Software Requirements elicitation and natural language specification

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Software Requirements elicitation and natural
language specification

• BY
• Touseef Tahir
• touseeftahir_at_ciitlahore.edu.pk

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Lecture Agenda

• What are software requirements
• Why software requirements are important
• Levels of software requirements
• Categories of software requirements
• Requirement elicitation techniques
• Requirement specification in natural language

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Background knowledge

• Software engineering
• Software engineering phases
• Software development life cycle

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System Definition

• A set or arrangements of elements that are
  organized to accomplish some predefined goal by
  processing information. And the goal may be a
  business function or to develop a product
  function.

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System Engineering

• Business Engineering

Product Engineering
System
Requirement Engineering
Ananalysis
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System Elements

• What are the system elements?
• Software
• Hardware
• People
• Database
• Documentation
• Procedures

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System Hierarchy

• World View (Domains)
• Domain View (Elements)
• Elements View( Sub elements)

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Software Engineering Phases

• Vision focus on why
• Definition focus on what
• Development focus on how
• Maintenance focus on change

Vision
Definition
Development
Maintenance
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Software Requirements - Definition

• Requirements are ... A specification of what
  should be implemented. They are descriptions of
  how the system should behave, or of a system
  property or attribute. They may be a constraint
  on the development process of the system. -
  Somerville 1997

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Requirements Parts (1)

• Requirements definition
• A statement in natural language plus diagrams of
  the services the system provides and its
  operational constraints. Written for customers
• Requirements specification
• A structured document setting out detailed
  descriptions of the system services. Written as a
  contract between client and contractor. For
  customers developers

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Requirement Engineering Phases

• Requirement Elicitation
• Requirement Analysis Negotiation
• Requirement Specification
• System Modeling
• Requirement Validation
• Requirement Management

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Role of Requirements
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Relationship of Software Requirements
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Why requirement engineering is important

• A survey on 8000 software projects
• Most of the projects failed due to incomplete
  requirements
• Cost to fix software errors

Requirements 1.0
Design 5.0
code 10.0
Testing 30.0
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Software Requirement in natural language
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Levels of software requirements

• Business requirements
• User/customer requirements
• Functional requirements
• Non-functional requirements

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An Example of Business Requirements

• An embedded system is to be developed for a kiosk
  (booth). This system will be sold to the retail
  stores and will be used by the store customers.

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An Example of Business Requirements

• For example, a business requirement to generate
  maximum revenue from the kiosk would imply the
  early implementation of features directly
  associated with selling more products or services
  to the customer, rather than glitzy features that
  appeal to only a subset of customers.

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Kinds of requirements (Spell Checker)

• BR user will be able to correct spelling errors
  in a document efficiently.
• Spell checker is included as a feature
• UR finding spelling errors in the document and
  decide whether to replace each misspelled word
  with the one chosen from a list of suggested
  words.
• FR
• find and highlight misspelled words.
• Display a dialog box with suggested replacements
• Making global replacements
• NFR It must be integrated into the existing
  word-processor which runs on windows platform.

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Levels of software requirements(Cont..)

• Functional Requirements
• Define the software functionalities the
  developers must build into the product.

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Levels of software Requirements(Cont..)

• Non-Functional Requirements
• Regulations
• Standards
• Quality attributes

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Non-Functional Requirements(Cont..)
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Levels of software Requirements(Cont..)
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Levels of software Requirements(Cont..)
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Categories of software requirements

• Bespoke requirements
• Market Driven Requirements

Particular customer
market segments
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Software Requirements Elicitation

• ...the process of discovering the requirements
  for a system by communication with stakeholders
  and through the observation of them in their
  domain
• (Tony Gorschek)

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Elicitation Techniques

• Interviews
• Getting to know the present (domain, problems)
  and ideas for future systems
• - Hard to see the goals and critical issues,
  subjective
• Group interviews
• Stimulate each other, complete each other.
• - Censorship, domination (some people may not
  get attention)

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Elicitation techniques (Cont)

• Observation
• Map current work, practices, processes
• - Critical issues seldom captured (e.g. you have
  to be observing when something goes wrong),
  usability issues seldom captured, time consuming

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Elicitation techniques (Cont)

• Task demonstrations
• Clarify what is done and how, current work.
• - Your presence and questions may influence the
  user, critical issues seldom captured, usability
  problems hard to capture

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Elicitation techniques (Cont)

• Questionnaires
• Gather information from many users (statistical
  indications, views, opinions)
• - Difficult to construct good questionnaires,
  questions often interpreted differently, hard to
  classify answers in open questions and closed
  questions may be too narrow

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Elicitation techniques (Cont)

• Brainstorming
• Many ideas (none are rejected)
• - Many ideas (have to be sorted and
  prioritized), hard to create a good atmosphere,
  hard to get everybody involved, small groups,
  time consuming

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Elicitation techniques (Cont)

• Use cases and Scenarios
• Concentration on the specific (rather than the
  general) which can give greater accuracy
• - Solution oriented (rather than problem
  oriented),can result in a premature design of the
  interface between the problem domain and the
  solution

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Elicitation techniques (Cont)

• Prototyping
• Visualization, stimulate ideas, usability
  centered, (can be combined with e.g. use cases)
• - Solution oriented (premature design), is it
  already done?!

