Requirements Analysis

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Chapter 8Analysis Modeling

Adapted by Dan Fleck from:- Roger Pressman’s Slides- http://www.informatics.sussex.ac.uk/users/lb203/se/SE04.pdf- Jochen Rick’s slides from GA Institute of Technology- http://webfuse.cqu.edu.au/Courses/aut2001/95169/

Extra_Examples/DFD_Example_1/- System Analysis and Design slides edited by Yale Braunstein

Coming up: Requirements Analysis

2

Requirements Analysis Requirements analysis

specifies software’s operational characteristics indicates software's interface with other system elements establishes constraints that software must meet

Requirements analysis allows the software engineer (called an analyst or modeler in this role) to: elaborate on basic requirements established during earlier

requirement engineering tasks build models that depict user scenarios, functional activities,

problem classes and their relationships, system and class behavior, and the flow of data as it is transformed.

Coming up: Analysis Phase: What is it?

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Analysis Phase: What is it?

systemdescription

analysismodel

designmodel

Three objectives:

• To describe what the customer requires

• To establish a basis for the creation of a software design

• To define a set of requirements that can be validated once the software is built

Three objectives:




Coming up: Analysis Modeling Approaches

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Analysis Modeling Approaches

Structural analysis: The data: The model defines their attributes and

relationships. The processes that transform the data: The

model shows how they transform the data objects as they flow through the system.

Object-oriented analysis: Focus: Classes and their inter-relationships UML is predominantly object-oriented

But don’t be to dogmatic!Coming up: Elements of the Analysis Model

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Elements of the Analysis Model

Use-case diagrams

Use cases - text

Activity Diagrams

Swim lane diagrams

Scenario-based elements

Class diagrams

Analysis Packages

CRC Models

Collaboration Diagrams

Class-based elements

Data-flow diagrams

Control flow diagrams

Processing narratives

Flow-oriented elements

State diagrams

Sequence diagrams

Behavioral elements

Analysis Model

Coming up: Elements of the Analysis Model

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Elements of the Analysis ModelScenario-based elements



Behavioral elements

Coming up: Class-Based Modeling

High level idea of the system from user’s or a functional perspective

How information flows throughout the system (data and control flow)

How the system responds to external stimuli

Static view of the system and how the different parts are related. Tries to show standard ideas of object oriented development

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Class-Based Modeling Identify analysis classes by examining

the problem statement Use a “grammatical parse” to isolate

potential classes Identify the attributes of each class Identify operations that manipulate the

attributes

Coming up: Grammatical Parsing

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Grammatical Parsing

Write an informal description of the problem. The

customer requirements document is one such

description.

Underline all nouns in the description

Decide which of these are really objects which the

project requires and organize them in related

clusters


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Grammatical ParsingUniversity Bank will be opening in Oxford, Mississippi, in January,

2000. We plan to use a full service automated teller machine (ATM)

system.The ATM system will interact with the customer through a

display screen, numeric and special input keys, a bankcard reader, a

deposit slot, and a receipt printer.Customers may make deposits,

withdrawals, and balance inquires using the ATM machine, but the

update to accounts will be handled through an interface to the

Accounts system.Customers will be assigned a Personal Identification

Number (PIN) and clearance level by the Security system. The PIN can

be verified prior to any transaction.In the future, we would also like to

support routine operations such as a change of address or phone

number using the ATM


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Grammatical Parsing University Bank will be opening in Oxford, Mississippi, in

January, 2000. We plan to use a full service automated teller machine (ATM) system.The ATM system will interact with the customer through a display screen, numeric and special input keys, a bankcard reader, a deposit slot, and a receipt printer.Customers may make deposits, withdrawals, and balance inquires using the ATM machine, but the update to accounts will be handled through an interface to the Accounts system.Customers will be assigned a Personal Identification Number (PIN) and clearance level by the Security system. The PIN can be verified prior to any transaction.In the future, we would also like to support routine operations such as a change of address or phone number using the ATM

Coming up: Typical Classes (a reminder)

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Typical Classes (a reminder) External entities - printer, user, sensor Things - reports, displays, signals Occurrences or events (e.g., interrupt, alarm) Roles (e.g., manager, engineer, salesperson) Organizational units (e.g., division, team) Places (e.g., manufacturing floor or loading dock) Structures (e.g., sensors, four-wheeled vehicles, or computers)

But, how do we select classes?

