Requirements Engineering

1. Requirements Engineering NupulKukreja, Barry Boehm 7th September 2012

2. Agenda • Part 1 • Defining Requirements Engineering (RE) • Why is RE important? • Vision, Context and relation to RE • Three Dimensions of RE • Generic RE Framework • Part 2 • Requirements Practice in 577 • System and Software Requirements Document • User Stories • Documenting Requirements in 577

3. Requirements Engineering • Specifications of what should be implemented or as a constraint of some kind on the system • Defined during the early stages of system and software development • Types: • General property of the system (e.g. response time) • Detailed behavioral description (step by step scenario) • Specific constraint (must communicate with Amazon’s web service) • Information about computation details (e.g. interest computation for loans/mortgages etc.,

4. RequirementsEngineering* • Engineering implies application of systematic and repeatable processes • A systems and software engineering process which covers all of the activities involved in discovering, documenting and maintaining a set of requirements for a computer-based system *http://en.wikipedia.org/wiki/Requirements_engineering

5. Requirements Engineering* A cooperative, iterative and incremental process which aims at ensuring that: • All relevant requirements are explicitly known and understood at the required level of detail • A sufficient agreement about the system requirements is achieved between the stakeholders involved • All requirements are documented and specified in compliance with the defined documentation/specification formats and rules *Requirements Engineering: Fundamentals, Principles & Techniques – Klaus Pohl

6. Why Is RE Important? • Flawed requirements a major cause of project failure – one of top ten failures in Standish CHAOS Reports • Fixing an error in later phases 10x more expensive • Incorrect requirements  Incorrect system leads to wasted costs • System maybe unreliable for practical use disrupting normal day-to-day operations • The primary vehicle for going from “vision” to “realization”

7. Understanding “Vision” • Requirements Engineering processes start with an aim tochange current reality • Vision: (a.k.a “system vision”) • Essence of desired change defined briefly and precisely • Describes overall goal(s) of the system • Usually associated with particular point in time of when the vision should be realized • Serves as a guide during development for all Success Critical Stakeholders (SCS) involved in the project

8. Understanding “Context” • Each system is embedded within a given context (a.k.a. “system context”) • Context: Part of the system environment relevant for: • Defining • Understanding & • Interpreting system requirements

9. Visualizing “Vision” and “Context” • Establish system vision within existing system context • Deal with parts of the real world that are relevant and their relation to the development context Vision defines focus

10. Requirements Engineering: “Three Dimensions” • Content: • Understanding of the system requirements attained • Agreement: • Level of agreement achieved between stakeholders about defined requirements • Documentation: • Documenting and specifying the requirements using different documentation and specification techniques

11. Visualizing The “Three Dimensions” Content Goal complete Agreement consolidated views vague individual views Documentation informal compliant with rules

12. Framework For RE System Context Validation Core Activities Management Requirements Artifacts

13. Framework For RE System Context Subject FacetMaintain information about subjects in the real world. (Subjects subsume objects) Usage Facet Desired workflows, usage goals, different user groups, interaction models, laws & standards etc., IT System FacetExisting hardware, software, communication networks, peripheral devices etc., Development FacetProcess guidelines and constraints, QA methods, maturity models, development environments etc.,

14. Framework For RE Core Activities Documentation Document & specify elicited requirements as per defined documentation and specification rules. Also capture rationale and other relevant information Negotation1.Detect conflicts and make them explicit 2. Resolve identified conflicts Elicitation

15. Framework For RE Elicitation Identifying Requirement SourcesStakeholders Existing Documentation Existing System(s) Developing new & innovative requirementsTypically not elicit-able and require collaborative and creative processes Elicit Existing Requirements Elicit already “known” requirements from relevant sources

16. Techniques For Elicitation • Interviews • Workshops • Focus Groups • Observation of stakeholders/users etc., • Questionnaires • Perspective-based reading Usually supported by “Assistance Techniques” • Brainstorming • Prototyping • Mind Mapping • KJ Analysis/Method • Elicitation Checklists

17. Framework For RE Requirements Artifacts (Documented Requirements) Goals Stakeholder intention with regard to the objectives, properties or use of the system Scenarios Positive/Negative, Misuse, Exploratory, Current-state/desired state, Main, alternative or exception Solution oriented requirementsData Model, Functional Model, Behavioral Model

18. Framework For RE • Validation of context consideration Check whether all relevant aspects in 4 contexts have been elicited, documented within the RE process • Validation of execution of activities Check adherence of activities to process, standards, guidelines etc. • Validation of requirement artifacts Check documented requirements w.r.t. content, documentation and agreements Validation

19. Validation Techniques • Inspections • Walkthroughs • Desk-checking (checking programs with pen-paper) • Prototyping Above are usually assisted by: • Validation checklists • Perspective-based reading • Verbalization of models • Creation of artifacts

20. Framework For RE • Observation of system context Identification and management of context changes • Management of RE activities Monitoring, controlling and adjustment of planned workflow of elicitation, documentation, negotiation and validation activities – standard project management • Management of requirements artifacts • Establishing traceability between different artifacts • Prioritizing requirements • Managing changes via change management processes Management

21. RE Framework == VBSE 4+1  • RE Framework advocated by Klaus Pohl is in essence isomorphic to VBSE’s 4+1 • VBSE brings value considerations to the foreground; RE Framework doesn’t seem to make it explicit • Each of the ‘steps’ of the RE framework is traceable in VBSE’s 4+1 structure  (and vice versa)

22. Part 2 Requirements Practices in 577ab

23. RE Framework and 577 System Context QMP Subject FacetMaintain information about subjects in the real world. (Subjects subsume objects) Usage Facet Desired workflows, usage goals, different user groups, interaction models, laws & standards etc., IT System FacetExisting hardware, software, communication networks, peripheral devices etc., Development FacetProcess guidelines and constraints, QA methods, maturity models, development environments etc., LCP SSAD OCD SSAD