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Software Requirement Specification

• Natural language specification
• RFC(Request For Comments) 2119
• Memorandum published by the Internet Engineering
  Task Force (IETF)

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Problems with Natural Languages - 1

• Requirement specification in natural language
  pose some problems which include
• Lack of clarity
• Requirements confusion
• Requirements amalgamation

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Software requirement properties

• Complete
• Feasible
• Unambiguous
• Verifiable
• prioritized
• Traceable
• Consistent
• Not design
• Not combined
• Correct

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Complete

• Requirement
• The system shall play the sound alarm when the
  door is opened.
• The system shall play the sound C\alarm.wav
  once, at the highest volume setting in the main
  speaker for the building X when the door Y opens.

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complete(Cont..)

• Requirement (Amalgamation)
• When a user has entered the building, this shall
  be registered in the entry log and the users
  computer shall be booted.
• When a user has entered the building, this
• shall be registered in the entry log.
• When a user has entered the building, the
• users computer shall be booted.
• The system shall register in the entry log
• when a user has entered the building.

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Feasible

• Implementable with current technical support
• Reality check while requirement elicitation

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Prioritization

• Assign an implementation priority
• Releases and software versions
• Microsoft word and notepad
• Methods of prioritization
• E-g 100 dollar method

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Verifiable

• Requirement
• The system shall respond quickly to user
  interaction.
• The system shall respond to user interaction
  within maximum 2 seconds, minimum 0.2 seconds,
  average 1 second (with a CPU load of 0.5).

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verifiable(Cont..)

• Requirement
• R11 When a user enters a correct code,
• the door shall open.
• When a user enters the code associated with
  him/her on keypad K2 the door D2 shall unlock and
  remain unlocked for 30 seconds.

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Traceable

• Backward-traceability Links requirements to their
  sources in other documents or people
• Forward-traceability Links requirements to the
  design and implementation components

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Consistent

• No conflict
• Example
• System must monitor all temperatures in a
  chemical reactor.
• System should only monitor and log temperatures
  below -200 C and above 4000 C.

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unambiguous

• Any two reader understand the requirement in same
  way.
• Example
• words such as "always," "never," "all, "or
  "every.
• Incomplete lists ending with "etc.," "and/or,"
  and "TBD.
• Vague words and phrases such as "generally,"
  "normally," "to the greatest extent," and "where
  practicable."

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References

• Software requirements objects and states by
  Justice Gul M.LIB.
• Software engineering (7th edition)by Sommerville
• Human aspects of software engineering by James E.
  Tomayko and Orit hazzan
• Introduction to software engineering by ronald
  J.Leach
• Software engineering theory and practice(2nd
  edition) by Shari Lawrence Pfleeger
• Requirements engineering processes and techniques
  by Gerald kotonya and Ian sommerville

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Assignment

• Assignment 1
• Make the group of five members and conduct the
  interview of a Head librarian. I will act as a
  head librarian and you will have to ask me the
  questions in order to know the problems.
• During a meeting with a customer (me) you
  shall acquire information about which system the
  customer wants, and what requirements that the
  customer poses on this system. You shall plan the
  customer meeting and prepare how you intend to
  get the required information from the customer.
  You shall conduct the meeting in a professional
  manner. You shall bring a printed paper to the
  meeting where the names and rollno of all
  participants are listed.
•  
• Assignment 2
• Make the observations about the working of
  manual library system. Identify different
  stakeholders and different scenarios of working.

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Assignment

• Write the requirements (in natural language) for
  system described.
• You are designing the software for a railway
  crossing. A sensor on the rails detects when a
  train is arriving and lowers the bars over the
  road. The bars remains lowered until another
  sensor detects that the train has passed or until
  a signal from the Railway Control Centre (RCC) is
  received. If the sensors malfunction, or if the
  connection to the RCC is lost, the bars are
  lowered and shall remain lowered until everything
  is working again and they are reset from the RCC.
  While the bar is being lowered or raised and
  while the bar is in its lowered position, lights
  will flash and a bell will ring

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Questions ?
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• Thank you