Coming up: Selecting Classes—Criteria

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Selecting Classes—Criteria

needed services – needed services – operations that change the attributesoperations that change the attributes

multiple attributes – multiple attributes – if it is only one attribute, if it is only one attribute, probably should be part of another classprobably should be part of another class

common attributes – common attributes – common things for all instances of a classcommon things for all instances of a class

common operations – common operations – for all instances of the classfor all instances of the class

essential requirements – essential requirements – appear in the PROBLEM space appear in the PROBLEM space (remember we’re doing analysis modeling!)(remember we’re doing analysis modeling!)

retained information – retained information – information about it must be rememberedinformation about it must be remembered

Coming up: Selecting Classes—Example

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Selecting Classes—Example

needed servicesneeded services

multiple attributesmultiple attributes

common attributescommon attributes

common operationscommon operations

essential requirementsessential requirements

retained informationretained information


ATMUser

Yes

Yes

Yes

Yes

Yes

Yes

PinNum

Yes

No

No

Yes

Maybe

Yes

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Use-case diagrams

Use cases - text

Activity Diagrams

Swim lane diagrams


Class diagrams

Analysis Packages

CRC Models



Data-flow diagrams




State diagrams

Sequence diagrams

Behavioral elements

Analysis Model


Coming up: Data Modeling

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Data Modeling

examines data objects independently of processing

focuses attention on the data domain creates a model at the customer’s

level of abstraction indicates how data objects relate to

one another

Coming up: What is a Data Object?

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What is a Data Object?

ObjectObject ——something that is described by a setsomething that is described by a setof attributes (data items) and that will be of attributes (data items) and that will be manipulated within the software (system)manipulated within the software (system)

each each instanceinstance of an object (e.g., a book) of an object (e.g., a book) can be identified uniquely (e.g., ISBN #) can be identified uniquely (e.g., ISBN #)

each plays a necessary role in the systemeach plays a necessary role in the systemi.e., the system could not function without i.e., the system could not function without access to instances of the objectaccess to instances of the object

each is described by attributes that are each is described by attributes that are themselves data itemsthemselves data items

What are some typical data objects?

Coming up: Typical Data Objects

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Typical Data Objects

external entitiesexternal entities (printer, user, sensor)(printer, user, sensor)thingsthings (e.g, reports, displays, signals) (e.g, reports, displays, signals) occurrences or eventsoccurrences or events (e.g., interrupt, alarm)(e.g., interrupt, alarm)rolesroles (e.g., manager, engineer, salesperson)(e.g., manager, engineer, salesperson)organizational unitsorganizational units (e.g., division, team)(e.g., division, team)placesplaces (e.g., manufacturing floor) (e.g., manufacturing floor)

structuresstructures (e.g., employee record)(e.g., employee record)

Coming up: Data Objects and Attributes

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Data Objects and AttributesA data object contains a set of attributes that A data object contains a set of attributes that act as an aspect, quality, characteristic, or act as an aspect, quality, characteristic, or descriptor of the objectdescriptor of the object

object: automobileobject: automobileattributes:attributes: makemake modelmodel body typebody type priceprice options codeoptions code

How do data objects differ from OO classes or do they?

Coming up: What is a Relationship?

