sesi 7 class diagram

Analysis and Design Information System – MTI Fasilkom 2007

Chapter 7 Chapter 7 Structural Modeling

Dana Indra Sensuse ([email protected])Indra Budi ([email protected])

Most slides are adopted from the textbook “Systems Analysis and Design with the Unified Modeling Language, Version 2.0” Alan Dennis, Barbara Wixom, and David Tegarden © 2005


Key Ideas Use-case models provide an external functional view

of the system (what the system does) A structural or conceptual models describe the

structure of the data that supports the business processes in an organization.

The structure of data used in the system is represented through CRC cards, class diagrams, and object diagrams.


Purpose of Structural Models A structural model is a formal way of representing

the objects (things, ideas, and concepts) that are used and created by a business system

Reduce the “semantic gap” between the real world and the world of software The real world tends to be messy, whereas the world of

software must be neat and logical Create a vocabulary for analysts and users to

communicate effectively Structural model also allow the representation of

the relationships between the objects


Essential Elements of a UML Class Diagram

Class Attributes Operations Relationships

Associations Generalization Specialization Aggregation


Classes Templates for creating instances or objects Types of class

Concrete (has objects) Abstract

Another types: the type of real-world thing that it represents Application domain, user interface, data structure, file

structure, operating environment, document, and multimedia classes


Attributes units of information relevant to the description of

the class include only those attributes that are relevant to

the current application “size” for a TV object is not necessary if the application is

concerned only with connections between TV and other objects

do not attempt to include every attribute at the beginning

more attributes can be added when the model is iterated iteration of the model occurs almost at all times, particularly

for large projects


Attributes (Cont) Avoid derivable attributes; instead, create a

function to derive each such attribute “age” can be derived from “birthday” and

“current-date” “total” of all transactions can be dynamically

computed when necessary, rather than storing it somewhere

“discount price” can be computed using current-price and discount factor


Operations The behavior of the class will be defined Action that instances/objects can take Focus on relevant problem-specific

operations, instead of basic operation like create instance, delete instance, access individual attribute, so on.

Will be converted into methods in next phase


Relationships Generalization

Enables inheritance of attributes and operations Ex:

A CUSTOMER class and an EMPLOYEE class can be generalized into a PERSON class by extracting the attributes and operations in common

It is represented with the a-kind-of relationship


Cont.. Generalization (bottom-up approach) Motivated by identifying similarities and

common features among classes“Part-time Instructor” derived from “Instructor” and

“Student” while modeling a department“User” derived from “Customer”, “Bank Manager”

and “Teller” while modeling an ATM system“Material” derived from “Book”, “Journal” and

“Magazine” while modeling a library catalog system


Cont..We can use “specialization” (top-down

approach)“Employee” become “ Secretary”,

“Engineer”“ Student” become “Full-time Student”,

“Part-time Student”“TV” become “Plasma TV”, “Flat Panel

TV”


Relationships (Cont..) Aggregation

Relates parts to wholes A part of or has parts

A door is a part of a carAn employee is a-part of a department

Association Miscellaneous relationships between classes A patient – an appointment


Identify as association if it is not clear whether it is association or aggregation

“Mail” has “Address”“Mail” uses “Address” for delivery“Customer” has “Address”“Customer” resides at “Address”“TV” includes “Screen”“TV” sends information to “Screen”“Customer” is a “Users”


Identify as association if it is not clear whether it is association or aggregation “Mail” has “Address” (aggregation) “Mail” uses “Address” for delivery (association) “Customer” has “Address” (aggregation) “Customer” resides at “Address” (association) “TV” includes “Screen” (aggregation) “TV” sends information to “Screen” (association) “Customer” is a “Users”

(generalization/specialization)


Deriving components of a class diagram from a usecase diagram Actors are potential candidates for classes

Sometimes, an actor may not be modeled as a class

Generalization or specialization between actors will end up in generalization or specialization relationship between the corresponding classes


Two actors will be related if they are connected through a series of use cases The classes corresponding to these actors will

thus have an association The ATM example – the actor “User” is related

to “Account” because of the use cases “deposit” and “update account”


Your Turn What classes, attributes, and operations that would

be required to describe a library system? An librarian

name, birthdate, sex, etc create_account, update, etc

A book title, author, publisher, etc loaned, lost, etc

A catalogue


CLASS-RESPONSIBILITY-COLLABORATION CARDS


Responsibilities Knowing responsibilities are those things

that an instance of a class must be capable of knowing. An instance of a class typically knows the

values of its attributes and its relationship Doing responsibilities are those things that

an instance of a class must be capable of doing An instance of a class can execute its operations


Collaboration Objects working together to service a request Collaborations allow the analyst to think in terms of clients,

servers, and contracts A client object is an instance of a class that sends a request to an

instance of another class for an operation to be executed. A server object is the instance that receives the request from the client

object. A contract formalizes the interactions between the client and server

objects. For example, a patient makes an appointment with a doctor.

This sets up an obligation for both the patient and doctor to appear at the appointed time. Otherwise, consequences, such as billing the patient for the appointment regardless of whether the patient appears, can be dealt out. The contract should also spell out what the benefits of the contract will be, such as a treatment being prescribed for whatever ails the patient and a payment to the doctor for the services provided.


