1 / 18 CS 425/625 Software Engineering Requirements Engineering Processes Based on Chapter 6 of the textbook [Somm00] Ian Sommerville, Software Engineering, 6 th Ed., Addison-Wesley, 2000 and on the Ch6 PowerPoint presentation available at the book’s web-site: www.comp.lancs.ac.uk/computing/resources/IanS/SE6/Slides/ index.html September 22, 2003
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1 / 18 CS 425/625 Software Engineering Requirements Engineering Processes Based on Chapter 6 of the textbook [Somm00] Ian Sommerville, Software Engineering,
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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 theCh6 PowerPoint presentation available at the book’s web-site:www.comp.lancs.ac.uk/computing/resources/IanS/SE6/Slides/index.html
Introduction The requirements engineering process [Fig. 6.1, Somm00]
Feasibilitystudy
Requirementselicitation and
analysisRequirementsspecification
Requirementsvalidation
Feasibilityreport
Systemmodels
User and systemrequirements
Requirementsdocument
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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?
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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 system’s 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
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.Requirements Elicitation & Analysis….
The requirements elicitation & analysis process
[Fig. 6.2, Somm00]
Requirementsvalidation
Domainunderstanding
Prioritization
Requirementscollection
Conflictresolution
Classification
Requirementsdefinition andspecification
Processentry
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..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 system’s 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]
Validate user
Request PIN
Selectservice
Timeout
Return card
Invalid card
Return card
Stolen card
Retain card
Incorrect PIN
Re-enter PIN
Incorrect PIN
Return card
Card
PIN
Card present
Accountnumber
PIN
Accountnumber
Valid card
User OK
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….Requirements Elicitation & Analysis.
Use-cases [Fig. 6.12, Somm00]
Lending services
User administration
Supplier Catalog services
LibraryUser
LibraryStaff
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…..Requirements Elicitation & Analysis
Sequence diagram [Fig. 6.13, Somm00]
Bookshop:Supplier
Cataloguer:Library Staff
Item:Library Item
Books:Catalog
Acquire New
Catalog Item
Uncatalog Item
Dispose
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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
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.Requirements Validation.
Types of checks for requirements validation: Validity checks Consistency checks Completeness checks Reality/feasibility checks Verifiability
Requirements management planning involves decisions on: Identification of new requirements Change management process Traceability of requirements Tool support