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What is a Relationship?

relationshiprelationship ——indicates “connectedness”; indicates “connectedness”; a "fact" that must be "remembered" a "fact" that must be "remembered" by the system and cannot or is not computed by the system and cannot or is not computed or derived mechanicallyor derived mechanically

several instances of a relationship can exist objects can be related in many different ways

Coming up: Crow’s Foot Style ERD

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Crow’s Foot Style ERD

Coming up: The ERD: An Example

The ERD: Other style’s exist. There are a few, but most are more confusing and less common than Crow’s foot. Depending on who you ask this was invented by Dr. Gordon Everest of Clive Finkelstein.

Teacher Class

Student Address

Teacher teaches 0 to many classes

Classes have 1 and only 1 teacher

Students have 1 to many addressesAn address is for zero to one student (addresses may not be associated with multiple students)

First “thing” denotes optional or mandatory. Second “thing” denotes cardinality (one or many)

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The ERD: An Example

placesplacesCustomerCustomer

requestrequestfor servicefor service

generatesgenerates workworkorderorder

workworktaskstasks

materialsmaterials

consistsconsistsofof

listslists

(1,1)selectedselected

fromfrom

standardstandardtask tabletask table


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Use-case diagrams

Use cases - text

Activity Diagrams

Swim lane diagrams


Class diagrams

Analysis Packages

CRC Models



Data-flow diagrams




State diagrams

Sequence diagrams

Behavioral elements

Analysis Model

Elements of the Analysis ModelOnward to data flow diagrams!

Coming up: Flow-Oriented Modeling

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Flow-Oriented Modeling

Represents how data objects are transformed at they Represents how data objects are transformed at they move through the systemmove through the system

A A data flow diagram (DFD)data flow diagram (DFD) is the diagrammatic form that is the diagrammatic form that is usedis used

Considered by many to be an ‘old school’ approach, flow-Considered by many to be an ‘old school’ approach, flow-oriented modeling continues to provide a view of the oriented modeling continues to provide a view of the system that is unique—it should be used to supplement system that is unique—it should be used to supplement other analysis model elementsother analysis model elements

Coming up: The Flow Model

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The Flow Model

Every computer-based system is an Every computer-based system is an information transform ....information transform ....

computercomputerbasedbased

systemsysteminputinput outputoutput

Coming up: Flow Modeling Notation

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Flow Modeling Notation

external entityexternal entity

processprocess

data flowdata flow

data storedata store

Coming up: External Entity

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External Entity

A producer or consumer of dataA producer or consumer of data

Examples: a person, a device, a sensorExamples: a person, a device, a sensor

Another example: computer-basedAnother example: computer-basedsystemsystem

Data must always originate somewhereData must always originate somewhereand must always be sent to somethingand must always be sent to something

Coming up: Process

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Process

A data transformer (changes inputA data transformer (changes inputto output)to output)

Examples: compute taxes, determine area,Examples: compute taxes, determine area,format report, display graph format report, display graph

Data must always be processed in some Data must always be processed in some way to achieve system functionway to achieve system function

Coming up: Data Flow

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Data Flow

Data flows through a system, beginningData flows through a system, beginningas input and be transformed into output.as input and be transformed into output.

computecomputetriangle triangle

areaarea

basebase

heightheight

areaarea

Coming up: Data Stores

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Data Stores

DataData is often stored for later use.is often stored for later use.

look-uplook-upsensorsensor

datadata

sensor #sensor #

report requiredreport required

sensor #, type, sensor #, type, location, agelocation, age

sensor datasensor data

sensor numbersensor number

type, type, location, agelocation, age

Coming up: Data Flow Diagramming:Guidelines

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Data Flow Diagramming:Guidelines

all icons must be labeled with meaningful names

the DFD evolves through a number of levels of detail

always begin with a context level diagram (also called level 0)

always show external entities at level 0 always label data flow arrows do not represent procedural logic

