User Requirements Phase Drawn from Sommerville and S. Lauesen , Software Requirements, Styles and Techniques , Ad

1. User Requirements PhaseDrawn from Sommerville and S. Lauesen, Software Requirements, Styles and Techniques, Addisson Wesley, 2002

2. Overview • User requirements capture and analysis is an early phase of every lifecycle model. • Capture means finding out what the user wants … using different dialog techniques … and documenting this. • Analysismeans studying thedocumentedrequirements for errors and technical consequences

3. Terminology • Product: the system to be delivered • Inner domain: product + surrounding work area, immediate users, their activities, other systems • Outer domain: customers, “second-level users”, AKA business domain • Product I/O • Domain I/O • Product-level requirements • Domain-level requirements • Actor: human or external system that communicates with the product • Stakeholder: people who ensure the success of the project. (Not the same as actors, why?)

4. Terminology Outer or Business Domain Actors Domain I/O Platform Product I/O Other systems Product Inner Domain Stakeholders

5. Scale of Requirements(responsibility) Questions: 1: what can we actually take responsibility for? 2: what is the right level of requirement?

6. The Typical URD • Introduction: including business goals • Limits of the system: scope and interfaces • Data requirements: data model + dictionary • Product functional requirements: function lists, feature reqs, process descriptions • Quality requirements: non-functional Documentation standards: PSS-05, IEEE 830

7. Types of Requirements • Functional requirements: describe what the system does, in terms of input data, output date, error messages, etc. • E.g. a spreadsheet, a database, a word processor, 3D game, etc

8. Types of Requirements Non-Functional(AKA Quality) Requirements: • “everything else” • The product • The development process • The system environment • We can place these in a taxonomy (Sommerville) with a checklist function • See also: • McCall and Matsumoto (1980) • ISO 9126 • IEEE 830 (software requirements specifications)

9. Non-functional Product Organizational External Usability Reliability Portability legislative Efficiency delivery standards interoperability implementation speed memory ethical throughput privacy/ security safety commercial

10. Requirements Capture • An iterative dialog between • End-users Requirements Analysts Using a variety of tools and techniques

11. Why don’t we just ask the Customer? • Stakeholders may have difficulty expressing their needs, or may ask for a solution that doesn’t meet their needs. • Stakeholders can have conflicting demands • Users find it difficult to imagine new ways of doing things, or to imagine the consequences of what they ask for • A system that fulfills the requirements may not fulfill user expectations • Sometimes there are no users because a product is completely new • Demands and the environment change over time

12. Capture techniques A good analyst: • knows many techniques, • knows when to use them and when not, • Combines and modifies techniques according to specific needs.

13. Techniques • Stakeholder analysis (small scale, who, what, why, risks, costs, solutions?) • (Group) interview (recorded, taped, filmed) • Observation (see also ethnography / immersive studies) • Task demo (“here’s how I usually …”) • Document studies (company info) • Questionnaires (large scale, capture statistics & opinions, open/closed questions) • Brainstorm (unstructured – anything goes) • Focus groups (structured) • Domain workshops (business process) • Design workshops (interface ideas) • Prototyping (product-level reqs., design-level reqs.) • Pilot experiments (COTS?) • Similar companies/ Related products • Ask suppliers (they know their customers)

14. Example: Organizing a Focus Group 1. Invite participants: 6-18 people, all stakeholders represented, max 30% are suppliers 2. Open the meeting: present the topic, let people get to know each other and relax 3. Bad experiences: roundtable discussion of past experiences with similar products or work domains. Record issues on whiteboard. Record ideas on whiteboard. Facilitator makes sure no one dominates. Supplier staff are low key

15. Focus Group (continued) 4. Imagine the Future: Invite ideas, invite speculation. Ask: why/when do you want this? Record ideas. 5. List the issues: edit on the fly, regroup and organise, combine similar. Record issues. 6. Prioritize issues: Each stakeholder group picks top ten – but don’t prioritize within these to avoid conflict. 7. Review the lists: rountable comment, and close the meeting

16. Requirements Analysis and Validation • “Are we building the right product”? • i.e. will we build the product the customer truly wants to have? (at least at some point in time!) • Paradox: only the customer can determine this … but the customer is non-technical!

