Sw Engg L4 Requirements Case Study

8/3/2019 Sw Engg L4 Requirements Case Study

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IT607 Software EngineeringRequirements Engineering

Kavi Arya

M. Mohan


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Objectives Introduce the concepts User and System Requirements

Describe functional and non-functional requirements

Explain how to document software requirements


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Railway reservation system Who are the users of this system ?

ReservationSystem

Financial Gateway(bank)

Traveler

Travel Agent

Reservation Clerk System administrator

IVR system


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Quiz 0

Assume, you are analyzing an existing railway reservationsystem for devising enhancements. Answer the followingquestions with reference to any railway reservation systemyou are familiar with. Please write your assumptions clearly.

i) Who are the various kinds of users of the system? Whatare their expectations of the system?

ii) Will a system administrator who manages the system bea user? Justify your answer ?

iii) List as many functional requirements of the system aspossible ?

iv) Write down five non-functional requirements of thesystem ?


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Quiz 0 (contd.)

v) Write down any additional requirements you would like toadd to the system? (mention clearly whether they arefunctional or non-functional requirements)

vi) Suppose, the system under study has no facility formaking reservations using SMS. The customer wants thisfeature to be implemented. Is this requirement functional?If no, can you think of a way of implementing this non-functional requirement in terms of any existing functional

requirements ?

vii) What process model would you adopt in building thesystem? Explain why and give two other models you would

not use, explaining why.


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Users expectations : Traveler

What are the Travelers expectations of the System ?

Expects reservation, cancellation, adjustment, andenquiry facilities.

Above facilities offered online and telephonic are highlyappreciated


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Users expectations : Travel Agent

Travel Agents expectations of the System

Bulk reservation, cancellation, adjustment facilities.

Enquiry facilities.

Above facilities offered online and telephonic are highlyappreciated

Wants to be notified of important events like introductionof new / seasonal trains.


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Users expectations : Reservation Clerk

Reservation Clerks expectations of the System

Reservation, cancellation, adjustment, and enquiryfacilities.

Season ticket issuing facility

Concession handling facility like handling concessions

given to senior citizens, Army personnel, students etc.

Report generation facility. Ex: for generating daily salesreports etc.


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Users expectations : System administrator

System administrators expectations of the System

A data backup facility

An error recovery facility

Adding, removing new trains to the system

Modifying train schedules and fares


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Users expectations : Financial Gateway

Financial gateways expectations of the System Communication with the system should be safe tosafeguard the integrity of the payment data.

System should be using EDI or any other standard datainterchange formats that the financial gatewayunderstands.

Note : Most of the external systems expectations are interoperabilityrequirements.


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Product requirementsThe reservation system product requirements

High availability ( less MTBF )

High throughput: handle more number of transactionsper second

Reliability

Scalability Security etc.


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External requirementsExternal requirements include:

Interoperability requirements. Ex: Syntax and semantics

of the messages to be used to communicate with theexternal systems.

Legislative requirements. Ex: Personal information of aclient should not be revealed to a third party without his

consent.


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Overall system requirements

User Requirements

Product Requirements

External Requirements


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Requirements Engineering

The process of establishing services that the customerrequires from a system and the constraints under which itoperates and is developed.

The requirements are the descriptions of the system

services and constraints that are generated during therequirements engineering process.

Running example : Indian Railway Reservation System.


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UsersThe stakeholders of the system, who interact with thesystem to accomplish their tasks.

A user may be any entity that is interested in theservices offered by the system.

Eg : Traveler, Travel Agent, Reservation Clerk, Financial Gateway, SystemAdministrator etc.


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User Requirements

Different users have different expectations of the systembehavior, and all these combined together constitute the

overall system requirements

Ex :-

1. Traveler expects an easy to use online system for booking tickets.

2. A reservation clerk expects a good user interface and response time forserving the customers efficiently.

3. A payment gateway expects the communication with the system be verysecure, to ensure the integrity of the payment data.


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Types of Requirements

Functional Requirements ( Application requirements )

Eg: Cancellation, Reservation, enquiry etc.

