team

111..n 111..n

One to many relationshipsOne to many relationships

A customer has zero or more invoices

customer invoice

0..n0..n

One to many relationshipsOne to many relationships

• A juggler has two hands and a hand can hold zero or one ball

juggler hand

22

jugglingBall0..1hold 0..1

Many-to-many RelationshipsMany-to-many Relationships

• These are modelled by a straight line, with a label at each end

• A lubricant may be recommended for one or more engines, and an engine may have one or more lubricants recommended for it

lubricant engine

1..n1..n

recommendation

1..n 1..n

Many-to-many RelationshipsMany-to-many Relationships

• A postman might be bitten by zero or more dogs, and a dog may bite zero or more postmen

postman dog

0..n0..n 0..n0..n

Many-to-many RelationshipsMany-to-many Relationships

• A suitor may court one or more princesses, and a princess may have zero or more suitors

suitor Princess

1..n0..n0..n 1..n

Many-to-many RelationshipsMany-to-many Relationships

• Frogs and princesses have relationships too!

frog Princess

0..11..n 0..11..n

a domain modela domain model

• domain models consist of a number of related classes

patient

doctor

0..n0..n

refer

specialist

0..n

0..n

0..n

0..n

1..n1..n

use

1..n 1..n

treat

A domain modelA domain model

buttonlift

1..n1..n

call

floor

1..2

1..n

1..n

1..n

1..n

service

0..1

0..n0..n

0..1at

1..2

a domain modela domain model

flower Wolf

Grandma

eat

Red Riding Hood

1..n1..n

WoodMan

kill

rescuefetch

talk

a domain modela domain model

shopping home page

product page

1..nshopping

basket page1..n

1..n

1..n

shopping basket

1..n1..n

order1..n1..n

a domain modela domain model

Module

Coursework Submission

Student1..n1..n

1

Lecturer

1..n1..n

Assessment

2

1..n1..n

1..n

exam script

1..n1..n

1..n1..n

2

1..n

Other types of RelationshipOther types of Relationship

Inheritance and Aggregation

Remember Daisy?Remember Daisy?

Daisy: Cow

Colour = BrownPattern = noneWeight = 400kg

Cow

NameWeightPattern

Produce MilkGo “Moo”Eat Grass

ObjectClass

Thelma and MadgeThelma and Madge

Thelma Madge CowName

WeightPattern

Produce MilkGo “Moo”Eat Grass

Daisy

All belong to the class COW

IntroducingIntroducing

Silver

Horse

NameWeightHeight

RunsJumps

Eat Grass

andand

Dolly

Sheep

NameWeight

Wool colour

Goes “Baah”Produces wool

Eat Grass

Madge, Silver and DollyMadge, Silver and Dolly

Share some attributes and operations

CowName

WeightPattern

Produce MilkGo “Moo”Eat Grass

HorseName

WeightHeight

RunsJumps

Eat Grass

SheepName

WeightWool colour

Goes “Baah”Produces wool

Eat Grass

New ClassNew Class

AnimalName

Weight

Eat Grass

This class contains all the shared attributes and operations of the three other classes

The concept of inheritanceThe concept of inheritanceIf we were to model sheep, cows and horses in one diagram we may well use the new animal class to make the process much more economical. The diagram would then look like this:

AnimalName

Weight

Eat Grass

Cow

Pattern

Produce milkGo “moo”

Sheep

Wool colour

Produce woolGo “Baah”

Horse

Height

JumpRun

The concept of inheritanceThe concept of inheritance

• By doing this we are saying that the Cow, Horse and Sheep classes can INHERIT all the attributes from the animal class.

• In this instance, the animal class is known as a SUPERCLASS and the Cow, Horse and Sheep classes are SUB-CLASSES

Superclass

Sub-class Sub-class

The concept of inheritanceThe concept of inheritance

• So in addition to the Horse

having Height as an attribute,

it also inherits Name and

Weight.

