Software Process Models and Coherent Activities

1. Chapter 4 Software Processes

2. Software Processes • Coherent sets of activities for specifying, designing, implementing and testing software systems.

3. Objectives • To introduce software process models. • To describe a number of generic process models and when they may be used. • To outline lower-level process models for (1) requirements engineering, (2) software development, (3) testing, and (4) evolution. • To introduce CASE technology to support software process activities

4. Topics covered • Software process models • Process iteration • Software specification • Software design and implementation • Software verification & validation • Software evolution • Automated process support

5. The software process • A process is a structured set of activities required to develop a software system, e.g. • Specification • Design • Validation / Verification • Evolution • A process model is an abstract representation of a process. It presents a description of a process from some particular perspective • Models should be as simple as possible, but no simpler. – A. Einstein

6. The software process • A process is a structured set of activities required to develop a software system, e.g. • Specification • Design • Validation / Verification • Evolution • A process model is an abstract representation of a process. It presents a description of a process from some particular perspective • Models should be as simple as possible, but no simpler. – A. Einstein [struhk-cherd] –adjective; having and manifesting a clearly defined structure or organization.

7. Generic software process models • The Waterfall Model – separate and distinctphases of specification and development. Traditionally: not iterative. • Evolutionary Development – specification and development are interleaved. • Reuse-Based Development – e.g., component-based: the system is assembled from existing components. (And, at no additional cost: Incremental, eXtreme, and Spiral.)

8. Waterfall model (W. Royce)

9. Waterfall model problems • Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements. • Thus, this model is only appropriate when the requirements are well-understood (to begin with). --------------------------------------------- • In general, the drawback of the waterfall model is thedifficulty of accommodating change after the process is underway. Can we say anything good about the Waterfall model?

10. Evolutionary development • Exploratory Development*– objective is to work with customers and to evolve a final system from an initial outline specification. (Development starts with well-understood parts of system.)important theme in Agile Development • Throw-Away Prototyping – objective is to understand the system requirements. (Prototyping focuses on poorly understood requirements.) * also known as exploratory programming, or evolutionary prototyping (cont'd)

11. Evolutionary development customer trash (cont'd)

12. Evolutionary development • Potential problems • Lack of process visibility. (via documents: c.f. Waterfall model) • Final version/prototype is often poorly structured. • Special skills (e.g., in languages for rapid prototyping) may be required. – working effectively with people • Applicability • For small or medium-size interactive systems. • For parts of large systems (e.g., the user interface). • For short-lifetime systems. (In the case of exploratory development – why?)

13. Reuse-oriented development • Based on systematic (as opposed to serendipitous) reuse of existing software units. • Units may be: • Procedures or functions (common for past 40 years) • Components (“component-based development”) • Core elements of an application (“application family”) • Entire applications -- COTS (Commercial-off-the-shelf) systems • May also be based on use of design patterns. (cont'd)

14. Reuse-oriented development • Process stages: (following initial requirements specification) • Reusable software analysis (what’s available?) • Requirements modification – why? • System design with reuse • Development and integration • This approach is becoming more important, but experience is still limited. “Software Repositories” research was a major DoD thrust in the late 80’s. (cont'd)

15. Reuse-oriented development (what’s available?)

16. Process iteration • For large systems, requirements ALWAYS evolve in the course of a project. • Thus, process iteration is ALWAYS part of the process. • Iteration can be incorporated in any of the generic process models. (but not in keeping with spirit of Waterfall…) • Two other approaches that explicitly incorporate iteration: • Incremental delivery • Spiral development (Boehm)

17. Incremental delivery • Rather than deliver the system as a single unit, the development and delivery is broken down into increments, each of which incorporates part of the required functionality. • User requirements are prioritized and the highest priority requirements are included in early increments. • Once the development of an increment is started, its requirements are “frozen” while requirements for later increments can continue to evolve. (Compromise between Waterfall & Evolutionary development) (cont'd)

18. Incremental delivery (cont'd)

19. Incremental delivery advantages • Useful functionality is delivered with each increment, so customers derive value early. • Early increments act as a prototype to help elicit requirements for later increments. • Lower risk of overall project failure. • The highest priority system services tend to receive the most testing.(they're subject to more “validation” steps) (cont'd)

20. Potential problem with incremental delivery • Requirements may NOT be partitionable into stand-alone increments. (e.g., a compiler) (A generalization of incremental delivery, known as Incremental Software Development, is discussed in Chap. 17, Rapid Software Development.)

21. Extreme programming (Beck ’99) • Recent evolution of incremental approach based on • Development and delivery of very small increments of functionality • Significant customer involvement in process • Constant code improvement • Egoless, pair-wise programming • NOT document-oriented • Gaining acceptance in some small (and now medium sized) organizations. • Representative of the “Agile” development paradigm. www.agilealliance.org

22. Boehm’s spiral development • Process is represented as a spiral rather than a sequence of activities. • Each loop in the spiral represents a phase in the process. • No fixed phases such as specification or design – loops in the spiral are chosen depending on what is required. • Explicitly incorporates risk assessment and resolution throughout the process. (cont'd)

23. Spiral model of the software process

24. Spiral model quadrants • Objective Setting – specific objectives for the phase are identified. • Risk Assessment and Reduction – risks are assessed and activities put in place to reduce the key risks. • Development and Validation – a development model for the system is chosen which can be any of the generic models. • Planning – the project is reviewed and the next phase of the spiral is planned.

