Requirements Engineering A Roadmap

1. Requirements Engineering A Roadmap Jichuan Chang cjc@cs.cmu.edu • Based on • “RE roadmap” by Nuseibeh & Easterbrook • RE course materials by Steve Easterbrook http://www.cs.toronto.edu/~sme/CSC2106S/index.html

2. Outline • Foundations • What is RE? • Why important? • Inter-disciplinary aspects of RE • Basic Requirements Engineering activities • Directions and Discussion

3. Discussion • About requirements: • What and How? Environment and Machine • Is there always a bridge from the real-world to the “machine”? • Is formal specification suitable for all requirements? • About RE: • Is RE really important? Who can benefic from RE? • What is really used in practice? • Why so many methods/techniques? How to evaluate and choose? • What’s the process that integrates methods and activities? • RE tools? Traceability? • Future directions: • What’s the impact of imperfect requirements? • inconsistency? incomplete? evolving? • What’s the impact to other development activities? • What’s the impact of architectural decision to NFRs? • What’s the impact of requirement reuse?

4. What is RE? • What’s Requirement?[IEEE Std] • A condition or capability needed by a user to solve a problem or achieve an objective. The set of all requirements forms the basis for subsequent development of the system or system component. • What is RE? [Zave94] • Requirements Engineering is the branch of systems engineering concerned with real-world goals for, services provided by, and constraints on software systems. • Requirements Engineering is also concerned with the relationship of these factors to precise specifications of system behavior and to their evolution over time and across system families.

5. Importance of Requirements • Engineering Argument • A good solution can only be developed if the engineer has a solid understanding of the problem. • Economic Argument • Defects are cheaper to remove if are found earlier. • Empirical Argument • Failure to understand and manage requirements is the biggest single cause of cost and schedule over-runs. • Safety Argument • Safety-related software errors arise most often from inadequate or misunderstood requirements • ……

6. Research on RE • Early research: One epigram summarized all of RE. • Reqts. say what the system will do and not how it will do it. • A time-consuming, bureaucratic & contractual process? • 1990’s: A field of study of it own right • Two series of international meetings:RE and ICRE • International journal by Springer. • Late 1990’s: Grown up enough • Many additional smaller meetings and workshops • Emphasize the use of contextualized enquirytechniques • Model indicative & optative properties of the environment • Handle inconsistent and evolving specification • Future: increasingly recognized as a critical activity

7. RE Basics • Dimensions of RE • What vs. How • What does a web browser do? • ‘What’ refers to a system’s purpose • external to the system • A property of the application domain • ‘How’ refers to a system’s structure & behavior • internal to the system • A property of the machine domain • Foundations of RE – Multi-discipline • Systems Theory, Systems Engineering, Math & Logic, Computer Science, Social Sciences, Cognitive Sciences, Philosophy, AI

8. RE process • RE in software lifecycle • Initial phase • may also span the entire life cycle • Essential RE process • Understand the problem • elicitation • Formally describe the problem • specification, modeling • Attain agreement on the nature of problem • validation, conflict resolution, negotiation • requirements management - maintain the agreement! • Sequential or iterative/incremental • RE groundwork • Feasibility, risk, concept of operations • Decide the RE process, methods and techniques

9. Outline • Foundations • Basic Requirements Engineering activities • Eliciting Requirements • Modeling and Analyzing Requirements • Communicating Requirements • Agreeing Requirements • Evolving Requirements • RE Tool • Directions and Discussion

10. Source of Requirements: Customer-driven, Market-driven, Hybrid Affect the role of Requirements Things to elicit System boundaries Stakeholders & User Classes Viewpoints Goals and tasks Scenarios/Use cases Elicitation techniques Interviews, questionnaires, surveys, meetings Prototyping Ethnographic techniques Knowledge elicitation techniques Conversation Analysis Text Analysis Elicitation process: Inquiry cycle Use case analysis Eliciting Requirements Ethnographic: a branch of sociology dealing with nonspecialists' commonsense understanding of the structure and organization of society

11. Modeling Requirements • Why Modeling? • Modeling can guide elicitation • it help you ask the right questions? • Modeling can provide a measure of progress: • if we’ve filled in all the pieces of the model, are we done? • Modeling can help to uncover problems • Does inconsistency in the model reveal interesting things…? • conflicting or infeasible requirements; confusion over terminology, scope, etc; reveal disagreements between stakeholders • Modeling can help us check our understanding • Can we test that the model has the properties we expect? • Can we reason over the model to understand its consequences? • Can we animate the model to help us visualize/validate the requirements?