Non-Functional Requirements ( Quality Requirements )

Eg:

1. Reservation at counter should be closed by 8 p.m. every day.

2. Online reservations should be allowed till 11 p.m. etc.,


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Functional VS Non-functional requirements

Functional Requirements

Describes an interaction between the system and its environment

Functional requirements change less frequently

Non-functional Requirements

Describes a restriction or constraint that limit our choices forconstructing a solution

Most of the changing requirements fall in to this category

Ex:- Some time later, Indian railway may decide to provide onlinereservation facility round the clock.


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Classification of Non-functional requirements

Product Requirements: defines product characteristics

Ex: Execution speed, Reliability, Security, Scalability etc.

Organizational Requirements: requirements which are aconsequence of organizational policies and procedures.

Ex: Operational time in railway reservation time

External Requirements: requirements which arise from factorsexternal to the system.

Ex: interoperability requirements, legislative requirements etc.


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Characteristics of Requirements

Are they correct ?

Are they Consistent ?

Are they Complete ?

Are they Realistic ?

Are they verifiable ?

Are they traceable ?


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Characteristics of Requirements. .

Realistic Requirements : Are the requirements technically,financially, and operationally feasible ?

Verifiable requirements : Should be able to verify whether arequirement is implemented correctly or not

Traceable requirements : traceability is the ability to describeand follow the life of a requirement throughout the software

development life cycle. This is a very useful feature used in changemanagement.


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Requirement Elicitation techniques

Traditional Techniques

Group elicitation techniques

Prototyping


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Traditional Techniques

1. Use of questionnaires and surveys

2. Interviewing stakeholders

3. Analyzing existing systems and processes


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Group elicitation techniques

A small group is formed, including some of the stakeholders also,to elicit requirements. This group brainstorms to define therequirements for the new system.

This requirement gathering technique is very effective as the endusers take active part in requirement definition.

Group size should be reasonably small.

Group composition: at least one representative from every group ofend-users should be present in the group. This eliminates any bias indefining requirements.


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Prototyping

Used when there is a great deal of uncertainty about the

requirements, or where early feedback from stakeholders isneeded.

A prototype is:

Built rapidly from initial requirements

Analyzed to refine the requirements

New prototype is developed from these new requirements.

Process continues until requirements defined satisfactorily.


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Why document requirements ?

It will help clarify what you think

It is necessary to communicate with the users

It is necessary to communicate with the developmentteam

It could form a basis for a contractual relationship


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How to write it down ?

Natural Language

Structured Natural Language

Graphical Notations

ex. Use cases

Mathematical Specificationsex. finite state machines


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Problems with natural language

Lack of Clarity : precision is difficult without making thedocument difficult to read.

Requirements Confusion: functional and non-functionalrequirements tend to be mixed-up.

Requirements Amalgamation: several different requirementsmay be expressed together.

Ambiguity: the readers and writers of the requirement mustinterpret the same words in the same way. Natural language is

ambiguous so this is very difficult.

Lack of Modularization: natural language structures areinadequate to structure system requirements.


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A predefined template is used for documenting therequirements. All the requirements are written in a standardway.

Each template defines a unique function (reqmt) or entity.

Describes inputs and where they come from.

Describes outputs and where they go to.

Indicates other entities involved.

Pre and Post conditions (if appropriate).

The side effects (if any) of the function.


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XYZ software/SRS/1.2.4

Function:

Description:

Inputs:Source:

Outputs:

Destination:

Action:

Requires:

Pre-condition:

Post-condition:

Side-effects:


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Structured Natural Language contd

Indian railway reservation software/SRS/1.2.4

Function: reservation

Description: makes a reservation on behalf of a customer,

reservation clerk, or travel agent.

Inputs: journey date, source station, destination station, traincode etc.

Source: customer / reservation clerk / travel agent

Outputs: printed ticket or non-availability status message

Destination: customer / reservation clerk / travel agent


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Indian railway reservation software/SRS/1.2.4

Action: if seats/berths are available reserve them, otherwise send

a non-availability status message to the userRequires:

Pre-condition: required seats/berths are unreserved

Post-condition: required seats/berths are reserved and no moreavailable for reservation.

Side-effects: None


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Analysis Models

Use cases, Sequence Diagrams, Class Diagrams, ObjectDiagrams, Collaboration Diagrams etc.

to be discussed in the next class

Sw Engg L4 Requirements Case Study

Documents