Unit 4

Unit – 4Unit – 4 Requirements Requirements EngineeringEngineering

Requirements Engineering Requirements Engineering TasksTasks

(A) Inception(A) Inception—ask a set of questions that establish —ask a set of questions that establish …… basic understanding of the problembasic understanding of the problem the people who want a solutionthe people who want a solution the nature of the solution that is desired, and the nature of the solution that is desired, and the effectiveness of preliminary communication and the effectiveness of preliminary communication and

collaboration between the customer and the developercollaboration between the customer and the developer(B) Elicitation(B) Elicitation—elicit requirements from all —elicit requirements from all

stakeholdersstakeholders(C) Elaboration(C) Elaboration—create an analysis model that —create an analysis model that

identifies data, function and behavioral identifies data, function and behavioral requirementsrequirements

(D) Negotiation(D) Negotiation—agree on a deliverable system —agree on a deliverable system that is realistic for developers and customersthat is realistic for developers and customers

(E) Specification(E) Specification—can be any one (or more) of the —can be any one (or more) of the following:following: A written documentA written document A set of modelsA set of models A formal mathematical modelA formal mathematical model A collection of usage scenarios A collection of usage scenarios A prototypeA prototype

(F) Validation(F) Validation—a review mechanism that looks for—a review mechanism that looks for errors in content or interpretationerrors in content or interpretation areas where clarification may be requiredareas where clarification may be required missing informationmissing information inconsistencies (a major problem when large products or inconsistencies (a major problem when large products or

systems are engineered)systems are engineered) conflicting or unrealistic (unachievable) requirements. conflicting or unrealistic (unachievable) requirements.

(G) Requirements management(G) Requirements management

Building the Analysis ModelBuilding the Analysis Model

Elements of the analysis modelElements of the analysis model Scenario-based elementsScenario-based elements

Functional—processing narratives for software Functional—processing narratives for software functionsfunctions

Use-case—descriptions of the interaction Use-case—descriptions of the interaction between an “actor” and the systembetween an “actor” and the system

Class-based elementsClass-based elements Class DiagramClass Diagram

Behavioral elementsBehavioral elements State diagramState diagram

Flow-oriented elementsFlow-oriented elements Data flow diagramData flow diagram

Class DiagramClass Diagram

Sensor

name/id type location area characteristics

identify() enable() disable() reconfigure()

State DiagramState Diagram

Reading Commands

System Status=“Ready”Display msg=“enter cmd”

Display status=steadyDo: poll user input panel

Do: read user inputDo: interpret user input

Data ModelingData Modeling

Analysis modeling often begins with data Analysis modeling often begins with data modeling.modeling.

The Data Modeling:-The Data Modeling:- examines data objects independently of examines data objects independently of

processingprocessing focuses attention on the data domainfocuses attention on the data domain creates a model at the customer’s level of creates a model at the customer’s level of

abstractionabstraction indicates how data objects relate to one indicates how data objects relate to one

anotheranother

What is a Data Object?What is a Data Object?

manipulated within the software (system)manipulated within the software (system)

——something that is described by a setsomething that is described by a setObjectObjectof attributes (data items) and that will be of attributes (data items) and that will be

Typical ObjectsTypical Objectsexternal 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)

placesplaces (e.g., a warehouse) (e.g., a warehouse) structuresstructures (e.g., a file)(e.g., a file)

Data AttributesData Attributes

A data object contains a set of A data object contains a set of attributes that act as an aspect, attributes that act as an aspect, quality, characteristic, or descriptor of quality, characteristic, or descriptor of the objectthe object

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

What is a Relationship?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 several instances of a relationship can existrelationship can exist

objects can be related in objects can be related in many different waysmany different ways

Cardinality and ModalityCardinality and Modality

“ “ Cardinality is the specification of the Cardinality is the specification of the number of occurrences of one object that number of occurrences of one object that can be related to the number of can be related to the number of occurrences of another object”occurrences of another object”

“ “ The modality of a relationship is ‘0’ if there The modality of a relationship is ‘0’ if there is no explicit need for the relationship to is no explicit need for the relationship to occur or the relationship is optional. The occur or the relationship is optional. The modality is ‘1’ if an occurrence of the modality is ‘1’ if an occurrence of the relationship is mandatory.”relationship is mandatory.”

