CSEB233 Fundamentals of Software Engineering Module 3: Requirements Engineering (Part 2) Badariah...

CSEB233Fundamentals of Software

Engineering

Module 3: Requirements Engineering

(Part 2)

Badariah Solemon 2010

Objectives

1. Identify guidelines of creating requirements analysis models.

2. Explain structured and object-oriented analysis approaches to requirements modelling.

3. Identify three classifications of modelling elements based on object-oriented approach.

4. Introduce use case diagram, activity diagram, class diagram, state diagram, and sequence diagram.


Overview

Activity Action Task

Communication InceptionRequirements Engineering Req. Elicitation

Req. Analysis & NegotiationReq. SpecificationReq. Verification and ValidationReq. Management

Planning

Modeling Requirements ModelingDesign Modeling

Context ModelingTechnical Modeling

Construction

Deployment


Requirements/Analysis Model


• A graphical representations of business processes, the problems to be solved, and the new proposed product (software).

• Objectives:1. To describe software requirements.2. To establish a basis for the creation of a software design.3. To define a set of requirements that can be

validated once the software is built.

• Bridges the gap between a software specification and a software design.

Software specification

Design Model

Analysis Model

Rules of Thumb


• Suggested by Arlow and Neustadt in Pressman (2009):– The model should focus on requirements that are visible within the

problem or business domain. The level of abstraction should be relatively high.

– Each element of the analysis model should add to an overall understanding of software requirements and provide insight into the information domain, function and behavior of the system.

– Delay consideration of infrastructure and other non-functional models until design.

– Minimize coupling throughout the system. – Be sure that the analysis model provides value to all stakeholders. – Keep the model as simple as possible especially if extra diagrams do

not provide new information

Requirements Modeling Principles


• Principle #1. The information domain of a problem must be represented and understood.

• Principle #2. The functions that the software performs must be defined.

• Principle #3. The behavior of the software (as a consequence of external events) must be represented.

• Principle #4. The models that depict information, function, and behavior must be partitioned in a manner that uncovers detail in a layered (or hierarchical) fashion.

• Principle #5. The analysis task should move from essential information toward implementation detail.

*Recap from chapter 4

Domain Analysis


• According to Donald Firesmith in Pressman (2009):“ Software domain analysis is the identification, analysis,

and specification of common requirements from a specific application domain, typically for reuse on multiple projects within that application domain . . . [Object-oriented domain analysis is] the identification, analysis, and specification of common, reusable capabilities within a specific application domain, in terms of common objects, classes, subassemblies, and frameworks . . .”

What is Domain Analysis?


• An on-going SE activity that is not connected to any software project (by domain analyst)

• Involves:1. Defining the domain to be investigated.2. Collecting a representative sample of

applications in the domain.3. Analyzing each application in the sample.4. Developing an analysis model for the objects.

Requirements Analysis Modeling

• Categorized into two main levels of details: 1. Context (conceptual-level) modeling*

• High-level conceptual descriptions of a product and its environment. Must be supplemented with detailed-level models. E.g.: Architectural model

• Usually usable to non-technical people and decision-makers

2. Technical (detailed-level) modeling

* Module 4


Approaches for Technical Modeling1. Structured Analysis

– Considers data and the processes that transform the data as separate entities.

– Includes data models, data flow models and behavioral models

– E.g.: ERD, DFD, state machine model

2. Object-oriented Analysis– model objects, classes, and the relationships and

behavior associated with them.– The industry standard for the OO modeling is known as

Unified Modelling Language (UML) specification and the current available version is 2.2 (OMG, 2009).

– E.g.: use-case diagrams, activity diagrams (swim-lane diagram), sequence diagram, class diagram, state diagram, and etc.

* Relate with generic modeling elements in Part 1.Badariah Solemon 2010

Flow-oriented Modeling


• According to Pressman (2009):– Represents how data objects are transformed as

they move through the system.– data flow diagram (DFD) is the diagrammatic

form that is used.– Considered by many to be an “old school”

approach, but continues to provide a view of the system that is unique—it should be used to supplement other analysis model elements

OO Analysis Approach

• Need to first understand OO concepts, which include objects, classes, attributes, methods, sub-class, super-class, and etc.

• Classifications of OO modeling elements (Pressman, 2005):

1. Scenario-based• to show how end-users interact with the system • e.g.: use-case diagram, activity diagram, swim-lane

diagram


OO Analysis Approach (cont’d)

2. Class-based• to specify classes and objects, attributes, operations,

and associations and dependencies. • e.g.: class diagram, class responsibility collaborator

(CRC) model, collaboration diagram.

3. Behavioral• to model how the system reacts to external event .• e.g.: event-driven use case, state diagram, sequence

diagram.


Scenario-based Modelling: Use Case

• Ivar Jacobson: “[Use-cases] are simply an aid to defining what

exists outside the system (actors) and what should be performed by the system (use-cases).”

• Elements:1. Actor

• a ‘stick figure’ that represent roles of people, other system (database, servers, and legacy systems) or equipment that interact with use cases in the system.


