Requirements Analysis & Requirements Specification

1. Requirements Analysis&Requirements Specification Originally developed by Michael Madigan StorageTek Manager, PAL Engineering Software Engineering of Standalone Programs University of Colorado, Boulder

2. Requirements Engineering Requirements Engineering Requirements Elicitation Requirements Analysis Requirements Verification Requirements Specification Requirements Management

3. Requirements Analysis & Specification Definitions • Requirements Analysis • The process of studying and analyzing the customer and the user/stakeholder needs to arrive at a definition of software requirements.1 • Requirements Specification • A document that clearly and precisely* describes, each of the essential requirements of the software and the external interfaces. • (functions, performance, design constraint, and quality attributes) • Each requirement is defined in such a way that its achievement is capable of being objectively verified by a prescribed method; for example inspection, demonstration, analysis, or test.2

4. Types of Requirements • Functional requirements • Performance requirements • Speed, accuracy, frequency, throughput • External interface requirements • Design constraints • Requirements are usually about “what”, this is a “how”. • Quality attributes • i.e. reliability, portability, maintainability, supportability

5. What vs. How Dilemma3 User Needs WhatHow System Requirements WhatHow System Design WhatHow SoftwareRequirements WhatHow SoftwareDesign

6. Requirements vs. Design

7. Software Quality Attributes4 • Correctness • Reliability • Rating = 1 – (Num Errors/ Num LOC) • Can be allocated to subsystems • Efficiency • Integrity • Usability • Survivability • Maintainability • Verifiability • Flexibility • Portability • Reusability • Interoperability • Expandability

8. Analysis of Elicitation results helps to create a Vision Settle on which problem - Explain in the problem statement (2.2) Marketing group establishes positioning of the product (2.3) Stakeholder and User Summaries - User is a special case of stakeholder - Identify all stakeholders w.r.t. development: Name Represents Role - Identify all users w.r.t. system: Name Description Stakeholder

9. Stakeholder Profiles (3.5) Representative - who (name) is representing this stakeholder type. Description - brief description of the stakeholder type Type - Qualify s-h’s expertise, technical background, degree of sophistication Responsibilities - List s-h’s key responsibilities with regard to the system being developed - why a stakeholder? Success Criteria - How does the stakeholder define success? How rewarded? Involvement - involved in the project in what way? Requirements reviewer, system tester, ... Deliverables* - required by the stakeholder Comments/Issues - Problems that interfere w/ success, etc.

10. User Profiles (3.6) Representative - Who represents this user? (might be a stakeholder) Description - of the user type Type - qualify expertise, technical background, degree of sophistication Responsibilities - user’s key resp.’s w.r.t. system being developed Success Criteria - how this user defines success? rewarded? Involvement - How user involved in this project? what role? Deliverables - Are there any deliverables the user produces? For whom? Comments/Issues - Problems that interfere w/ success, etc. This includes trends that make the user’s job easier or harder

11. User Environment (3.4)-- working environment of target user Number of people involved in doing this now? Changing? How long is a task cycle now? Changing? Any unique environmental constraints: mobile, outdoors, in-flight, etc. Which system platforms are in use today? future? What other applications are in use? Need to integrate?

12. Key Stakeholder or User Needs (3.7) List key problems with existing solutions as perceived by the stakeholder or user. What are the reasons for this problem? How is it solved now? What solutions does the stakeholder want? What is relative importance of solving each problem? Alternatives and Competition (3.8)

13. Product Overview (4.)(at last!) 4.1 Product perspective (context) Put the product in perspective to other related products and the user’s environment. Independent? Component of a larger system? How do the subsystems interact with this? Known interfaces between them and this component? Block diagram

14. Product Overview (4.)(at last!) 4.2 Summary of Capabilities Customer Benefit Supporting Features 1. 2. 3. 4.

15. Product Overview (4.)(at last!) 4.3 Assumptions and dependencies What factors affect the features above? List assumptions that, if changed, ALTER this document 4.4 Cost and pricing -- not done by engineering 4.5 Licensing and installation -- different types of license enforcement will create more requirements for the development effort