Flow-Oriented ModelingFlow-Oriented Modeling

Represents how data objects are Represents how data objects are transformed as they move through the transformed as they move through the systemsystemFlow Modeling NotationFlow Modeling Notation

external entityexternal entity

processprocess

data flowdata flow

data storedata store

Gane and Sarson Symbol Set

Description Yourdon Symbol Set

Data Source and Destination symbol depicts external entities or portrays source and destination of data flow.Origin or Destination

Basic DFD Symbols

Bubble/circle symbol may represent the whole system (context diagram), internal entity (physical DFD) or process (logical DFD) of a particular system.

Storage symbolrepresents data

storage where data are being stored.

It can also represent a view or portion of company’s database.

Data flow symbol indicates a flow of data or documents into or outside from the system; flow of data between the entities (in physical DFD) and flow of data between processes (in logical DFD).

or or

External EntityExternal EntityA producer or consumer of dataA producer or consumer of data

Examples: a person, a device, a sensorExamples: a person, a device, a sensorAnother 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

ProcessProcessA 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

Data FlowData 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

Data StoresData 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

Data Flow Diagramming:Data Flow Diagramming:GuidelinesGuidelines

all icons must be labeled with all icons must be labeled with meaningful namesmeaningful names

the DFD evolves through a number the DFD evolves through a number of levels of detailof levels of detail

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

always show external entities at always show external entities at level 0level 0

always label data flow arrowsalways label data flow arrows

(1) Constructing a Data Flow (1) Constructing a Data Flow ModelModel

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

determine external entities (producers and determine external entities (producers and consumers of data)consumers of data)

create a level 0 DFDcreate a level 0 DFDLevel 0 DFD ExampleLevel 0 DFD Example

useruserprocessing processing

requestrequest

videovideosourcesource

video signalvideo signal

digitaldigitalvideovideo

processorprocessor

requestedrequestedvideovideosignalsignal

monitormonitor

Constructing LevelsConstructing Levels write a narrative describing the transformwrite a narrative describing the transform parse to determine next level transformsparse to determine next level transforms ““balance” the flow to maintain data flow balance” the flow to maintain data flow

continuitycontinuity develop a level 1 DFDdevelop a level 1 DFD

level level 11

PPaa bbxx yy

p1p1p2p2

p3p3p4p4 p5p5

aa

bb

cc

ddee

ff

gg

level 0level 0

Flow Modeling NotesFlow Modeling Notes

each bubble is refined until it does just each bubble is refined until it does just one thingone thing

the expansion ratio decreases as the the expansion ratio decreases as the number of levels increasenumber of levels increase

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

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

DFDs: A Look AheadDFDs: A Look Ahead

Maps intoMaps intoanalysis modelanalysis model

design modeldesign model

DFD ExampleDFD Example In the following example, a DFD will be created based In the following example, a DFD will be created based

on a paragraph about ABC Records Co.’s method of on a paragraph about ABC Records Co.’s method of receiving and filling orders.receiving and filling orders.

In this example, the information necessary to create In this example, the information necessary to create the DFD is provided for us. In Real Life, this the DFD is provided for us. In Real Life, this information comes from extensive interviewing, information comes from extensive interviewing, document gathering, and other research.document gathering, and other research.

Depending upon the system being studied, the number Depending upon the system being studied, the number of people working on it, etc., the development of a of people working on it, etc., the development of a detailed DFD can take anywhere from a few hours to detailed DFD can take anywhere from a few hours to several months (paid for by your client with NO CODE several months (paid for by your client with NO CODE TO SHOW FOR IT). Yet it is a very standard and TO SHOW FOR IT). Yet it is a very standard and meaningful part of system documentation.meaningful part of system documentation.

DFD ExampleDFD ExampleABC Records is a mail-order company that distributes CDs and tapes at discount price to record-club members. When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file. If the sender is not a member, the clerk returns the order along with a membership application form. If the customer is a member, the clerk verifies the order item data by checking the Item file. Then the clerk enters the order data and saves it to the Daily Orders file. The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment.

DFD Example - Step 1DFD Example - Step 1

FIRST SENTENCEFIRST SENTENCE::ABC Records is a mail-order company that ABC Records is a mail-order company that

distributes CDs and tapes at discount price to distributes CDs and tapes at discount price to record-club members.record-club members.

