Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 1	

Requirements engineering processes	

Prof Ian So...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 2	

Objectives	

•  To introduce the activities in r...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 3	

RE process perspectives	

Different views of req...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 4	

Perceptions of requirements engineering	

•  Req...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 5	

Goals of requirements engineering	

•  Specify a...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 6	

RE process interactions	

Requirements engineeri...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 7	

A staged model of a requirements
engineering pro...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 8	

A spiral view of the RE process	

Requirements
s...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 9	

Process variability	

•  The factors that lead t...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 10	

Process activities	

•  Requirements discovery	...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 11	

Problem understanding	

•  Understanding the pr...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 12	

Is the product...	

•  An information system?	
...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 13	

Is the process...	

•  Customer-driven?	

–  Cu...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 14	

Is the customer…	

•  Homogeneous?	

–  Need to...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 15	

Has the developer...	

•  A document culture?	
...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 16	

Is the deployment environment...	

•  An existi...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 17	

Why is RE hard to get right?	

•  The world is ...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 18	

Typical process problems	

•  Requirements elic...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 19	

Symptoms of RE process problems	

•  Product pr...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 20	

Requirements management	

The process of managi...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 21	

Requirements management	

•  Requirements manag...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 22	

Requirements change	

•  The priority of requir...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 23	

Requirements evolution
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 24	

Enduring and volatile requirements	

•  Endurin...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 25	

Requirements classification	

Requirement
Type
D...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 26	

Requirements management planning	

•  During th...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 27	

Requirements identification	

•  A scheme has to...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 28	

Change management
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 29	

Traceability	

•  Traceability is concerned wit...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 30	

Tool support	

•  Requirements storage	

–  Req...
Requirements Engineering Processes,York EngD Programme, 2010 	

Slide 31	

Key points	

•  A staged requirements engineeri...
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Requirements engineering processes

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Discussion of processes used in requirements engineering to derive requirements for complex systems

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Requirements engineering processes

  1. 1. Requirements Engineering Processes,York EngD Programme, 2010 Slide 1 Requirements engineering processes Prof Ian Sommerville
  2. 2. Requirements Engineering Processes,York EngD Programme, 2010 Slide 2 Objectives •  To introduce the activities in requirements engineering processes •  To discuss the reasons why there RE processes vary significantly from one organisation to another •  To introduce the activity of requirements management
  3. 3. Requirements Engineering Processes,York EngD Programme, 2010 Slide 3 RE process perspectives Different views of requirements engineering processes
  4. 4. Requirements Engineering Processes,York EngD Programme, 2010 Slide 4 Perceptions of requirements engineering •  Requirements engineering (RE) means different things to different people –  It’s about problem analysis, and –  It’s about solution specification, and –  It’s the baseline for design, and –  It’s what you do at the start of the life-cycle. •  RE is all of these things so, as a consequence, there cannot be a single, definitive RE process •  RE processes vary dramatically depending on the type of system being developed and the maturity of the organisation procuring the system
  5. 5. Requirements Engineering Processes,York EngD Programme, 2010 Slide 5 Goals of requirements engineering •  Specify a product that satisfies the stakeholders and constraints •  Specify how that satisfaction is to be verified •  Enable project planning and cost estimation •  Manage change •  Write a description of the requirements in a form that is suitable for the customer for the system and for the system developer
  6. 6. Requirements Engineering Processes,York EngD Programme, 2010 Slide 6 RE process interactions Requirements engineering System design System acquisition
  7. 7. Requirements Engineering Processes,York EngD Programme, 2010 Slide 7 A staged model of a requirements engineering process Feasibility study Requirements elicitation and analysis Requirements specification Requirements validation Feasibility report System models User and system requirements Requirements document
  8. 8. Requirements Engineering Processes,York EngD Programme, 2010 Slide 8 A spiral view of the RE process Requirements specification Requirements validation Requirements elicitation System requirements specification and modeling System req. elicitation User requirements specification User requirements elicitation Business requirements specification Prototyping Feasibility study Reviews System requirements document Start
  9. 9. Requirements Engineering Processes,York EngD Programme, 2010 Slide 9 Process variability •  The factors that lead to variability in requirements engineering processes
  10. 10. Requirements Engineering Processes,York EngD Programme, 2010 Slide 10 Process activities •  Requirements discovery –  Interacting with stakeholders to discover their requirements. Domain requirements are also discovered at this stage. •  Requirements classification and organisation –  Groups related requirements and organises them into coherent clusters. •  Prioritisation and negotiation –  Prioritising requirements and resolving requirements conflicts. •  Requirements documentation –  Requirements are documented and input into the next round of the spiral.
  11. 11. Requirements Engineering Processes,York EngD Programme, 2010 Slide 11 Problem understanding •  Understanding the problem when developing requirements for a system is not a simple technical issue. •  Requirements engineers have to understand –  The product –  The process –  The customer (s) –  The developer (s) of the software –  The deployment environment
  12. 12. Requirements Engineering Processes,York EngD Programme, 2010 Slide 12 Is the product... •  An information system? –  Understanding the organisational environment is crucial; –  The organisation may change radically; •  An embedded or hybrid system? –  Operational environment needs to be understood; –  Solution architecture fixed early and hard to change; –  Production problems tend to migrate to the software. •  A custom-built system or a software product –  Do customers for know what their requirements are? –  Who supplies the requirements for a software product?
  13. 13. Requirements Engineering Processes,York EngD Programme, 2010 Slide 13 Is the process... •  Customer-driven? –  Customer is principal stakeholder; –  Typically a document-driven process. •  Market-driven? –  Time-to-market is the dominant constraint; –  Developer is principal stakeholder; –  Driven by product vision for first release. Subsequent releases need to balance developer’s strategic goals and customers’ requirements.
  14. 14. Requirements Engineering Processes,York EngD Programme, 2010 Slide 14 Is the customer… •  Homogeneous? –  Need to understand their business and strategic objectives. •  Heterogeneous? –  Need to trade off conflicting requirements, This is the normal situation. •  Merely potential? –  Need a proxy to represent the actual customer
  15. 15. Requirements Engineering Processes,York EngD Programme, 2010 Slide 15 Has the developer... •  A document culture? –  Documentation may be an overhead for small start-ups - but a creeping requirement as product and customer base grows. •  A quality culture? –  RE ‘products’ perceived to have only an indirect relationship to software products; –  Classical view of quality conflicts with short development cycles. •  An agile culture? –  No experience of dealing with requirements documents but works on the basis of prototyping and rapid evolution
  16. 16. Requirements Engineering Processes,York EngD Programme, 2010 Slide 16 Is the deployment environment... •  An existing environment with established processes and equipment? –  How should the system integrate with the existing equipment? Will existing processes be resistant to change? •  Flexible and geared to change? –  Are the people in the environment used to change or will they resist the system? –  Is the management tradionally hierarchical? •  Disciplined? –  Do the people in the environment work according to a process or do they set their own tasks?
  17. 17. Requirements Engineering Processes,York EngD Programme, 2010 Slide 17 Why is RE hard to get right? •  The world is complex –  The problem is not always tractable to analysis. •  The world changes –  The problem will change … and the solution may change the problem. •  Resources are scarce –  RE is always tightly time- and money-bound; –  Required effort will exceed budget.