16. Product Features (5.) What’s a feature? - high level capability necessary to deliver benefit to the user - externally desired service that typically requires inputs to achieve Level of detail must be general -- this is not the requirements spec for the developers. Provide the basis for product definition, scope management, and project management. Each will be expanded in the use-cases or other requirements Externally perceivable by users or external systems

17. What is not in theProduct Features Section? • Design • Constraints -- These go in section 6. • Design constraints • External constraints • Quality Ranges -- These go in section 7 • ranges for performance, robustness, fault tolerance, etc. that are not really features (specific capabilities, functions)

18. Precedence and Priority (8.) • Which features essential? • We will delay shipment in order to have these • We will postpone the feature in order to meet first-release goal

19. Other Product Requirements • These are requirements that are not features (functions) of the product • hardware platform requirements -- • system requirements -- supported host o.s.’s, peripherals, companion software • environmental requirements -- temperature, shock, humidity, radiation, usage conditions, resource availability, maintenance issues, type of error recovery • applicable standards -- legal, regulatory, communications

20. Documentation Requirements • What must be developed to support successful deployment? • User Manual? • Online Help? • Installation guide? Read Me file? • Labeling, packaging?

21. Vision Doc adds basis for SRS

22. Use Case Name Scope Level Primary Actor Stakeholders & interests Preconditions Success Guarantee (post-conditions) Basic Flow Alternate Flows (extensions) Error Flows Subflows Special requirements Technology & data variations list Frequency of occurrence Open Issues Use Case Internals -- Compare to example in Larman text (p. 68 ff.). Terms: 73-78

23. Fully Dressed Example: Process Sale, Larman text, p. 68 ff. Primary Actor: Cashier Stakeholders and Interests: - Cashier:Wants accurate, fast entry, and no payment errors, as cash drawer shortages are deducted from his/her salary. - Salesperson:Wants sales commissions updated. - Customer:Wants purchase and fast service with minimal effort. Wants proof of purchase to support returns. - Company:Wants to accurately record transactions and satisfy customer interests. Wants to ensure that Payment Authorization Service payment receivables are recorded. Wants some fault tolerance to allow sales capture even if server components are unavailable. Wants automatic and fast update of accounting and inventory.

24. Fully Dressed Example: Process Sale, Larman text, p. 68 ff. - continued - Government Tax Agencies: Want to collect tax from every sale. May be multiple agnecies such as national, state, and county. - Payment Authorization Service: Wants to receive digital authorization requests in the correct format and protocol. Wants to accurately account for their payables to the store. Preconditions:Cashier is identified and authenticated. Success Guarantee (Postconditions): Sale is saved. Tax is correctly calculated. Accounting and Inventory are updated. Commissions recorded. Receipt generated. Payment authorization approvals are recorded.

25. Main Success Scenario (of Basic Flow): 1. - 10. Extensions (Alternative Flows): *a. *b. 1a 2-4a 3a. 3b. 3c. 3-6a-c 4a 5a-c 6a 7a-f 9a-c Fully Dressed Example: Process Sale, Larman text, p. 68 ff. - continued

26. Fully Dressed Example: Process Sale, Larman text, p. 68 ff. – cont. Special Requirements: - Touch Screen UI on a large flat panel monitor. Text visible from 1 meter. - Credit auth. response within 30 seconds 90% of the time. ... Technology and Data Variations List: ... Frequency of Occurrence: Could be nearly continuous. Open Issues: - What are the tax law variations? - Explore the remote service recovery issue. - What customization is needed for different businesses?

27. Now what -- after development of use case(s) • Look for consistency, correctness, completeness • Most important for core requirements likely to be implemented soon • By translation to other formats • See Vision Document • State diagrams and tables • Event tables • Condition tables • Domain diagram (UML)

28. References • 1 “Requirements Analysis,” Richard Thayer, SMC 10/97 Version 2, 1997 • 2 “IEEE Guide for Software Requirements Specification,” IEEE 830-1998 • 3 “Software Requirements:Objects, Functions, and States”, Prentice Hall, 1993 • 4 Software Quality Measurement for Distributed Systems, RADC-TR-83-175