RESULTRESULT: initial title: initial title

ABC Records order processingABC Records order processing


SECOND SENTENCESECOND SENTENCE::When an order processing clerk receives an When an order processing clerk receives an

order form, he or she verifies that the sender is order form, he or she verifies that the sender is a club member by checking the Member file.a club member by checking the Member file.

RESULTRESULT: ABC Records Order Processing: ABC Records Order Processing

EE-1

R e c o rd C lu bM e m b e r

1

Verify m em bers tatus

O R Clerk

EE-2

C u s to m e r(n o n -m e m b e r)

D -1 M e m b e r M a s t e ro rd e r me m b e rd a t a


THIRD SENTENCETHIRD SENTENCE::If the sender is not a member, the clerk returns the If the sender is not a member, the clerk returns the

order along with a membership application form.order along with a membership application form.


EE-1


1


O R Clerk

EE-2

C u s t o m e r(n o n -m e m b e r)

D -1 M e m b e r M a s t e ro rd e r me m b e rd a t a

n o n -m e m b e r o rd e ra n d a p p lic a t io n fo rm

DFD Example - Step 4DFD Example - Step 4FOURTH SENTENCEFOURTH SENTENCE::If the customer is a member, the clerk verifies If the customer is a member, the clerk verifies

the order item data by checking the Item file. the order item data by checking the Item file.


EE-1


1


O R Clerk

EE-2


D -1 M e m b e r M a s t e rme m b e rd a t a


2

Verify orderitem data

O R Clerk

m e m b e ro rd e r

D -2 It e m M a s t e rit e md a t a


FIFTH SENTENCEFIFTH SENTENCE::Then the clerk enters the order data and saves it to Then the clerk enters the order data and saves it to

the Daily Orders file.the Daily Orders file.RESULTRESULT: ABC Records Order Processing: ABC Records Order Processing

EE-1


1

Ver ify m em bers tatus

O R Clerk

EE-2


D -1 M e m b e r M a s t e r


2

Ver ify orderitem data

O R Clerk

m e m b e ro rd e r

D -2 It e m M a s t e r

3

Enter orderinto D aily

O rdersO R Clerk

v e rifie dm e m b e r

o rd e r

D -3 D a ily O rd e rs D e t a il


SIXTH SIXTH SENTENCESENTENCE::

The clerk also The clerk also prints an prints an invoice and invoice and shipping list shipping list for each for each order, which order, which are are forwarded to forwarded to Order Order Fulfillment.Fulfillment.

RESULTRESULT: ABC : ABC Records Records Order Order ProcessingProcessing

EE-1

R e c o rd C lu bM e mb e r

1


O R Clerk

EE-2


D -1 M e m b e r M a s t e rme m b e rd a t a

n o n -me mb e r o rd e ra n d a p p lic a t io n fo rm

2

Ver ify o rderitem data

O R Clerk

m e mb e ro rd e r

D -2 It e m M a s te rit e md a ta

3

Enter o rderinto D aily

O rdersO R Clerk

v e rifie dme mb e r

o rd e r

D -3 D a ily O rd e rs D e t a ilo rd e r

4

P rint invo ic eand

sh ipping lis tO R Clerk

o rd e rd a t a

EE-3

O rd e rF u lfillme n t

in v o ic e a n ds h ip p in g lis t

Rules for correctness of DFDRules for correctness of DFD Following questions are useful in evaluating DFD:-Following questions are useful in evaluating DFD:- Are there any unnamed components( data flows, Are there any unnamed components( data flows,

processes, stores, inputs, or outputs) in DFD?processes, stores, inputs, or outputs) in DFD? Are there any data stores that are input but never Are there any data stores that are input but never

referenced?referenced? Are there any processes that do not receive input?Are there any processes that do not receive input? Are there any processes that do not produce output?Are there any processes that do not produce output? Are there any processes that serve multiple Are there any processes that serve multiple

purposes? (if so, simply divide it)purposes? (if so, simply divide it)

(2) Creating a Control Flow (2) Creating a Control Flow ModelModel

Represents “Represents “eventsevents” and the processes that ” and the processes that manage eventsmanage events

An “event” is a Boolean condition that can An “event” is a Boolean condition that can be ascertained by:be ascertained by:

listing all sensors that are "read" by the listing all sensors that are "read" by the software.software.

listing all interrupt conditions.listing all interrupt conditions. listing all "switches" that are actuated listing all "switches" that are actuated

by an operator.by an operator. listing all data conditions.listing all data conditions.