• And as well as having the

operations Jump and Run, it

also inherits Eat Grass

AnimalName

Weight

Eat Grass

Horse

Height

JumpRun

InheritanceInheritance

• Classes can be arranged in inheritance hierarchies

• A class inherits operations and attributes from its parent

• This is one of the underlying mechanisms for providing for design and code re-use

• We use a special relationship to indicate this on the domain model:

parentchild

Inheritance - exampleInheritance - example

student

coursemodules taken

person

nameaddress

Lecturer

modules taught

Suppose we have already defined the notion of person as an objectWe now want to add a new kind of person - a student

So we make use of the existing person definition, and introduce an inheritance relationshipNow students have the same attributes as person, plus some new ones of their ownAnd likewise, we can create a new type of person, a lecturer, that inherits from person

Relationships are inheritedRelationships are inherited

student

coursemodules taken

Lecturer

modules taught

person

namecompanyaddress

Suppose that we find that person and company share addressWe can split address out into a separate object And then add in some relationships Now if we add in a student And make the student inherit from person Then students have addresses too by inheritance And we can do the same for a lecturer

Inheritance - jugglingInheritance - jugglingjuggleObject

weight

throw()catch()pickUp()drop()

jugglingBall

club

rotationSpeed

ball

diameter

tennisBall

bounce()

egg

smash()

Consider our juggling objects

There are three types of thingto juggle.

And balls can be further refined

So tennis balls can be bounced, thrown, caught, picked up and dropped

Inheritance goes all the way down the hierarchy

Inheritance - enginesInheritance - engines

engine

cylindersname

start()stop()

Diesel Engine

preheat()

Petrol Engine

spark plugs

Steam Engine

boiler

light()

Inheritance - governmentInheritance - government

Government Organisation

tax()elect representatives()

Local Government

Provide Service()

Central Government

Legislate()

Regional Government

Set Transport Policy()

Metropolitan Government

Set Education Policy()

Inheritance - magnitudeInheritance - magnitude

Magnitude

compare()print()

Coordinate

add()subtract()multiply()

Integer

add()subtract()multiply()

Why not push add, subtract, multiply up the hierarchy?

Because, though they have the same name, they do different things!

Multiple inheritanceMultiple inheritance

salt

solvent solution

An object can get operations and attributes from two or more other objects

Problems of multiple inheritanceProblems of multiple inheritance

• Conflict on inherited attributes and methods

• Complexity

• In general avoid it - mostly it can be worked around in better ways (see delegation, later)

Finding inheritanceFinding inheritance

• If two things are similar, are there common aspects (e.g. employee and customer)

• If you want to create something new, is there something similar to inherit from (e.g. web customer might be a special case of customer)

AggregationAggregation

• Objects can be made up of other objects, e.g. a car is

made up of engine, body, transmission and wheels.

• Aggregation hierarchies are used to describe this

• There is no inheritance in an aggregation hierarchy

• We use a special relationship to indicate aggregation

wholepart

Aggregation - exampleAggregation - example

hand

juggler

foot

22

A juggler has hands and feetHands and feet are “part of” a jugglerAnd there are two of each (normally)

Aggregation - lubricantsAggregation - lubricants

lubricant

base oil additive package

dispersant antioxidant vi improverdetergent

Aggregation - PathwaysAggregation - Pathways

Pathway

Module

Lecture Assessment

Finding aggregationFinding aggregation

• Break complicated objects into their parts

• Build objects out of existing objects

Inheritance and AggregationInheritance and Aggregation

• Are important types of relationships

• Allow developers to re-use existing designs and

implementations

• Adds more meaningful structures

• Reduces the amount of development and design

time that is needed.

DelegationDelegation

• Operations on an object can be delegated to

component objects (e.g. starting a car is delegated to

the engine, which in turn might be delegated to the

starter motor and ignition system)

• Delegation is another way of introducing sharing.

Objects with common components can share the

implementation of those components.

• We shall be looking at how objects call each other in

more detail later

Key PointsKey Points

• Inheritance and aggregation are special types of

relationship

• Inheritance passes attributes and operations

• Aggregation does not pass attributes and operations

• Aggregate objects delegate functionality to their parts

• Inheritance allows for re-use of designs and

implementation

domain modellingdomain modelling

• The principle output of OOAD is the domain model

• The domain model consists of all classes and

relationships

• It defines the static structure of a system

• It evolves and is extended throughout the

development life-cycle

domain modellingdomain modelling

• The domain model will expand and increase in detail as analysis and design progresses

• The first model should only consider real world elements and leave out design and implementation details

• Dynamic modelling will be used to extend the domain model

• Design will add new classes such as interfaces and control classes, and partition the system using concepts such as packages and components

• Implementation will add further detail

TutorialTutorial

• Working in groups we will develop a number of domain models and compare the results