  18. 18. Requirements Engineering Processes,York EngD Programme, 2010 Slide 18 Typical process problems •  Requirements elicitation –  Failure to consider all important stakeholders and therefore critical requirements are not included in the system •  Requirements analysis –  Failure to carry out a detailed analysis of the requirements –  System and problem models become inconsistent •  Requirements validation –  Failure to identify requirements tests –  Insufficient validation of requirements •  Requirements management –  Failure of change control and management of requirements
  19. 19. Requirements Engineering Processes,York EngD Programme, 2010 Slide 19 Symptoms of RE process problems •  Product problems –  Customer dissatisfaction –  Delays in implementing changes to products –  Unused product features •  People problems –  System stakeholders feel excluded –  Meetings failing to reach agreement •  Schedule problems –  Requirements changes take a long time to negotiate –  Extensive rework causes schedule delays
  20. 20. Requirements Engineering Processes,York EngD Programme, 2010 Slide 20 Requirements management The process of managing changes to system requirements
  21. 21. Requirements Engineering Processes,York EngD Programme, 2010 Slide 21 Requirements management •  Requirements management is the process of managing changing requirements during the requirements engineering process and system development. •  Requirements are inevitably incomplete and inconsistent –  New requirements emerge during the process as business needs change and a better understanding of the system is developed; –  Different viewpoints have different requirements and these are often contradictory.
  22. 22. Requirements Engineering Processes,York EngD Programme, 2010 Slide 22 Requirements change •  The priority of requirements from different viewpoints changes during the development process. •  System customers may specify requirements from a business perspective that conflict with end-user requirements. •  The business and technical environment of the system changes during its development.
  23. 23. Requirements Engineering Processes,York EngD Programme, 2010 Slide 23 Requirements evolution
  24. 24. Requirements Engineering Processes,York EngD Programme, 2010 Slide 24 Enduring and volatile requirements •  Enduring requirements. Stable requirements derived from the core activity of the customer organisation. E.g. a hospital will always have doctors, nurses, etc. May be derived from domain models •  Volatile requirements. Requirements which change during development or when the system is in use. In a hospital, requirements derived from health-care policy
  25. 25. Requirements Engineering Processes,York EngD Programme, 2010 Slide 25 Requirements classification Requirement Type Description Mutable requirements Requirements that change because of changes to the environment in which the organisation is operating. For example, in hospital systems, the funding of patient care may change and thus require different treatment information to be collected. Emergent requirements Requirements that emerge as the customer's understanding of the system develops during the system development. The design process may reveal new emergent requirements. Consequential requirements Requirements that result from the introduction of the computer system. Introducing the computer system may change the organisations processes and open up new ways of working which generate new system requirements Compatibility requirements Requirements that depend on the particular systems or business processes within an organisation. As these change, the compatibility requirements on the commissioned or delivered system may also have to evolve.
  26. 26. Requirements Engineering Processes,York EngD Programme, 2010 Slide 26 Requirements management planning •  During the requirements engineering process, you have to plan: –  Requirements identification •  How requirements are individually identified; –  A change management process •  The process followed when analysing a requirements change; –  Traceability policies •  The amount of information about requirements relationships that is maintained; –  CASE tool support •  The tool support required to help manage requirements change;
  27. 27. Requirements Engineering Processes,York EngD Programme, 2010 Slide 27 Requirements identification •  A scheme has to be devised for requirements identification so that requirements can be unambiguously identified •  The most common scheme is a nested numbering scheme e.g. 1.2.3. However, such schemes are a problem –  The top level classification (the first number) has to be fixed in advance –  There are problems when requirements are changed •  Major problem is ensuring that stakeholders use the requirements identification scheme in a consistent way
  28. 28. Requirements Engineering Processes,York EngD Programme, 2010 Slide 28 Change management
  29. 29. Requirements Engineering Processes,York EngD Programme, 2010 Slide 29 Traceability •  Traceability is concerned with the relationships between requirements, their sources and the system design •  Source traceability –  Links from requirements to stakeholders who proposed these requirements; •  Requirements traceability –  Links between dependent requirements; •  Design traceability –  Links from the requirements to the design;
  30. 30. Requirements Engineering Processes,York EngD Programme, 2010 Slide 30 Tool support •  Requirements storage –  Requirements should be managed in a secure, managed data store. •  Change management –  The process of change management is a workflow process whose stages can be defined and information flow between these stages partially automated. •  Traceability management –  Automated retrieval of the links between requirements.
  31. 31. Requirements Engineering Processes,York EngD Programme, 2010 Slide 31 Key points •  A staged requirements engineering process includes a feasibility study, requirements elicitation and analysis, requirements specification and requirements management. •  Social and organisational factors influence system requirements, resulting in variations in RE processes •  Business changes inevitably lead to changing requirements. •  Requirements management includes planning and change management.
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