Coming up: Constructing a DFD—I

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Constructing a DFD—I

review the data model to isolate data objects and use a grammatical parse to determine “operations”

determine external entities (producers and consumers of data)

create a level 0 DFD

Coming up: Level 0 DFD Examples

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Level 0 DFD Examplesuseruser

processing processing requestrequest

videovideosourcesource NTSCNTSC

video signalvideo signal

digitaldigitalvideovideo

processorprocessor

requestedrequestedvideovideosignalsignal

monitormonitor

Coming up: Constructing a DFD—II

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Constructing a DFD—II

write a narrative describing the transform

parse to determine next level transforms

“balance” the flow to maintain data flow continuity

develop a level 1 DFD use a 1:5 (approx.) expansion ratio

Coming up: The Data Flow Hierarchy

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The Data Flow Hierarchy

PPaa bbxx yy

p1p1p2p2

p3p3p4p4 55

aa

bb

cc

ddee

ff

gg

level 0level 0

level 1level 1

Coming up: Example DFD: Level 1

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Example DFD: Level 1

Coming up: DFD: A practical example

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DFD: A practical example

Launched Dec. 11, 1998, the Climate Orbiter plunged too steeply into the Martian atmosphere Sept. 23, 1999, and either burned up or crashed. In an initial failure report released Oct. 15, 2000 the review board blamed the navigation error on a communications foul-up between NASA's Jet Propulsion Laboratory and prime contractor Lockheed Martin.

Launched Dec. 11, 1998, the Climate Orbiter plunged too steeply into the Martian atmosphere Sept. 23, 1999, and either burned up or crashed. In an initial failure report released Oct. 15, 2000 the review board blamed the navigation error on a communications foul-up between NASA's Jet Propulsion Laboratory and prime contractor Lockheed Martin.

Collect,analyze,

generate flightcontrol data

JPL-1

J1 JPL store

Convert datafrom Metric to

English

?

LM1 LM store

Controlspaceflight

LM-1

English data

Transfer of Flight Control DataThis processwas missing

Metric data

Transfer data

?

Who wasresponsible

for this task?

Coming up: Lets Try It

Lets Try It

Lets create a DFD for A carpet cleaning business A web-based order processing system for a

computer store An address book for an iPhone

Coming up: Flow Modeling Notes

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Flow Modeling Notes

each bubble is refined until it does just one thing

the expansion ratio decreases as the number of levels increase

most systems require between 3 and 7 levels for an adequate flow model

a single data flow item (arrow) may be expanded as levels increase (data dictionary provides information)


39

Use-case diagrams

Use cases - text

Activity Diagrams

Swim lane diagrams


Class diagrams

Analysis Packages

CRC Models



Data-flow diagrams




State diagrams

Sequence diagrams

Behavioral elements

Analysis Model


Oh behave!

Coming up: Behavioral Modeling

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Behavioral Modeling The behavioral model indicates how software will

respond to external events or stimuli. To create the model, the analyst must perform the following steps:

Evaluate all use-cases to fully understand the sequence of interaction within the system.

Identify events that drive the interaction sequence and understand how these events relate to specific objects.

Create a sequence diagram for each use-case. Build a state diagram for the system. Review the behavioral model to verify accuracy and

consistency.

Coming up: State Representations

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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

Coming up: State Diagram for the ControlPanel Class

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State Diagram for the ControlPanel Class

reading

locked

selecting

passwordentered

comparing

password = incorrect& numberOfTries < maxTries

password = correct

activation successful

key hit

do: validatePassword

numberOfTries > maxTries

timer < lockedTime

timer > lockedTime

Coming up: State Diagram Details

State Diagram Details

Coming up: The States of a System

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State Name (verb in current tense)

(Optional) actions happening during state

Name Examples:sortingvalidatingupdating status…

[age > 20]

[age <= 20]

Guards: Use to describe event that causes a state transition happens (ALL transitions should have guards)

[age <= 20]/setFlag(false)

Action: If something happens while transitioning to another state. (Optional)

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The States of a System state—a set of observable

circumstances 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

Coming up: Behavioral Modeling

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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 or a sequence diagram

Coming up: State Diagram - Lets Try It!

