Software Development Lifecycle Models

1. Software Development Lifecycle Models Fall 2009

2. Question: • We know that we have to do some things in order to get a software product completed: • Gather requirements • Design • Implement • Test • … • How do you order these activities so that you are most productive?

3. What is a lifecycle model? • Phase: activities to accomplish goals. • Lifecycle model: A model of the phases that start when the project is conceived and ends when the product is retired. • Depicts the relationships between the major milestones, reviews, deliverables. • Determines the order of activities.

4. A lifecycle model ... • Not a definition of the process an organization follows. • Does not provide rules or representations for development. • Is reference used to discuss the development of software.

5. Some Models • Code and fix • Waterfall • Prototyping • RAD • Incremental/evolutionary • Reusable components • Automated synthesis • Spiral • XP

6. 0. Code and Fix (aka “cowboy”) • Repeat • write code • fix it • Until code is good enough or resources exhausted

7. In class • What are the pros and cons of this approach? • (2 minutes)

8. 1. Waterfall (traditional) • First systematic approach, best studied. • Winston Royce • Some aerospace and government agencies mandate some form of this model. • Must be adapted to a particular situation or organization.

9. Waterfall Phases Feasibility Specify Requirements Design Implement Test Deliver Maintain

10. Feasibility Study • feasibility study

11. Requirements • requirements specification document (SRS) • states what qualities software must exhibit. • needs to be understandable, precise, complete, consistent, unambiguous, modifiable • preliminary user manual? • system test plan? • functional requirements • non-functional requirements

12. Design • design (preliminary and detailed) • decompose system into modules, selection of a software architecture • top-down, iterative

13. Code, Test, Deliver • coding and unit testing • create code (aka “programming”) • integration and system testing • this might be combined with the previous, done in incremental fashion • alpha testing • delivery • beta testing • acceptance testing

14. Maintain (evolution?) Corrective: (fix bugs) 12% = “emergency fixes” 9% = routine debugging Adaptive: (secondary changes) 17% = change data formats 6% = hardware changes Perfective (improve) 5% = improvements in documentation 4% = improvements in efficiency   42% = change user requirements Preventive (form of Perfective)

15. Advantages of Waterfall • Shows that software can be disciplined. • Forces attention on requirements and design before code. • Encourages planning. • Provides documents that can be used for testing. • Documents become part of legacy of system.

16. In Class • Clearly, waterfall has advantages over code and fix. • There are many criticisms of waterfall: what are they? • (3 minutes)

17. 2. Rapid Prototypes • Gomaa and Scott (early 80s) • Prototypes are throwaway. • Build prototype • User feedback drives correction of requirements • Toss the prototype • Build system in traditional way

18. In Class • How is this better than waterfall? • What are the costs?

19. 3. RAD • Rapid application development: • short development cycle based on components and 4GLs. • Used for • Modeling: business, data, and process • Application generation • Testing/installation

20. 3. RAD • Difficult to scale to large projects. • Works best when system can be modularized and is well understood (eg business apps). • Does not work well when technical risks are high, system cannot be modularized, or interfaces to other systems are an issue.

21. 4. Incremental/Evolutionary • Recognized as desirable by government • Incremental: • Design is totally laid out first • Functionality is provided in stages • Evolutionary: prototype evolves into final version  • Goal: get feedback earlier in process repeat give user something evaluate/measure adjust design and objectives

22. Incremental Development Iteration No. 1 2 3 867 868 Update SPMP1 Test whole Integrate Update Test documentation Test units Update source code Implement Design Update SDD2 Analyze requirements Update SRS3 1 Software Project Mangement Plan (chapter 2); 2 Software Design Document (chapter 5); 3 Software Requirements Specification (chapter 3); Adapted from Software Engineering: An Object-Oriented Perspective by Eric J. Braude (Wiley 2001), with permission.

23. In Class • What problems are we trying to fix with this method? • What pitfalls arise?

24. 5. Reusable software: • build it from parts. • this is the goal of the Ada project. • need to have parts, specs for parts, and tools for accessing them. • there are several methods of automating the lookup of parts. • specify as pre and post conditions.

25. 6. Automated Synthesis • Transformations: KIDS, SPECWARE, HATS • Start with a formal specification (mathematical) • successively refine this (formally) until code • may entail theorem proving • may entail computer assisted software engineering environment • Pre and post conditions • First order specifications, etc

26. 6. Automated Synthesis • Programmer can no longer fix the code directly. • Code is not result of coding, but of transforming. • Change the specs and the code changes. • Also correct by construction, proofs as programs

27. 7. Spiral • Barry Boehm (see IEEE Computer, vol 21, no 5, may 1988, pp61-72.) • meta-model • 4 stages in each cycle • identify objectives and alternatives • evaluate alternatives, identify risk, deal with risks • develop, verify, prototype, use any model • evaluate and plan next cycle •  starts with hypothesis that something can be improved • ends with product

28. Spiral Model Rapid prototype Specification Planning Design Implementation Integration • Objective setting: for each phase--identify constraints, risk, management plan • Risk Assessment and reduction • Develop and Validate • Planning: review project and decide whether to continue further in loop. Risk Analysis Verify Test

29. Spiral Model • Focus on eliminating errors early • Look at level of effort • Accommodates growth and change (evolution) • Restrictions • In-house development (not contracted) • Good for large-scale systems • Requires training in risk analysis and resolution

30. Driving Forces • waterfall: documentation driven • evolutionary: increment driven • transformational: specification driven • spiral: risk driven

31. USDP vs. Standard Terminology (Booch, Jacobson & Rumbaugh) Classification of iterations Individual iteration Inception Elaboration Construction Transition Iter. #k Prelim. iterations Iter. #1 Iter. #n Iter. #n+1 Iter. #m Iter. #m+1 .. … ….. Requirements Analysis USDP calls these “core workflows” (Classically called “phases”) Design Implementation Test

32. USDP vs. Standard Terminology 2 of 2 USDP Terminology Classical Terminology Requirements Analysis Requirements analysis Design Implementation Test Design Implementation Integration Test Adapted from Software Engineering: An Object-Oriented Perspective by Eric J. Braude (Wiley 2001), with permission.