17. Requirements Analysis • Analysis involves several types of checks and tests that can be carried out: • Validity • Consistency • Completeness • Realism • Verifiability

18. Validity • Problem: User may have incorrectly defined a functional requirements. All requirements must be checked for functional correctness • Methods: • Rapid prototype • Paper model • Animation/simulation • Check existing/historic data • Test case generation • URD reviews • System User Manual

19. Consistency • Problem: User may state requirements that contradict each other (Common with many end-users!) • E.g. year + 1 > year year is a 2-digit number 99 + 1 = 00 > 99 contradiction! Simplified model of the Year 2000 Problem

20. Consistency • Methods: • If requirements are formal use constraint solvers and/or CASE tools for automatic check • Manual check, unclear, error prone, combinatorial explosion! • Note: problem may not be solved by prototyping

21. Completeness • Problem: user may have forgotten some requirements, leaving holes in the requirements document. These may possibly be solved arbitrarily … but possibly not! • Methods: • Rapid prototyping • URD reviews • Test case generation • Use cases analysis • Tables • Fault/ decision trees

22. Realism (Feasibility) • Problem: User may express requirements that or not technically feasible (e.g. performance) or violate some non-functional requirement (e.g. legislative) • Methods: • Prototyping • Mathematical model/simulation (e.gqueueing theory) • URD reviews • External advice (e.g. lawyers)

23. Verifiability • Problem: Users may state requirements which can never be checked/verified, • E.g. “user interface must be user friendly and easy to use” • Contractual disputes may emerge • Methods: • Test case generation esp. acceptance tests • Usability metrics

24. Numerical Quality Requirements

25. Usability = fit for use + ease of use The five (ease of) usability factors (Schneiderman 1998): • Ease of learning • Task efficiency • Ease of remembering • Subjective satisfaction • Understandability Some developers claim we cannot optimize all 5, if so … which to prioritize?

26. Usability Metrics

28. Security Requirements While other requirements support use-cases ... safety requirements prevent abuse-cases. Customer has certain assets to be protected againstthreats. We will examine security under risk management later …

29. Requirements Capture Languages • Requirements need to be recorded as precisely as possible, • Therefore technical requirements languages are useful • Large variety of these in many styles • Wefirstconsiderstyles:merits and demerits

30. Style: Natural Language + easily understood (esp. by end-user) + no technical training needed + very high-level/compact requirements • unclear/ ambiguous • debugging is difficult • no inherent structure • no tool support for validation (spell checker?)

31. Style: Structured Natural Language E.g. tables, decision trees, fault trees, data dictionaries + understood by end-user (sometimes) + small technical training + some structure (e.g. nouns, verbs, relations etc) + improve completeness issues • unclear/ ambiguous • lack of standards • little tool support

32. Style: Graphical Requirements Language e.g. UML, SDL, Petri Nets, etc + high-level/compact + quite or very precise + increasing tool support + often standardized / multiple vendors, courses, books, consultants • needs technical training • rarely understood by non-IT people and end-users

33. Style: Formal Specification Logic: e.g. OCL, JML, VDM, Z, B, temporal logic Ad-hoc: e.g. queuing theory, Markov chain + good tool support for validation problems + can be used to generate test cases, prove code correctness + extremely precise and accurate • Needs technical training • Poorly understood by end-users • Notation hard to read, overly detailed or low level

34. Data Modeling • Data models describe data inside and outside the product • Good for experts, maybe difficult for end-users • Early models can survive all the way to coding • Good for completeness/consistency checking Options • Class Diagram (OO analysis) • Entity-Relationship diagram (Database theory) • Data dictionary: terms and meanings • Data expression: format and legal values. Use regular expressions or DTDs.

35. Tables: a structured style • Advocated by David Parnas • Informal but structured style • Easily understood by end-users • Many formats, e.g. nested tables • Good for completeness and consistency check • Good for business rules

36. Requirement x. The product shall suggest the following discount rates if a customer asks for a discount.