IT607

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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 ?

Financial Gateway (bank)
Reservation System
Traveler
IVR system
Travel Agent
System administrator
Reservation Clerk
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Quiz 0
Assume, you are analyzing an existing railway
reservation system for devising enhancements.
Answer the following questions with reference to
any railway reservation system you are familiar
with. Please write your assumptions clearly. i)
Who are the various kinds of users of the system?
What are their expectations of the system? ii)
Will a system administrator who manages the
system be a user? Justify your answer ? iii) List
as many functional requirements of the system as
possible ? iv) Write down five non-functional
requirements of the system ?
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Quiz 0 (contd.)
v) Write down any additional requirements you
would like to add to the system? (mention clearly
whether they are functional or non-functional
requirements)   vi) Suppose, the system under
study has no facility for making reservations
using SMS. The customer wants this feature 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 the
system? 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,
  and enquiry facilities.
• Above facilities offered online and telephonic
  are highly appreciated

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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 highly appreciated
• Wants to be notified of important events like
  introduction of new / seasonal trains.

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Users expectations Reservation Clerk

• Reservation Clerks expectations of the System
• Reservation, cancellation, adjustment, and
  enquiry facilities.
• 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 sales reports 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 to
  safeguard the integrity of the payment data.
• System should be using EDI or any other standard
  data interchange formats that the financial
  gateway understands.
• Note Most of the external systems expectations
  are interoperability requirements.

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Product requirements

• The reservation system product requirements
• High availability ( less MTBF )
• High throughput handle more number of
  transactions per second
• Reliability
• Scalability
• Security etc.

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External requirements

• External requirements include
• Interoperability requirements. Ex Syntax and
  semantics of the messages to be used to
  communicate with the external systems.
• Legislative requirements. Ex Personal
  information of a client 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
  customer requires from a system and the
  constraints under which it operates and is
  developed.
• The requirements are the descriptions of the
  system services and constraints that are
  generated during the requirements engineering
  process.
• Running example Indian Railway Reservation
  System.

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Users

• The stakeholders of the system, who interact
  with the system to accomplish their tasks.
• A user may be any entity that is interested in
  the services offered by the system.
• Eg Traveler, Travel Agent, Reservation Clerk,
  Financial Gateway, System Administrator etc.

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User Requirements

• Different users have different expectations of
  the system behavior, and all these combined
  together constitute the overall system
  requirements
• Ex -
• Traveler expects an easy to use online system for
  booking tickets.
• A reservation clerk expects a good user interface
  and response time for serving the customers
  efficiently.
• A payment gateway expects the communication with
  the system be very secure, 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
• Reservation at counter should be closed by 8 p.m.
  every day.
• 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 for constructing a solution
• Most of the changing requirements fall in to
  this category
• Ex- Some time later, Indian railway may decide
  to provide online reservation 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 a consequence of organizational policies and
  procedures.
• Ex Operational time in railway reservation time
• External Requirements requirements which arise
  from factors external 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 a requirement is implemented
  correctly or not
• Traceable requirements traceability is the
  ability to describe and follow the life of a
  requirement throughout the software development
  life cycle. This is a very useful feature used
  in change management.

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Requirement Elicitation techniques

• Traditional Techniques
• Group elicitation techniques
• Prototyping

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Requirement Elicitation techniques

• Traditional Techniques
• Use of questionnaires and surveys
• Interviewing stakeholders
• Analyzing existing systems and processes

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Requirement Elicitation techniques

• Group elicitation techniques
• A small group is formed, including some of the
  stakeholders also, to elicit requirements. This
  group brainstorms to define the requirements for
  the new system.
• This requirement gathering technique is very
  effective as the end users take active part in
  requirement definition.
• Group size should be reasonably small.
• Group composition at least one representative
  from every group of end-users should be present
  in the group. This eliminates any bias in
  defining requirements.

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Requirement Elicitation techniques

• Prototyping
• Used when there is a great deal of uncertainty
  about the requirements, or where early feedback
  from stakeholders is needed.
• 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
  development team
• 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 Specifications
• ex. finite state machines

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Problems with natural language

• Lack of Clarity precision is difficult
  without making the document difficult to read.
• Requirements Confusion functional and
  non-functional requirements tend to be mixed-up.
• Requirements Amalgamation several different
  requirements may be expressed together.
• Ambiguity the readers and writers of the
  requirement must interpret the same words in the
  same way. Natural language is ambiguous so this
  is very difficult.
• Lack of Modularization natural language
  structures are inadequate to structure system
  requirements.

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Structured Natural Language

• A predefined template is used for documenting
  the requirements. All the requirements are
  written in a standard way.
• 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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Structured Natural Language
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, train code 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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Structured Natural Language
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 user Requires Pre-condition required seats/berths are unreserved Post-condition required seats/berths are reserved and no more available for reservation. Side-effects None
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Analysis Models

• Use cases, Sequence Diagrams, Class Diagrams,
  Object Diagrams, Collaboration Diagrams etc.
• to be discussed in the next class