12. Modeling Enterprises Goals & objectives Organizational structure Processes and products Agents and work roles Modeling Functional Requirements Structural views Behavioral views Timing requirements Modeling Non-functional Requirements Product requirements Process requirements External requirements Modeling Techniques • Information modeling: • ERD • Organization modeling: • i*, SSM, ISAC • Goal modeling: • KAOS, CREWS • Structured Analysis: • SADT, SSADM, JSD • Object Oriented Analysis: • OOA, OOSE, OMT, UML • Formal Methods: • SCR, RSML, Z, Larch, VDM • Quality tradeoffs: • QFD, win-win • Specific NFRs: • Performance:Timed Petri nets • Usability: Task models • Reliability: Probabilistic MTTF

13. Communicating Reqts - SRS • How do we communicate the Requirements to others? • It is common practice to capture them in an SRS • Purpose • Communicates an understanding of the requirements • Contractual • Baseline for evaluating subsequent products • testing, V&V • Baseline for change control • Audience • Users, Purchasers • Requirements Analysts • Developers, Programmers • Testers • Project Managers

14. SRS for Procurement • An ‘SRS’ may be written by: • the procurer (a call for proposals) • Must be general enough to yield a good selection of bids • … and specific enough to exclude unreasonable bids • the bidders (a proposal to meet the CfP) • must be specific enough to demonstrate feasibility and competence • … and general enough to avoid over-commitment • the selected developer • reflects the developer’s understanding of the customers needs • forms the basis for evaluation of contractual performance • or an independent RE contractor • Choice over what point to compete the contract • Early (conceptual stage) • Late (detailed specification stage) • IEEE Standard recommends SRS jointly developed by procurer and developer

15. Importance: Verification & Validation Maintenance Assessing change requests Tracing design rationale Document access Process visibility Management change management risk management control of the development process Difficulties: Cost Delayed gratification Size and diversity Current Practice Focuses on baselined requirements Coverage links from requirements forward to designs, code, test cases, links back from designs, code, test cases to requirements links between requirements at different levels Tools (manual, syntactic) ?? Approaches: UID, hypertext linking Ability: Follow links Find missing links Measure overall traceability Reqts Traceability

16. Agreeing Requirements • Two key problems: validation & negotiation • Validation - What is “truth” and what is “knowable”? • Approaches (Based on philosophical assumptions): • assumes there is an objective problem that exists in the world • design your requirements models to be refutable • validation is always subjective and contextualised • Method in practice: • Inspections, Reviews and Walkthroughs • Prototyping: Throwaway or Evolve? • Negotiation - How to reconcile conflicting goals? • Requirements Negotiation • Competition • Third Party Resolution • Bidding and Bargaining

17. Evolving Requirements • Software evolves because requirements evolve … • How to manage incremental change to reqts models? • How can multiple models (specifications) be compared? • How to capture the rationale for each change? • Traditional change management • Add, modify, remove requirements during development • Baselines, Change Requests, Review Boards • Software Families • The product line approach • Viewpoints • Requirements model is a collection of viewpoints • as a framework for understanding requirements evolution • Viewpoints are instantiated from viewpoint templates • Viewpoints contain consistency rules (no central control) • Internal rule, External rule, Work plan

18. RE Tool examples • Requisite Pro • http://www.rational.com/ products/reqpro/ • Support Unified Process • Support use-case based, declarative, and mixed representation (document templates) • Support Requirements Traceability • Integrated with change mgmt, modeling, testing, metrics and project mgmt tools. • DOORS • http://www.telelogic.com/doors/ • Support Requirements Traceability • Inter-project linking, Multiple Views • Integration with MS Office and external communication tools • Cradle • http://www.threesl.com/

19. Outline • Foundations • Basic Requirements Engineering activities • Directions and Discussion

20. Future Research Directions • Trends in the 1990’s • Emphasize the use of contextualized enquirytechniques • Model indicative & optative properties of the environment • Handle inconsistent and evolving specification • Future Directions: • Modeling and analysis of problem domain, as opposed to the behavior of software. • Models for non-functional requirements (NFR). • Bridging the gap between contextual enquiry and formal specification techniques. • Impact of architectural choices on the prioritization and evolution of requirements. • Reuse of requirements models to facilitate the development of system families and COTS selection. • Multi-disciplinary training for requirements practitioners.

21. Discussion • About requirements: • What and How? Environment and Machine • Is there always a bridge from the real-world to the “machine”? • Is formal specification suitable for all requirements? • About RE: • Is RE really important? Who can benefic from RE? • What is really used in practice? • Why so many methods/techniques? How to evaluate and choose? • What’s the process that integrates methods and activities? • RE tools? Traceability? • Future directions: • What’s the impact of imperfect requirements? • inconsistency? incomplete? evolving? • What’s the impact to other development activities? • What’s the impact of architectural decision to NFRs? • What’s the impact of requirement reuse?