requirements engineering by varma

7/30/2019 requirements engineering by varma

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By

Ravi Varma


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Requirements Engineering Requirements Engineering: is the process of establishing the

services that the customer requires from the system and theconstraints under which it is to be developed and operated

To create and maintain a system requirement documentWe have four high level RE sub process

1. Feasibility study: assessing whether the system is useful tobusiness

2. Elicitation and Analysis: Discovering requirements

3. Specification: converting the requirements into a standardform

4. Validation :check the requirements actually define thesystem that the customer wants


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Requirements Engineering Requirements Engineering Process


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SPIRAL REPRESENTATION OF REQUIREMENTS

ENGINEERINGProcess is represented as 3 stage activity.

1. Requirements Elicitation

2. Requirements Specification.

3. Requirements Validation.oActivities are organized as an iterative process around a

spiral.

o Early in the process, most effort will be spent on

Understanding high level business and the userrequirement.

o Later in the outer rings, more effort will be on systemrequirements engineering and system modeling.


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SPIRAL REPRESENTATION OF REQUIREMENTS

ENGINEERING

Requiremen ts

specificati on

Requirements

validation

Requirementselicitation

System requirements

specification andmodeling

System

requirementselicitation

User requirementsspecification

Userrequi rements

elicitation

Business requirementsspecification

Prototyping

Feasibility

study

Reviews

System requirements

document


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Feasibility study

A feasibility study decides whether or not the

proposed system is worthwhile.A short focused study that checks

If the system contributes to organisational objectives;

If the system can be engineered using current

technology and within budget; If the system can be integrated with other systems that

are used.


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Feasibility StudiesFeasibility study implementation

Based on information assessment, information collection

and report writing . Questions for people in the organization

-What if the system doesnt implemented?-What are current process problems?-How will proposed system help?-What will be the integration problems?-Is new technology needed? What skills?-What facilities must be supported by the

proposed system?


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Elicitation and Analysis Sometimes called requirements elicitation and

requirements discovery.

Involves technical staff working with customers to findout about the application domain the services that thesystem should provide and the systems operationalconstraints.

May involve end-users, managers, engineers involvedin maintenance, domain experts, trade unions, etc.These are called stakeholders


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Problems of requirements analysis Stakeholders dont know what they really want.

Stakeholders express requirements in their own terms.

Different stakeholders may have conflictingrequirements.

Organisational and political factors may influence thesystem requirements.

The requirements change during the analysis process.New stakeholders may emerge and the businessenvironment change.


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Requirements elicitation and

analysisThe Process Activities :

Requirements discovery: Interacting with stakeholders to discover their requirements. Domain

requirements are also discovered at this stage

Requirements classification and organisation Groups related requirements and organises them into coherent clusters.

Requirements prioritization and negotiation Prioritising requirements and resolving requirements conflicts.

Requirements documentation Requirements are documented and input into the next round of the spiral


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The requirements elicitation and

analysis process

Requirements

classification andorganisation

Requ irements

prioriti zatio n andnegotiation

Requ irements

documentation

Requirements

discovery


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Requirements DiscoveryViewpoints

Interviews

Scenarios Use-cases


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Requirements Discovery The process of gathering information about the

proposed and existing systems and distilling the userand system requirements from this information

Sources of information include documentation,system stakeholders and the specifications of similarsystems.

May involve end-users, managers, engineers involvedin maintenance, domain experts, trade unions, etc.These are called stakeholders.


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Requirements discoveryATM stakeholders Bank customers Representatives of other banks Bank managers Counter staff Database administrators Security managers Marketing department Hardware and software maintenance engineers Banking regulators


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ViewpointsViewpoints are a way of structuring the requirements

to represent the perspectives of different stakeholders.Stakeholders may be classified under differentviewpoints.

This multi-perspective analysis is important as there isno single correct way to analyse system requirements.


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Types of Viewpoints Interactor viewpoints

People or other systems that interact directly with the system. In anATM, the customers and the account database are interactor VPs.

Indirect viewpoints Stakeholders who do not use the system themselves but who

influence the requirements. In an ATM, management and securitystaff are indirect viewpoints.

Domain viewpoints Domain characteristics and constraints that influence the

requirements. In an ATM, an example would be standards for inter-bank communications


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LIBSYS viewpoint hierarchy

Article

providersFinance

Library

manager

Library

staffUsers

InteractorIndirect

All VPs

Classificationsystem

UI

standards

Do main

ExternalSta ffStudents CataloguersSystem

managers


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Interviewing In informal or formal interviewing , the RE team puts

questions to stakeholders about the system that theyuse and the system to be developed

Two types of interview.

closed interview s where a pre-defined set of questions

are answered Open interviews discuss a range of issues with

stakeholders for better understanding their needs.


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interviewing Normally a mix of closed and open-ended interviewing.

Interviews are good for getting an overall understanding ofwhat stakeholders do and how they might interact with the

system. Interviews are not good for understanding domain

requirements Requirements engineers cannot understand specific domain

terminology;

Some domain knowledge is so familiar that people find it hard toarticulate or think that it isnt worth articulating


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InterviewingEffective interviewers

Interviewers should be open-minded, willing to listento stakeholders and should not have pre-conceivedideas about the requirements.

They should prompt the interviewee with a question ora proposal and should not simply expect them to

respond to a question such as what do you want


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Scenarios

Scenarios are real-life examples of how a system can beused.

They should include

A description of the starting situation;

A description of the normal flow of events;

A description of what can go wrong; Information about other concurrent activities;

A description of the state when the scenario finishes


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Scenario for downloading article

in LIBSYSInitial assumption: The user has logged on to the LIBSYS system and has located the journal containing

the copy of the article.

Normal: T he user selects the article to be copied. He or she is t hen prompted by the syst em to ei ther

provide subscriber information for the journal or to indicate how they will pay for the article. Alternative

payment methods are by credit card or by quoting an organisat ional account number.

The user is then asked to fill in a copyright form that maintains details of the transaction and they then

submit this to t he LIBSYS system.

The copyright form is checked and, if OK, the PDF version of the art icle is downloaded to the LIBSYS

working area on the userscomputer and the user is informed that it is available. T he user is asked to select

a printer and a copy of the article is printed. If the article has been flagged as print-onlyit is deleted from

the users system once the user has confirmed that printing is complete.


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Scenario for downloading article

in LIBSYS

What can go wrong: T he user may fail to fill in the copyright form correctly. In t his case, the form should

be re-presented to the user for correction. If the resubmitted form is s till incorrect then the usersrequest

for the article is rejected.

The payment may be rejected by the system. The users request for the article is rejected.

The article download may fail. Retry until successful or the user terminates the session.

It may not be possible to print the article. If the article is not flagged as print-onlythen it is held in the

LIBSYS workspace. Otherwise, the article is deleted and the users account credited with the cost of the

article.

Other activities: Simultaneous downloads of other articles.

System state on completion: User is logged on. The downloaded article has been deleted from LIBSYS

workspace if it has been flagged as print-only.


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Another scenario for collecting

medical history


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Use cases Use cases are a requirements discovery technique that

were first introduced in the Objectory method.

They have now become a fundamental feature of theunified modeling language(UML).

Use-cases are a scenario based technique in the UMLwhich identify the actors in an interaction and which

describe the interaction itself


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Simple use case for printing article


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Use cases for the library system


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System interactions for article

printing Sequence diagram


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Next class Requirements validations

Requirements management

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requirements engineering by varma