Chapter 3 Prescriptive Process Models Software Engineering A

Chapter 3 Prescriptive Process Models Software Engineering: A Practitioner’s Approach, 6 th edition by Roger S. Pressman 1

Software process model § Attempt to organize the software life cycle by § defining activities involved in software production § order of activities and their relationships § Goals of a software process standardization, predictability, productivity, high product quality, ability to plan time and budget requirements 2

Code&Fix The earliest approach § Write code § Fix it to eliminate any errors that have been detected, to enhance existing functionality, or to add new features § Source of difficulties and deficiencies impossible to predict impossible to manage 3

Models are needed § Symptoms of inadequacy: the software crisis scheduled time and cost exceeded user expectations not met poor quality § The size and economic value of software applications required appropriate "process models" 4

Process model goals (B. Boehm 1988) "determine the order of stages involved in software development and evolution, and to establish the transition criteria for progressing from one stage to the next. These include completion criteria for the current stage plus choice criteria and entrance criteria for the next stage. Thus a process model addresses the following software project questions: What shall we do next? How long shall we continue to do it? " 5

Process as a "black box" Quality? Uncertain / Incomplete requirement In the beginning 6

Problems § The assumption is that requirements can be fully understood prior to development § Interaction with the customer occurs only at the beginning (requirements) and end (after delivery) § Unfortunately the assumption almost never holds 7

Process as a "white box" 8

Advantages § Reduce risks by improving visibility § Allow project changes as the project progresses based on feedback from the customer 9

The main activities of software production § They must be performed independently of the model § The model simply affects the flow among activities 10

Prescriptive Models Prescriptive process models advocate an orderly approach to software engineering That leads to a few questions … § If prescriptive process models strive for structure and order, are they inappropriate for a software world that thrives on change? § Yet, if we reject traditional process models (and the order they imply) and replace them with something less structured, do we make it impossible to achieve coordination and coherence in software work? 11

The Waterfall Model 12

Waterfall Model Assumptions 1. The requirements are knowable in advance of implementation. 2. The requirements have no unresolved, high-risk implications e. g. , risks due to COTS choices, cost, schedule, performance, safety, security, user interfaces, organizational impacts 3. The nature of the requirements will not change very much During development; during evolution 4. The requirements are compatible with all the key system stakeholders’ expectations e. g. , users, customer, developers, maintainers, investors 5. The right architecture for implementing the requirements is well understood. 6. There is enough calendar time to proceed sequentially. 13

Process for Offshore? Analysis Design Construct System test Accept. test Deploy 14

The V Model §If we rely on testing alone, defects created first are detected last User Need system test plan System Requirements Testing software test plan Software Requirements Testing integration plan Software Integration Design Testing unit plan Software Unit Implementation Testing time Product Release 15

Incremental Models: Incremental 16

Incremental Models: RAD Model 17

Evolutionary Models: Prototyping 18

Risk Exposure 19

Unified Process Model A software process that is: use-case driven n architecture-centric n iterative and incremental n Closely aligned with the Unified Modeling Language (UML) 20

The Unified Process (UP) inception 21

UP Work Products inception 22

Lifecycle for Enterprise Unified Process inception 23

Synchronize-and Stabilize Model § Microsoft’s life-cycle model § Requirements analysis—interview potential customers § Draw up specifications § Divide project into 3 or 4 builds § Each build is carried out by small teams working in parallel 24

Synchronize-and Stabilize Model (contd) § At the end of the day—synchronize (test and debug) § At the end of the build—stabilize (freeze build) § Components always work together Get early insights into operation of product 25

Evolutionary Models: The Spiral 26

Spiral Model § Simplified form Waterfall model plus risk analysis § Precede each phase by Alternatives Risk analysis § Follow each phase by Evaluation Planning of next phase 27

Simplified Spiral Model § If risks cannot be resolved, project is immediate ly terminate d 28

Full Spiral Model § Radial dimension: cumulative cost to date § Angular dimension: progress through the spiral 29

Full Spiral Model (contd) 30

Analysis of Spiral Model § Strengths Easy to judge how much to test No distinction between development, maintenance § Weaknesses For large-scale software only For internal (in-house) software only 31

Object-Oriented Life-Cycle Models § Need for iteration within and between phases Fountain model Recursive/parallel life cycle Round-trip gestalt Unified software development process § All incorporate some form of Iteration Parallelism Incremental development § Danger CABTAB 32

Fountain Model § Features § Overlap (parallelism) § Arrows (iteration) § Smaller maintenance circle 33

Software Process Spectrum Crystal Clear DSDM XP SCRUM d. X lightweight ICONIX FDD middleweight EUP Crystal Violet OPEN RUP heavyweight 34

Conclusions § § Different life-cycle models Each with own strengths Each with own weaknesses Criteria for deciding on a model include The organization Its management Skills of the employees The nature of the product § Best suggestion “Mix-and-match” life-cycle model 35

Model Driven Architecture 36

What is MDA in essence? § Automated approach to translate high level design to low level implementation by means of separation of concerns § From high-level model to running application § Risk proportional to expectations! 37

Finding the “right” language Developer IDEs & 4 GL 3 GL Automation Abstraction Model Driven Architecture Assembler Computer Hardware 38

“You should use iterative development only on projects you want to succeed” Martin Fowler 39

Model Driven Architecture § Can you actually have incremental MDA? