CS 425/625 Software Engineering Requirements Engineering Processes

1
CS 425/625 Software Engineering Requirements
Engineering Processes

• Based on Chapter 6 of the textbook Somm00 Ian
  Sommerville,
• Software Engineering, 6th Ed., Addison-Wesley,
  2000 and on the
• Ch6 PowerPoint presentation available at the
  books web-site
• www.comp.lancs.ac.uk/computing/resources/IanS/SE6/
  Slides/index.html
• September 22, 2003

2
Outline

• Introduction
• Feasibility Studies
• Requirements Elicitation and Analysis
• Requirements Validation
• Requirements Management

3
Introduction

• The requirements engineering process Fig. 6.1,
  Somm00

4
Feasibility Studies

• The input of a feasibility study is an outline
  description of the system
• The output is a report which recommends or not
  continuing the development process
• Activities
• Information collection
• Information assessment
• Report writing
• Questions asked during feasibility studies
• What contribution brings the new system to the
  organization?
• Can the system be built given its specific
  constraints?
• Can the system be integrated with already
  existing systems in the organization?

5
Requirements Elicitation Analysis

• Involves work with costumers and end-users to
  define the services and constraints of the system
• Stakeholders people who have direct or indirect
  influence on the way the systems requirements
  are shaped
• Challenges of requirements elicitation and
  analysis
• Stakeholders not clear about what they want
• Domain knowledge implicitly assumed
• Various ways of expressing requirements
• Political considerations involved
• Dynamic business and economic environment

6
.Requirements Elicitation Analysis.

• The requirements elicitation analysis process
• Fig. 6.2, Somm00

7
..Requirements Elicitation Analysis

• Three techniques for requirements elicitation and
  analysis
• Viewpoint-oriented elicitation various
  stakeholders points of view are taken into
  consideration (section 6.2.1 in Somm00)
• Scenario-based elicitation and analysis using
  concrete sections of operations the details of
  the systems requirements emerge
• Ethnography technique that focuses on
  understanding social and organizational
  requirements (section 6. 2.3 in Somm00)

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Requirements Elicitation Analysis..

• Event scenarios Fig. 6.10, SE-6

9
.Requirements Elicitation Analysis.

• Use-cases Fig. 6.12, Somm00

10
..Requirements Elicitation Analysis

• Sequence diagram Fig. 6.13, Somm00

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Requirements Validation..

• Requirements validation has the goal of ensuring
  that the system requirements do represent in fact
  what the user wants
• It is a form of requirements analysis which works
  with a complete set of requirements
• Very important activity since discovering
  problems with requirements at this stage saves a
  significant amount of money

12
.Requirements Validation.

• Types of checks for requirements validation
• Validity checks
• Consistency checks
• Completeness checks
• Reality/feasibility checks
• Verifiability
• Techniques for requirements validation
• Reviews
• Prototyping
• Test-case generation
• Automated consistency analysis

13
..Requirements Validation

• Automated consistency analysis of requirements
  Fig. 6.15, Somm00

14
Requirements Management.

• Requirements management is necessary because new
  requirements tend to emerge continuously. Its
  goal is to understand and control new
  requirements
• Reasons for new requirements
• Large systems have many users, with distinct sets
  of requirements, preferences, and priorities
• Differences between the views of customers (who
  pay for the system) and end-users (who actually
  work with the system)
• The systems environment evolves continuously

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.Requirements Management

• Requirements from an evolution standpoint
• Enduring requirements
• Volatile requirements
• Mutable
• Emergent
• Consequential
• Compatibility requirements
• Requirements management planning involves
  decisions on
• Identification of new requirements
• Change management process
• Traceability of requirements
• Tool support

16
..Requirements Management..

• Requirements Evolution Fig. 6.16, Somm00

17
Requirements Management.

• Traceability Matrix Fig. 6.18, Somm00

18
.Requirements Management

• Change management Fig. 6.19, SE-6