Chapter 6: Software Requirements

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Chapter 6 Software Requirements

• Yonsei University
• 2nd Semester, 2009
• Sanghyun Park

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Contents

• Functional and non-functional requirements
• User requirements
• System requirements
• Software requirement document

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What Is A Requirement?

• The descriptions of the _______ and _________ of
  the system to be developed
• The process of finding out, analyzing,
  documenting, and checking these services and
  constraints is called __________ engineering

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Types Of Requirements (1/2)

• User requirements
• High-level abstract description of system
  services and constraints
• Written for _________
• System requirements
• Detailed description of what the system should do
• Written for senior technical staff and project
  ________
• Software specification
• Detailed software description which can serve as
  a basis for a design and implementation
• Written for _________

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Types Of Requirements (2/2)

• Functional requirements
• Statements of ________ the system should
  provide,how the system should react to
  particular inputs, andhow the system should
  behave in particular situations
• Non-functional requirements
• _________ on the services or functions offered by
  the system such as timing constraints,
  constraints on the development process,
  standards, etc.
• Domain requirements
• Requirements that come from the application
  _______ of the system and that reflect
  characteristics of that domain

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Functional Requirements

• Describe the functionality or services that the
  system is expected to provide
• Depend on the type of software, expected users,
  and type of system where the software is used
• Functional user requirements may be ____-level
  statements of what the system should do
• Functional system requirements should describe
  the system services in _____

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Examples Of Functional Requirements

• University library system
• The user shall be able to search either ___ of
  the initial set of databases or select a ______
  from it
• The system shall provide appropriate ______ for
  the user to read documents in the document store
• Every order shall be allocated a unique
  identifier (ORDER_ID) which the user shall be
  able to copy to the accounts permanent storage
  area

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Requirement Imprecision

• Problems arise when requirements are not _______
  stated
• __________ requirements may be interpreted in
  different ways by developers and users
• Consider the term appropriate viewers
• User intention special purpose viewer for each
  different document type
• Developer interpretation provide a text viewer
  that shows the contents of the document

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Completeness And Consistency

• In principle, the functional requirements should
  be both complete and consistent
• Completeness means that ___ services required by
  the user should be defined
• Consistency means that requirements should not
  have _____________ definitions
• For large and complex systems, it is _________
  impossible to achieve requirement consistency and
  completeness

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Non-Functional Requirements

• Define system _________ and __________
• Process requirements may also be specified
  __________ a particular CASE system, programming
  language, or development method
• Non-functional requirements may be more ________
  than functional requirementsif these are not
  met, the system is useless

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Non-Functional Requirement Types
Non-functionalrequirements
Organizationalrequirements
Productrequirements
Externalrequirements
Efficiencyrequirements
Reliabilityrequirements
Portabilityrequirements
Interoperabilityrequirements
Ethicalrequirements
Usabilityrequirements
Deliveryrequirements
Implementationrequirements
Standardsrequirements
Legislativerequirements
Performancerequirements
Spacerequirements
Privacyrequirements
Safetyrequirements
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Metric For SpecifyingNon-Functional Requirements

• Non-functional requirements are sometimes
  difficult to ______
• Ideally, non-functional requirements should be
  expressed ___________ using metrics

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Domain Requirements

• Derived from the application _______ and describe
  system characteristics and features that reflect
  the domain
• May be new functional requirements, constrain
  existing requirements, or define how particular
  computations must be carried out
• If domain requirements are not satisfied, the
  system may be ___________

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Domain Requirement Problems

• Understandability
• Requirements are expressed in the language of the
  ___________ domain
• This is often not understood by software
  engineers developing the system
• Implicitness
• Domain specialists understand the area so well
  that they do not think of making the domain
  requirements _______

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User Requirements

• High-level abstract description of system
  services and constraints written for customers
• Defined using ________ language, tables and
  diagrams

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Problems With Natural Language

• Lack of clarity
• _________ is difficult without making the
  document difficult to read
• Requirement confusion
• Functional and non-functional requirements tend
  to be _______
• Requirement amalgamation
• Several different requirements may be expressed
  ________

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Editor Grid Requirement

• 2.6 Grid facilities
• To assist in the positioning of entities on a
  diagram,the user may turn on a grid in either
  centimeters or inches, via an option on the
  control panel.Initially, the grid is off. The
  grid may be turned on and off at any time during
  an editing session and can be toggled between
  inches and centimeters at any time.A grid
  option will be provided on the reduce-to-fit view
  but the number of grid lines shown will be
  reduced to avoid filling the smaller diagram with
  grid lines.