A CRC Card


Back of CRC Card


CLASS DIAGRAMS


Class diagram – basic syntaxClass name

Attributes

Methods

Class name

Attributes

Methods

Class name

Class name

Attributes

Association name

aggregation

specialization

This is a subclass

comments

Aggregate

Component


Details of a class icon

Account

- Account number : Integer

- Balance : Real

- Overdraft : Boolean = true

+ GetAccountId ()

# UpdateBalance (sign : Sign, amt : Integer)

- ChangeOverdraft ()

+ public

- private

# protected

Initial value


Association –syntax

User AccountAccount numberBalanceOverdraft

Get accountID ()

Update balance()

Return balance()

uses

1n

Association label Direction of association

cardinality

Manager

customer

Unary association

Role names

Corporate Account

1

n

{xor}uses


Association Class

User Account

Transaction

Employee Job

Salary


Association Class A piece of information that belongs to both classes in an

association is put into a separate class called “association class” association class is a dependent class that depends on the other two

classes in the association cannot exist independently object of an association class must refer to objects of the other two

classes in the association Example: A “Transaction” object depends on a “User” object and on

an “Account” object.


Example Class Diagram


Class Diagram Syntax

A CLASS

AN ATTRIBUTE

AN OPERATION

AN ASSOCIATION

Class 1

-attribute

+operation ()

Attribute name/derived attribute name

operation name ()

1..* 0..1______verb phrase____


UML suggest for the class name Start with a capital letter Be centered in the top compartment Be written in a boldface font Be written in italics if the class is abstract


More on Attributes Derived attributes

/age, for example can be calculated from birth date and current date

Visibility Public (+) Protected (#) Private (-)


More on Operations Constructor

Creates object Query

Makes information about state available Update

Changes values of some or all attributes


More on Relationships Mean the relationship between one class with

another Multiplicity of relationship

exactly one: 1 zero or more: 0..* one or more: 1..* zero or one: 0..1 specified range: 2..4 multiple disjoint ranges: 1..5,7

Association class


Multiplicity of relationship


Simplifying Class Diagrams When a class diagram is fully populated with all of the

classes and relationships, it become very complex and difficult to interpret

The view mechanism shows a subset of information View based on a particular use case View based on the relationship only or a particular relationship

only (such as association) View based on subset of information such as class name only,

attributes only, or operations only

Packages show aggregations of classes (or any elements in UML)


Object Diagrams


CREATING CRC CARDS AND CLASS DIAGRAMS


Object Identification1. Textual analysis of use-case information

Nouns suggest classes Verbs suggest operations To identify:

Object Attribute Operation Relationship

Creates a rough first cut


Textual Analysis Guideline


Object Identification

2. Common object list Physical/tangible (books, chairs) Incidents (meetings, flight) Roles (doctor, nurse) Interactions (sales transaction)


Object Identification Pattern

Useful groupings of classes that recur in various situations

TransactionsTransaction classTransaction line item classItem classLocation classParticipant class


Steps for Object Identification and Structural Modeling

1. Create CRC cards by performing textual analysis on the use-cases.

2. Brainstorm additional candidate classes, attributes, operations, and relationships by using the common object list approach.

3. Role-play each use-case using the CRC cards.

4. Create the class diagram based on the CRC cards.

5. Review the structural model for missing and/or unnecessary classes, attributes, operations, and relationships.

6. Incorporate useful patterns.

7. Review the structural model.


Application Example:


Textual Analysis: Nouns suggest classes

Step 1. Create CRC cards by performing textual analysis on the use-cases


• Textual Analysis Results: Identified potential classes Customer Search Request CD CD List Review (i.e., CD review information) If further analyse the Maintain Order and Checkout use cases, further potential classes will be identified such as Order Order Item Credit card centre etc

Textual Analysis: Nouns suggest classes



Textual Analysis: Verbs suggest operations: • For each identified class, check the related verbs to identify the operations as well

as the relationships with other classes



• Textual Analysis Result: For Customer Class, the identified operations (i.e., Responsibilities) and the relationship with other classes (i.e., Collaborators) are

Make Search

request Search

request

Select CD for Info

Place Order

CD List

Get Credit Card

Info Exit

Order Credit Card Centre

This forms the front of “Customer class” CRC Card

Not include as it can be included in Search request


Textual Analysis: Verbs suggest operations:


• Textual Analysis Result: Combine “nouns and verbs” analysis, the back of “Customer class” CRC Card can be

Order; Search request; Credit Card Centre



Step 2 and 3. Examine Common Object Lists and Role-play the CRC Cards

2. Brainstorm additional candidate classes, attributes, operations, and relationships by using the common object list approach.

3. Role-play each use-case using the CRC cards.

Possible outcomes: Search request class need having 3 sub-classes: Title Search, Artist Search and Category Search


Step 4. Create the Class Diagram based on the CRC Cards

• Exercise. Suppose the CRC card of Customer class is given as before, create the class diagram based on it. • For customer class, assume that all attributes

are private type whereas all operations are public type

• For other associate classes, only the class names and the relationships with the customer class need to be given


Step 4. Create the Class Diagram based on the CRC Cards

• Solution:

Customer

-First name-Middle initial-Last name-……+Make search req()+Place order()+Get credit info()+Exit()

Credit Card CentreOrder

Search Reg

Check ->

0..*

0..*

place ->

0..*1

Make ->0..*0..*


Step 5, 6 and 7: Review Classes Diagrams, Incorporate Patterns, and Review the Model5. Review the class diagrams and structural model

for any missing and/or redundancy 6. Incorporate useful patterns.

• One possible pattern

7. Review the structural model.


Summary CRC cards capture the essential elements of a class. Class and object diagrams show the underlying structure

of an object-oriented system. Constructing the structural model is an iterative process

involving: textual analysis, brainstorming objects, role playing, creating the diagrams, and incorporating useful patterns.

sesi 7 class diagram

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