(3) (3) The Control Specification The Control Specification (CSPEC)(CSPEC)

The CSPEC can be:The CSPEC can be:state diagram state diagram (sequential spec)(sequential spec)

state transition tablestate transition table

activation tablesactivation tables

combinatorial speccombinatorial spec

(4)(4) The Process Specification The Process Specification (PSPEC)(PSPEC)

PSPECPSPECnarrativenarrativepseudocode (PDL)pseudocode (PDL)equationsequationstablestablesdiagrams and/or chartsdiagrams and/or charts

bubblebubble

Design Process and Design Design Process and Design QualityQuality

the design must implement all of the explicit the design must implement all of the explicit requirementsrequirements contained in the analysis model, contained in the analysis model, and it must accommodate all of the implicit and it must accommodate all of the implicit requirements desired by the customer.requirements desired by the customer.

the design must be a readable, the design must be a readable, understandable guideunderstandable guide for those who generate for those who generate code and for those who test and subsequently code and for those who test and subsequently support the software.support the software.

the design should provide a complete picture the design should provide a complete picture of the softwareof the software, addressing the data, , addressing the data, functional, and behavioral domains from an functional, and behavioral domains from an implementation perspective.implementation perspective.

Quality GuidelinesQuality Guidelines A design should exhibit an architectureA design should exhibit an architecture that (1) that (1)

has been created using recognizable architectural has been created using recognizable architectural styles or patterns, (2) can be implemented in an styles or patterns, (2) can be implemented in an evolutionary fashionevolutionary fashion For smaller systems, design can sometimes be For smaller systems, design can sometimes be

developed linearly.developed linearly. A design should be modularA design should be modular; that is, the software ; that is, the software

should be logically partitioned into elements or should be logically partitioned into elements or subsystemssubsystems

A design should contain distinct representationsA design should contain distinct representations of data, architecture, interfaces, and components.of data, architecture, interfaces, and components.

A design should lead to data structures that are A design should lead to data structures that are appropriateappropriate for the classes to be implemented and for the classes to be implemented and are drawn from recognizable data patterns.are drawn from recognizable data patterns.

Guidelines Continues….Guidelines Continues…. A design should lead to components that exhibit A design should lead to components that exhibit

independent functional characteristicsindependent functional characteristics.. A design should lead to interfaces that reduce A design should lead to interfaces that reduce

the complexitythe complexity of connections between of connections between components and with the external environment.components and with the external environment.

A design should be derived using a repeatable A design should be derived using a repeatable methodmethod that is driven by information obtained that is driven by information obtained during software requirements analysis.during software requirements analysis.

A design should be represented using a notation A design should be represented using a notation that effectively communicates its meaningthat effectively communicates its meaning..

Quality AttributesQuality AttributesA set of software quality attributes represents a A set of software quality attributes represents a

target fortarget forall software designs. all software designs. FunctionalityFunctionality:- feature set, capabilities, security:- feature set, capabilities, security UsabilityUsability:- overall consistency, documentation:- overall consistency, documentation ReliabilityReliability:- frequency and severity of failure, :- frequency and severity of failure,

accuracyaccuracyof output results, ability to recover failureof output results, ability to recover failure PerformancePerformance:- processing speed, response time, :- processing speed, response time,

resource consumption, throughput and efficiencyresource consumption, throughput and efficiency SupportabilitySupportability:- extensibility, adaptability, ease in :- extensibility, adaptability, ease in installationinstallation

Design ConceptsDesign Concepts (Assignment- (Assignment-1)1)

Submission date:- Aug 12Submission date:- Aug 12 abstractionabstraction—data, procedure, control—data, procedure, control architecturearchitecture—the overall structure of the software—the overall structure of the software patternspatterns—”conveys the essence” of a proven design —”conveys the essence” of a proven design

solutionsolution modularitymodularity—compartmentalization of data and function—compartmentalization of data and function Information hidingInformation hiding—controlled interfaces—controlled interfaces Functional independenceFunctional independence—single-minded function and —single-minded function and

low couplinglow coupling refinementrefinement—elaboration of detail for all abstractions—elaboration of detail for all abstractions Refactoring—a reorganization technique that simplifies Refactoring—a reorganization technique that simplifies

the designthe design Design ClassesDesign Classes

Unit 4

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Transcript of Unit 4