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State Diagram - Lets Try It!You are designing a traffic light system for this intersection.

Draw a state diagram showing the different states and how they transition.

North

South

East

West


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Use-case diagrams

Use cases - text

Activity Diagrams

Swim lane diagrams


Class diagrams

Analysis Packages

CRC Models



Data-flow diagrams




State diagrams

Sequence diagrams

Behavioral elements

Analysis Model


Coming up: Object Oriented Analysis (OOA)

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Object Oriented Analysis (OOA)

The intent of OOA is to define all classes (and the relationships and behavior associated with them) that are relevant to the problem to be solved. For that, a number of tasks must occur:

1. Classes must be identified (i.e., attributes and methods)

2. A class hierarchy is defined

3. Object-to-object relationships should be represented

4. Object behavior must be modeled

5. Tasks 1 through 4 are reapplied iteratively

Coming up: Object-Oriented Concepts

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Object-Oriented Concepts What are the basic object oriented

concepts?


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Object-Oriented Concepts What are the basic object oriented

concepts? Classes and objects Attributes and operations Encapsulation and instantiation Inheritance

The analysis model is designed to help you make “good” choices


51

Object-Oriented Concepts What helps you determine if

something should be a class or an attribute?

What helps you determine needed operations?

How does the analysis model make sure your requirements are correct?


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Elements of the Analysis ModelScenario-based elements



Behavioral elements

Coming up: Analysis Model Rules of Thumb

High level idea of the system from user’s or a functional perspective

How information flows throughout the system (data and control flow)

How the system responds to external stimuli

Static view of the system and how the different parts are related. Tries to show standard ideas of object oriented development

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Analysis Model Rules of Thumb

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 certain that the analysis model provides value to all

stakeholders. Keep the model as simple as it can be.

Coming up: Analysis Phase: What is it?

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Analysis Phase: What is it?

systemdescription

analysismodel

designmodel

Three objectives:




Three objectives:




Coming up: Writing the Software Specification

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Writing the Software Specification

Everyone knew exactly what had to be done until someone wrote it down!

Coming up: Specification Guidelines

Read the last three

slides on your own

Read the last three

slides on your own

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Specification Guidelinesuse a layered format that provides increasing detail as the "layers" deepen

use consistent graphical notation and apply textual terms consistently (stay away from aliases)

be sure to define all acronyms

be sure to include a table of contents; ideally, include an index and/or a glossary

write in a simple, unambiguous style (see "editing suggestions" on the following pages)

always put yourself in the reader's position, "Would I be able to understand this if I wasn't intimately familiar with the system?"


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Specification GuidelinesBe on the lookout for persuasive connectors, ask why? keys: certainly, therefore, clearly, obviously, it follows that ...

Watch out for vague terms keys: some, sometimes, often, usually,ordinarily, most, mostly ...

When lists are given, but not completed, be sure all items are understood keys: etc., and so forth, and so on, such as

Be sure stated ranges don't contain unstated assumptions e.g., Valid codes range from 10 to 100. Integer? Real? Hex?

Beware of vague verbs such as handled, rejected, processed, ...

Beware "passive voice" statements e.g., The parameters are initialized. By what?

Beware "dangling" pronouns e.g., The I/O module communicated with the data validation module and its contol flag is set. Whose control flag?


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Specification GuidelinesWhen a term is explicitly defined in one place, try substituting the definition forother occurrences of the term

When a structure is described in words, draw a picture

When a structure is described with a picture, try to redraw the picture to emphasize different elements of the structure

When symbolic equations are used, try expressing their meaning in words

When a calculation is specified, work at least two examples

Look for statements that imply certainty, then ask for proof keys; always, every, all, none, never

Search behind certainty statements—be sure restrictions or limitations are realistic

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Requirements Analysis

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