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Requirement Problems

• The first sentence of editor grid requirement
  mixes three different kinds of requirements
• _________ functional requirement (the need for a
  grid)
• Non-functional requirement (detailed information
  on grid _____, centimeters or inches)
• Non-functional UI requirement(how the grid is
  switched on and off by the user)
• The user requirement should simply focus on the
  ____ facilities to be provided
• The _______ associated with the requirements is
  also important

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Editor Grid Requirement (Revised)

• 2.6 Grid facilitiesThe editor shall provide a
  grid facility where a matrix of horizontal and
  vertical lines provide a background to the editor
  window. This grid shall be a passive grid where
  the alignment of entities is the users
  responsibility.Rationale A grid helps the user
  to create a tidy diagram with well-spaced
  entities. Although an active grid, where entities
  snap-to grid lines can be useful, the
  positioning is imprecise. The user is the best
  person to decide where entities should be
  positioned.

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Guidelines ForWriting User Requirements

• Invent a _________ format and ensure that all
  requirement definitions adhere to that format
• Use language in a _________ wayuse shall for
  mandatory requirementsuse should for
  desirable requirements
• Use text __________ to identify key parts of the
  requirements
• Avoid use of _________ jargon

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System Requirements

• More ______ specifications of user requirements
• Serve as a basis for ________ the system
• In principle, the system requirements should
  state _____ the system should do and not ___ it
  should be implemented
• Natural language is often used to write system
  requirements however further ________ with
  natural language can arise

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Problems With NL Specification

• Ambiguity
• The readers and writers of the requirement must
  interpret the ____ words in the ____ wayNL is
  naturally ambiguous so this is very difficult
• Over-flexibility
• The ____ thing may be said in a number of
  ________ ways in the specification
• Lack of modularization
• NL structures are __________ to structure system
  requirements

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Alternatives To NL Specification

• Structured natural language
• Design description language
• Graphical notations
• Mathematical specifications

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Structured Natural Language

• The freedom of the requirement writer is limited
  by a predefined _________ for requirements
• The advantage is that the most of the
  ____________ of natural language is maintained
  but a degree of _________ is imposed on the
  specification
• Often best supported using a form-based approach

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Form-Based Specification

• Definition of the ______ or entity being
  specified
• Description of ______ and where they come from
• Description of ______ and where they go
• Indication of other entities required
• Pre and Post __________ (if appropriate)
• The _____ effects (if any) of the function

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Form-Based Specification Example
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Tabular Specification

• Used to supplement natural language
• Particularly useful when there are a number of
  possible _________ situations and we need to
  describe the ______ to be taken for each of these

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Tabular Specification Example
Action
Condition
Sugar level falling (r2 lt r1)Sugar level stable
(r2 r1) Sugar level increasing and rate
ofincrease decreasing ((r2-r1) lt (r1-r0)) Sugar
level increasing and rate ofincrease stable or
increasing ((r2-r1) (r1-r0))
CompDose 0CompDose 0 CompDose
0 CompDose round ((r2-r1)/4)If rounded
result 0 thenCompDose MinimumDose
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Graphical Models

• Most useful when we need to show how _____
  changes or where we need to describe a ________
  of actions
• Different graphical models are explained in
  Chapter 8

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Sequence Diagram Of ATM Withdrawal
ATM
Database
Card
Card number
Card OK
PIN request
PIN
Validate card
Option menu
ltltexceptiongtgt
invalid card
Withdraw request
Balance request
Balance
Amount request
Handle request
Amount
Debit (amount)
Debit response
ltltexceptiongtgt
insufficient cash
Card
Card removed
Completetransaction
Cash
Cash removed
Receipt
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Software Requirement Document

• The software requirement document is the official
  statement of what the system developers should
  implement
• It should include both the user requirements for
  a system and a detailed specification of the
  _______ requirements
• It is NOT a ______ document. As far as possible,
  it should set out WHAT the system should do
  rather than HOW it should do it

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Users Of A Requirement Document
Specify the requirements andread them to check
that theymeet their needs. Customersspecify
changes to therequirements.
Systemcustomers
Use the requirementdocuments to plan a bid
forthe system and to plan thesystem development
process.
Managers
Systemengineers
Use the requirements tounderstand what system
isto be developed.
System testengineers
Use the requirements todevelop validation tests
forthe system.
Systemmaintenanceengineers
Use the requirements tounderstand the system
andthe relationships between itsparts.
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IEEE Requirement Standard

• IEEE standard suggests the following structure
  for requirement documents
• Introduction
• General description
• Specific requirements
• Appendices
• Index

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Requirement Document Structure

• Preface
• Introduction
• Glossary
• User requirement definition
• System architecture
• System requirement specification
• System models
• System evolution
• Appendices
• Index