25. Models for (lower level) fundamental process activities • Software specification/requirements engineering (RE) • Software development (design and implementation) • Software verification and validation • Software evolution

26. Software specification / RE • The process of establishing what services are required and the constraints on the system’s operation and development. • Requirements Engineering (RE) process: • Feasibility (technical and otherwise) study • Requirements elicitation and analysis • Requirements specification (documentation) • Requirements validation (cont'd)

27. The requirements engineering process

28. Software design and implementation • The process of producing an executable system based on the specification • Software design – design a software structure that realizes the specification. • Implementation – translate this structure into an executable program. • The activities of specification, design, and implementation are closely related and may be interleaved.

29. Design process activities • “High-Level” design activities • Architectural design – subsystems and their relationships are identified • Abstract specification – of each sub-system’s services • Interface design – among sub-systems • “Low-Level” design activities • Component design – services allocated to different components and their interfaces are designed • Data structure design • Algorithm design

30. The software design process

31. Design methods • Systematic (canned) approaches to developing a software design. the cookbook approach… • The design is usually documented as a set of graphical models. • Possible models: • Data-flow model • Entity-relation-attribute model • Structural model • Object models

32. Programming and debugging • Translating a design into a program and removing errors from that program. • Programming is a “personal activity” – there is no generic programming process. • Programmers carry out some program testing to discover faults (“unit testing”), and remove faults in the debugging process. (Compare this model with Cleanroom SE.)

33. The debugging process

34. Software verification & validation • Verification and validation (V&V) determines whether or not a system (1) conforms to its specification and (2) meets the needs of the customer. • Involves inspection / review processes and (machine-based)testing. • Testing involves executing system elements with test cases that are derived from specifications and/or program logic.

35. Testing stages (topic 14) • Unit/Module testing - individual function/procedures are tested • (unit/module) Integration testing • Component testing - functionally related units/modules are tested together • (component) Integration testing • Sub-system/product testing - sub-systems or products are tested • (product/sub-system) Integration testing • System testing - testing of the system as a whole, including user acceptance test cf “traditional” (i.e., waterfall) model of testing…

36. Waterfall model (W. Royce)

37. Software evolution • Software is inherently flexible and subject to change. • As requirements change through changing business circumstances, the software that supports the business must also evolve and change. • The distinction between development and evolution is increasingly irrelevant as fewer and fewer systems are completely new. (cont'd)

38. System evolution e.g., change requests (cont'd)

39. The Rational Unified Process • A modern process model derived from the work on the UML and associated process. • Normally described from 3 perspectives • A dynamic perspective that shows phases over time; • A static perspective that shows process activities; • A practice perspective that suggests good practice. A hybrid process model that brings together elements from all of the generic process models…represents a new generation of generic processes (cont'd)

40. The Rational Unified Process • A modern process model derived from the work on the UML and associated process. • Normally described from 3 perspectives • A dynamic perspective that shows phases over time; • A static perspective that shows process activities; • A practice perspective that suggests good practice. A hybrid process model that brings together elements from all of the generic process models…represents a new generation of generic processes (cont'd)

41. RUP phase model cf Waterfall Model: RUP phases are more closely related to business rather than technical concerns. (cont'd)

42. RUP phases • Inception • Establish the business case for the system. • Elaboration • Develop an understanding of the problem domain and the system architecture. • Construction • System design, programming and testing. • Transition • Deploy the system in its operating environment. (cont'd)

43. The Rational Unified Process • A modern process model derived from the work on the UML and associated process. • Normally described from 3 perspectives • A dynamic perspective that shows phases over time; • A static perspective that shows process activities; • A practice perspective that suggests good practice. A hybrid process model that brings together elements from all of the generic process models…represents a new generation of generic processes (cont'd)

44. Static workflows(process activities)

45. The Rational Unified Process • A modern process model derived from the work on the UML and associated process. • Normally described from 3 perspectives • A dynamic perspective that shows phases over time; • A static perspective that shows process activities; • A practice perspective that suggests good practice. A hybrid process model that brings together elements from all of the generic process models…represents a new generation of generic processes (cont'd)

46. RUP good practice • Develop software iteratively • Manage requirements • Use component-based architectures • Visually model software (e.g., UML packages, sequence models, state machine models) • Verify software quality • Control changes to software

47. Automated process support (CASE) • Computer-aided software engineering (CASE) is software to support software development and evolution processes. • Activity automation (examples): • Graphical editors for system model development • Data dictionaries for name management • GUI builders for user interface construction • Debuggers to support program fault finding • Automated translators to generate new versions of a program (e.g., restructuring tools)

48. CASE technology • CASE technology has led to significant improvements in the software process, but not the order of magnitude improvements that were once predicted. • Software engineering involves design activity requiring creative thought – this is not readily automatable. • Software engineering is a team activity and, for large projects, much time is spent in team interactions. CASE technology does not support this well.

49. CASE classification • Classification helps us understand the different types of CASE tools / systems and their support for process activities • Functional perspective – tools are classified according to their specific function. • Process perspective – tools are classified according to process activities that are supported. • Integration perspective – CASE systems are classified according to their breadth of support for the software process.

50. TOOL TYPES: Planning tools Editing tools Change mgmt tools Configuration mgmt tools Prototyping tools Method-support tools Language-processing tools Program analysis tools Testing tools Debugging tools Documentation tools Reengineering tools EXAMPLES: PERT tools, estimation tools, spreadsheets Text editors, diagram editors, word processors Rqmts traceability tools, change control sys Version mgmt systems, system building tools V. high-level langs, user interface generators Design editors, data dicts, code generators Compilers, interpreters Cross ref generators, static/dynamic analyzers Test data generators, file comparators Interactive debugging systems Page layout programs, image editors Cross-ref systems, program restructuring systems Functional tool classification