Scenario-based Modeling: Use Case (cnt’d)2. Use case

• an oval shape labeled with the use case name (inside or outside the oval) that represent a complete unit of system functionality.

• A use case may be made up of a set of scenario. Each scenario describes steps that consist of an interaction between the actors and the system.

• Just like DFDs, you can continue to add detail by breaking the uses cases into more use cases.


Use Case: Example #1


University Library System

Use Case: Example #2


• Airline Reservation System

Ticket Clerk

Check In Passenger

Add New Reservation

Cancel Reservation

Airline Reservation System

Relationships of Use Cases


1. Uses – an arrow drawn from use case A to use case B to indicate that in the

process of completing functionality A, functionality B will be performed too.

– For example, in the Airline Reservation System, the ‘Add New Reservation’ use case uses ‘Check Space Availability’ and ‘Record Passenger Information’ use cases.

2. Extends– an arrow drawn from use case A to use case B to indicate that the use

case A is a special way of doing use case B and must be done to complete use case B.

– For example, in the Airline Reservation System, there are two ways to assign a seat either by assigning a window seat or by assigning an aisle seat.

Relationships of Use Cases: Example #1


Airline Reservation System

«uses»

«uses»

«uses»

«uses»

«extends»

«extends»

Ticket Clerk

Check In Passenger

Add New Reservation

Cancel Reservation

Weigh Luggage

Assign Seat

Check Seat Availability

Record Passenger Information

Assign Window Seat

Assign Aisle Seat

B

A

B

A

A

A B

B

Scenario-based Modeling: Activity Diagram• Supplements the use case by providing a graphical

representation of the flow of interaction within a specific scenario.

• Activity diagrams and statechart diagrams are related. – While a statechart diagram focuses attention on an object

undergoing a process (or on a process as an object), an activity diagram focuses on the flow of activities involved in a single process.

– The activity diagram shows the how those activities depend on one another.

• UML’s basic symbols:


Symbol Purpose

To represent an activity

To represent a flow

To represent branching decisions

To indicate all parallel activities within the system.

Activity Diagram: Example #1


• Pressman (2009), pp 162

enter password and user ID

select major function

valid passwords/ ID

prompt for reentry

invalid passwords/ ID

input tries remain

no inputtries remain

select surveillance

other functions may also be

selected

thumbnail views select a specif ic camera

select camera icon

prompt for another view

select specific camera - thumbnails

exit this f unction see another camera

view camera output in labelled window

Scenario-based Modeling: Swimlane Diagram• A variation of activity diagram.• To represent the flow of activities described

by the use-case and at the same time indicate which actor (if there are multiple actors involved in a specific use-case) or analysis class has responsibility for the action described by an activity rectangle.


Swimlane: Example #1

• Pressman (2009), pp 163


enter password and user ID

select major function

valid passwords/ ID

prompt for reentry

invalidpasswords/ ID

input tries

remain

no input

tries remain

select surveillance

other f unct ions may also be

selected

thumbnail views select a specif ic camera

select camera icon

generate video output

select specific camera - thumbnails

exit th isfunct ion

see

anothercamera

homeowner c amera int erf ac e

prompt foranother view

view camera output in labelled window

Swimlane: Example #2

(htt

p://

edn.

emba

rcad

ero.

com

/arti

cle/

3186

3


http://edn.embarcadero.com/article/images/31863/activityno3d.gif

Class-based Modeling: Class Diagram1. Depicts a collection of system’s classes, their

attributes, and the relationships between the classes.

2. A class is an object applicable to a system. – You can think of an object as any person, thing,

place, concept, event, and etc. – Objects have attributes (information stored about

and object or variables for OO programming) and methods or operations (things an object perform).


Class Diagram: Example #1


• To model a class, use a rectangle with three sections: 1. name of the class (top)2. list of attributes (middle)3. methods (bottom).

• Example: – a Student class which has attributes StudentID, Firstname, Lastname,

Email, and ContactNumber. – Student perform operations such as

RegisterCourse, DropCourse, and PrintTranscript.

Student

StudentIDFirstnameLastnameEmailContactNumber

RegisterCourse()DropCourse()PrintTranscript()

Name of class

List of attributes

List of methods

Class Diagram: with Several Classes


• Need to show how they are related to each other. • Two basic types of relationships between classes:

1. Associations• This relationship exists when two classes are related to each

other in any way• You may need to analyse further this relationship by identifying

multiplicity of the association because there is possibility that a students might register for none, one, or several courses.

• Among the potential multiplicity indicators: (next page)• There exist other types of associations such as association class,

aggregation (basic and composition), reflexive associations, and realisation. For further explanation, refer to OMG (2009).