24. RE Framework and 577 Core Activities Documentation Document & specify elicited requirements as per defined documentation and specification rules. Also capture rationale and other relevant information Elicitation Negotation1.Detect conflicts and make explicit 2. Resolve identified conflicts WinWin Sessions Winbook

25. RE Framework and 577 Elicitation Identifying Requirement SourcesStakeholders Existing Documentation Existing System(s) Elicit Existing Requirements Elicit already “known” requirements from relevant sources Developing new & innovative requirementsTypically not elicit-able and require collaborative and creative processes WinWin Sessions Result Chains On-site Visits

26. RE Framework and 577 Requirements Artifacts Goals Stakeholder intention with regard to the objectives, properties or use of the system Scenarios Positive/Negative, Misuse, Exploratory, Current-state/desired state, Main, alternative or exception Solution oriented requirementsData Model, Functional Model, Behavioral Model OCD Result Chains SSAD Winbook

27. RE Framework and 577 IIV & V Project Management (Winbook)Prioritization Lifecycle Planning Prototyping Validation Management Bugzilla Feasibility Analysis Change Management ARBs

28. Requirements Capturing in 577 • Previously captured in System and Software Requirements Document (SSRD) • Capability requirements (both nominal and off-nominal): i.e., the fundamental subject matter of the system, measured by concrete means like data values, decision-making logic and algorithms. • Level of Service Requirements (sometimes referred to as Non-functional requirements): i.e., the behavioral properties that the specified functions must have, such as performance, usability, etc. • Global constraints: requirements and constraints that apply to the system as a whole e.g.: Interface Requirements, Budget and Schedule Requirements, Implementation Requirements, and other Project Requirements • Evolution Requirements: not included in initial delivery, but need to be supported by the System’s Architecture • Priorities on how the system must be implemented : MoSCoW( Must Have, Should Have, Could Have, Want to Have) • Commitment: addressing WinWin agreements, policies, constraints

29. Main Kinds of Requirements • Product Requirements • Capability Requirements • local to system, specific system functionality • Level of Service Requirements • local to system, may affect many system requirements • System Interface Requirements • varies, affects groups system requirements • Project Requirements • global to project, affects overall system requirements • Evolutionary Requirements • varies, effects design and implementation

30. Example of Nominal Requirement

31. Examples of Levels of Service • Dependability • Reliability • Availability • Usability • Ease of learning • Ease of use • Performance • Maintainability • Portability • Inter-operability (or binary portability) • Reusability

32. Poor Examples of LOS • M: The system should be as fast as possible • R: The system should be available 24/ 7 (even if organization does not support activities beyond day time) • S: The system shall be implemented as per the standards laid out by USC • A: The system shall be available 100% of the time (for an unreliable network- based system)

33. SSRD in Practice Too much detail and too much to capture The true 3D view In 2D

34. Change Management & SSRD?

35. Along came a Story User Stories SSRD What we thought… What was actually intended…

36. The User Story – 3Cs A promissory note of intent Discussion & clarification of intent (a.k.a requirement) Acceptance Tests Card Conversation Confirmation Lightweight Ecstasy

37. User Stories • Written on small index cards • Usually of the form: As a <role>, I can <activity> so that <business value> Ex.: As a Consumer I want to be able to see my daily energy usage so that I can lower my energy costs and usage • Lacks details captured by traditional requirements specifications • Details conveyed primarily through conversations

38. INVEST-ing in User Stories Commonly used acronym in the Agile World to describe attributes of a good user story:

39. Theory-W STOP THIS MADNESS! Customer Dr. Boehm Think of requirements as stakeholder negotiated win conditions!! Developer As a team discuss what will make each of you “win” (a.k.a. win conditions) Reach a mutual consensus and move forward (WinWin Equilibrium) Identify any issues and come up with options to resolve them

40. Putting It All Together Winbook Theory - W Requirement Specifications User Stories Gmail Facebook

41. Winbook • A collaborative, social networking based tool for requirements brainstorming similar to facebook… • …with requirements organization using color-coded labels similar to Gmail… • …to collaboratively converge on software system requirements reaching win-win equilibrium (based on Theory-W)… • …by keeping it short and simple like XP’s user stories!

44. Requirements in 577 • Requirements are treated as “Win Conditions” • Win Conditions are captured in Winbook • Win Conditions subsume user stories: • Capability Requirements/Win Conditions can be conveniently phrased as user stories • Win Conditions are negotiated within Winbook itself • Win Conditions are linked to corresponding use-cases facilitating “downstream value traceability”

45. Challenges in RE • Things that can (and do) make life difficult • Missing Requirements • Ambiguous Requirements (major problem) • Changing Requirements (changes in technology, marketplace, political & legal changes, economic changes etc.,) • Non-identified Stakeholders • Location/Time differences and communication overhead • IKIWISI (I’ll know it when I’ll see it) • Implicit Assumptions

46. Key Takeaways • Requirements are very critical to the field of Software Engineering • Almost everything documented information is a form of requirement • No single artifact to rule them all – content usually split across various artifacts • Very cooperative and iterative • Assumptions/Conflicts must be made explicit and validated/resolved • SSRD is more commonly found in the wild • 577 uses Winbook for documenting ‘requirements’ making the process ‘fun and lightweight’

47. References • Requirements Engineering: Fundamentals, Principles and Techniques – Klaus Pohl • Agile Software Requirements – Dean Leffingwell • Exploring Requirements: Quality Before Design – Gause & Weinberg • User Stories Applied – Mike Cohn • Software Engineering Economics – Barry Boehm