Domain Model• A representation of real-world conceptual

classes in a problem domain. • The core of object-oriented analysis• They are NOT software objects• Created during the elaboration stage• Illustrated as a set of class diagrams

without operations– Conceptual classes– Associations between conceptual classes– Attributes of conceptual classes

Conceptual Model Example

Register

Item

Store

addressname

Sale

date time

Payment

amount

SalesLineItem

quantity

Stocked-in

*

Houses

1..*

Contained-in

1..*

Records-sale-of

0..1

Paid-by

1

1

1

1

1

1

0..1

1

Captured-on

conceptor domain object

association

attributes

Domain Model

• A major distinction between object-oriented and structured analysis is: division by conceptual classes (objects) rather than division by functions

• To identify conceptual classes:– Use a conceptual Class category list– Identify noun phrases– Use analysis patterns done by experts

Conceptual Class Category ListPhysical or tangible objects Events

Specifications, design or description of things

Rules and policies

Places Abstract noun concepts

Transactions/transaction line items Catalogs

Roles of people Records of finance

Containers of things Manuals, books, documents

Things in a container Organizations

Other computer/ electromechanical systems

Noun Phrases

• Identify noun phrases in use-case model • Some are classes, others are attributes

StoreRegister SaleItem

CashPayment

SalesLineItem Cashier Customer

ProductCatalog

ProductDescription

Ledger

Steps to Create Domain Model

• List conceptual classes identified• Draw them in a domain model• Add associations necessary to record

relationship between classes• Add attributes to fulfill requirements

Domain Model Guidelines

• Use the vocabulary of the domain when naming the conceptual classes

• Exclude conceptual classes that are not relevant to the requirements

• Do not include things that are not there in real life

• Conceptual classes are more complex than a number or text (otherwise attribute)

Classes vs. Attributes

Sale

Store

Sale Store

Phone no

Flight

destination

Flight Airport

name

Or ?

Or ?

Specification Conceptual Class

• There is a need to include specification/ description classes that include information about items.

• Used in sales, product and manufacturing domains to include description of a thing

• When all inventory items of a specific product has been sold and the item instance class is deleted, the specification class still remains

Specification Conceptual Class

Item

descriptionpriceserial numberitemID

ProductDescription

descriptionpriceitemID

Item

serial number

Describes Better

Worse

1 *

Specification Conceptual Class

• Use specification conceptual classes when:– There is a need for a description of the item

independent of the current existence of these items in the system

– Deleting instances of things (e.g. items) will result in loss of information that needs to be maintained

– Reduce redundant information

UML vs. Models

• UML describes raw diagram types• Models utilize UML diagrams in certain

context.• For example:

– UML has class diagram (rectangular box)– In Domain model, they are real life conceptual

classes– In Design model, they are software classes

Associations• A relationship between types (instances of

types) that indicates some meaningful and interesting connection

• UML definition: a semantic relationship between two or more classifiers that involve connection among their instances.

• Include associations when:– Knowledge of relationship needs to be stored

for some time– Use “Common association list” to decide

Associations• Lines between classes with association

name on it.

• End points of the line has multiplicity expression indicating numerical relationship between instances of classes

• Default reading direction is left to right, and top to bottom. Or optional reading arrow

• Multiplicity: how many instances of class A can be associated with one instance of class B

Multiplicity Valueszero or more; "many"

one or more

one to 40

exactly 5

T

T

T

T

*

1..*

1..40

5

T3, 5, 8

exactly 3, 5, or 8

Common Association ListA is a physical part of B A is a member of B

A is a logical part of B A is an organizational subunit of B

A is physically / logically contained in B

A is next to B

A is recorded/ logged in B A is an event related to B

A is a description of B A is related to a transaction B

A is a line item of report or transaction

A is owned by B

A uses or manages B A communicates with B

Associations

• It is more important to find conceptual classes than to find associations

• You can have multiple associations between two classes

• Show only important associations

Flight Airport

Flies-to

Flies-from

*

* 1

1

Attributes• A logical data value of an object

• Include attributes in the domain model that the requirements imply to store

• Optionally show the type of the attribute

• Attribute data type should be simple (e.g. string, date, number, boolean)

• If the attribute is not simple, it should be a conceptual class

Attributes

Cashier

namecurrentRegister

Cashier

name

Register

number

Uses

Worse

Better

not a "data type" attribute

1 1

• Relate classes using association NOT attributes (No foreign keys)

Quantities and Units

• Most numeric values have units (e.g. money, weight, length)

• For international software, these quantities should be recorded with their units

• Units are conceptual classes, but it is acceptable to collapse them into data types because they are common

Quantities and UnitsPayment

amount : Number

Payment Quantity

amount : Number

Unit

...

Payment

amount : Quantity

Has-amount1*

Is-in1*

not useful

quantities are pure data values, so are suitable to show in attribute section better

Payment

amount : Money

variation: Money is a specialized Quantity whose unit is a currency

System Sequence Diagram• A picture that shows for a particular use-case

scenario, events that external actors generate, their order and inter-system events.

• Shows input/ output events related to system being described

• The system is treated as a black box

• SSD should be drawn for the main success scenario of the use-case

• Created during the elaboration stage• System events may include parameters

SSD Example

enterItem(itemID, quantity)

:System: Cashier

endSale

makePayment(amount)

a UML loop interaction frame, with a boolean guard expression

external actor to system

Process Sale Scenario

system as black box

the name could be "NextGenPOS" but "System" keeps it simple

the ":" and underline imply an instance, and are explained in a later chapter on sequence diagram notation in the UML

a message with parameters

it is an abstraction representing the system event of entering the payment data by some mechanism

description, total

return value(s) associated with the previous message

an abstraction that ignores presentation and medium

the return line is optional if nothing is returned

total with taxes

change due, receipt

makeNewSale

[ more items ]loop

Use-Case

Use abstract events names:

•enterItem (itemID, quantity)

•Scan (itemID, quantity)

Contracts• Describes detailed system behavior in

terms of state changes of objects in the Domain model after a system operation has been executed

• Done for each complex operation in the System Sequence diagram

• Operation: a specification of a transformation or query that an object may be called to execute

• Writing contracts may suggest changes in the domain model

Contracts Sections• Operation: name of the operation and

parameters• Cross reference: Use case this operation can

occur within• Preconditions: Assumptions about the state of

the system or objects in the domain model before the execution of the operation

• Post conditions: The state of objects in the domain model after the completion of the operation

Contracts• Post conditions: (results)

– Instance creation/ deletion– Changes in attributes– Associations broken or formed

• Steps to write contracts– Identify system operation for SSD– If things are complex and need details – Write contract

Contracts

• Describe real life operations which could be paper-based, not a computer freeing memory

• Example:In many countries, after a person has declared

bankruptcy and seven or ten years have passed, all records of their bankruptcy declaration must be destroyed