Class Diagram: with Several Classes (cnt’d)


• Example:Registered

0..*0..*attended by

Course

CourseCodeCourseNameCreditHoursFees

Student



Indicator Meaning0..1 Zero or one1 One only0..* Zero or more1..* One or moreN Only n (where n > 1)0..n Zero to n (where n > 1)

1..n One to n (where n > 1)



2. Inheritance/generalisation• Different classes usually share the same attributes

and/or methods. • To avoid repeating the same attributes and/or

methods, you need to take advantage of the inheritance (also known as generalisation) mechanism.

• When class X inherits from class Y, you may say that X is the subclass of Y and Y is the superclass of X.

• UML’s notation for inheritance is a line with upward arrowhead pointing from the subclass to the superclass.



• Example:

* ATM Case Study

PostgraduateProjectTitleThesisSubmitDate



Course

CourseCodeCourseNameCreditHoursFees

Student



Postgraduate ProjectTitleThesisSubmitDate

Undergraduate CreditLimit

Registered

0..*

0..*attended by

Class Diagram: Example


– Models a customer order from a retail catalog (http://edn.embarcadero.com/article/31863)




http://edn.embarcadero.com/article/images/31863/classdiagramno3d.gif

Class-based Modeling: CRC

• Wir (1990): CRC modeling provides a simple means for identifying and organizing the classes that are relevant to system or product requirements.

• Ambler (1995): “A CRC model is really a collection of standard index cards that represent classes. The cards are divided into three sections. Along the top of the card you write the name of the class. In the body of the card you list the class responsibilities on the left and the collaborators on the right.”


CRC: Example





• Pressman (2009) Class:

Description:

Responsibility: Collaborator:

Class:

Description:


Class:

Description:


Class: FloorPlan

Description:


incorporates walls, doors and windows

shows position of video cameras

defines floor plan name/type

manages floor plan positioning

scales floor plan for display

scales floor plan for display

Wall

Camera

Behavioral Modeling

• Make a list of the different states of a system (How does the system behave?)

• Indicate how the system makes a transition from one state to another (How does the system change state?)– indicate event– indicate action

• Draw a state diagram (also known as statechart diagram) or a sequence diagram


The States of a System


• State —a set of observable circum-stances that characterizes the behavior of a system at a given time

• State transition—the movement from one state to another• Event—an occurrence that causes the system to exhibit some

predictable form of behavior• Action—process that occurs as a consequence of making a

transition

State Representations


• In the context of behavioral modeling, two different characterizations of states must be considered: – the state of each class as the system performs its function

and– the state of the system as observed from the outside as

the system performs its function

State Representations (cnt’d)


• The state of a class takes on both passive and active characteristics (de Champeaux et. al. in Pressman (2009)). – A passive state is simply the current status of all of an

object’s attributes.– The active state of an object indicates the current status

of the object as it undergoes a continuing transformation or processing.

State Diagram


• Notations:1. States are rounded rectangles. 2. Transitions are arrows from one state to another. 3. Events or conditions that trigger transitions are written beside the

arrows4. The initial state (black circle) is a dummy to start the action. 5. Final states (2 circles with inner black circle ) are also dummy states

that terminate the action.6. The action that occurs as a result of an event or condition is

expressed in the form /action. • E.g.: Cancel/Quit

State Diagram: Example #1


• http://edn.embarcadero.com/article/31863

http://edn.embarcadero.com/article/images/31863/statediagno3d.gif

Statechart Diagram: Example #2


• State Diagram for the ControlPanel Class (Pressman, 2009)

reading

locked

selecting

password entered

comparing

password = incorrect & numberOfTries < maxTries

password = correct

activation successful

key hit

do: validatePassword

numberOfTries > maxTries

t imer < lockedTime

timer > lockedTime

Behavioral Modeling: Sequence Diagram• An interaction diagram that details how

operations are carried out -- what messages are sent and when.

• Are organized according to time. The time progresses as you go down the page.

• The objects involved in the operation are listed from left to right according to when they take part in the message sequence.


Sequence Diagram


• Each vertical dotted line is a lifeline, representing the time that an object exists.

• Each arrow is a message call. An arrow goes from the sender to the top of the activation bar of the message on the receiver's lifeline.

• The activation bar represents the duration of execution of the message.

• The diagram has a clarifying note, which is text inside a dog-eared rectangle

Sequence Diagram: Example #1


• Pressman (2009)homeowner control panel sensorssystem sensors

system ready

reading

request lookupcomparing

result

password entered

password = correctrequest activation


lockednumberOfTries > maxTries

selecting

timer > lockedTimeA

A

Figure 8.27 Sequence diagram (partial) for SafeHome security function


Sequence Diagram: Example #2


• A sequence diagram for making a hotel reservation• http://edn.embarcadero.com/article/31863

http://edn.embarcadero.com/article/images/31863/sequencediagno3d.gif

Summary

You have been introduced to:1. Guidelines of creating requirements analysis models.2. Two approaches to requirements modelling: structured

and object-oriented analysis approaches.3. Three classifications of modelling elements based on

object-oriented approach.4. Overview of several OO modeling elements such as use

case diagram, activity diagram, class diagram, state diagram, and sequence diagram.


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