33. Unified Process Matrix Jacobson et al: USDP Inception Elaboration Construction Transition Prelim. iterations Iter. #1 Iter. #n Iter. #n+1 Iter. #m Iter. #m+1 Iter. #k .. ….. ….. Requirements Analysis Amount of effort expended on the requirements phase during the first Construction iteration Design Implementation Test

34. Agile (1) moving quickly and lightly; (2) mentally quick; "an agile mind"; (3) Refers to the speed of operations within an organization and speed in responding to customers (reduced cycle times).

35. Agile Methods Agile is an iterative and incremental (evolutionary) approach to software development which [sic] is performed in a highly collaborative manner with "just enough" ceremony that produces high quality software which meets the changing needs of its stakeholders. • http://www.agilemodeling.com/essays/agileSoftwareDevelopment.htm

36. Values of Agile • Individuals and interactions over processes and tools • Working software over comprehensive documentation • Customer collaboration over contract negotiation • Responding to change over following a plan

37. Outline of Agile Methods • Minimize risk by developing software in short cycles • iterations • typically last one to four weeks • An iteration • like a miniature software project • includes planning, requirements analysis, design, coding, testing, and documentation. • At the end of each iteration, the team re-evaluates project priorities

38. Communications • Emphasize real time communication • face-to-face rather than written documents • All team members are co-located • programmers, testers, techwriters • managers • "customers" who define the product

39. In class • What are the advantages and disadvantages of having everyone at one site?

40. Software • Working software is the primary measure of progress • Very little written documentation relative to other methods • Criticism of agile methods: undisciplined • May or may not be true

41. History • Evolved in the mid 1990s • Reaction against "heavyweight" methods such as waterfall • Waterfall • Regimented and micromanaged • Bureaucratic, slow • Contradicts way SEs actually perform effective work • Agile is a return to practices seen early in software development • Is this good? Bad? • 2001 meeting at Snowbird adopted name “agile” over “lightweight”

42. History • Extreme Programming (XP) • Not first, but most popular • Established in 1966 by Kent Beck • Tried to save the Chrysler C3 project (but didn’t) • 1999 Elements of Extreme Programming

43. Different Agile Methods • Created prior to 2000 • Scrum • Crystal Clear (1986) • XP (1996) • Adaptive Software Development • Feature Driven Development • DSDM (1885)

44. Some of the principles behind the Agile Manifesto • Customer satisfaction by rapid (two weeks?), continuous delivery of useful software. • Working software is the principal measure of progress. • Late changes in requirements are welcomed. • Daily, face-to-face conversation is the best form of communication. • Projects are built around motivated individuals, who should be trusted. • Continuous attention to technical excellence and good design • Simplicity. • Self-organizing teams • Regular adaptation to changing circumstances

45. Adaptive vs Predictive Methods • Adaptive methods • focus on adapting quickly to changing realities • difficulty describing exactly what will happen in the future • The further away a date is, the more vague an adaptive method will be. • Team can report what tasks will be complete next week • Team can report what features will be worked on next month • Team cannot predict what features will be in the release 6 months out • Predictive methods • focus on planning the future in detail • difficulty changing direction • A predictive team can report exactly what features and tasks are planned for the entire length of the development process. • The plan is typically optimized for the original destination and changing direction can cause completed work to be thrown away and done over differently.

46. In class • List several characteristics of projects suitable for predictive methods and several characteristics of projects suitable for adaptive methods.

47. Agile Contrasted with Iterative • Iterative • Build releasable software in short time periods • Iterative time frames measured in months • Agile • Build releasable software in short time periods • Time frame in weeks • Time frame is strict

48. Agile Contrasted with Waterfall • Waterfall • Most predictive of methods: sequence of steps is highly planned • Document driven: progress is based on delivery of documents after each stage • Lengthy testing and integration phase at end of project • Delivers fully implemented software at the end of the project • Some agile teams use the waterfall model on a small scale, repeating the entire waterfall cycle in every iteration • Agile • Least predictive methods • Feature driven: progress based on delivery of features • Testing is part of feature development: no significant integration problems • Delivers fully developed features (but small subset of them) each development cycle

49. Agile Contrasted with Cowboy • "cowboy coding“ • Cowboy coding is the absence of a defined method: team members do whatever they feel is right • Success depends on heroics • Agile • Agile may be confused with cowboy • Agile teams follow defined (and often very disciplined and rigorous) processes

50. Suitability of Agile Methods • Organization must support negotiation • People must be trusted • Requires higher competence • Organizations must live with the decisions developers make • Organizations must support rapid communication • Suitable for projects with small teams, with fewer than 20 to 40 people.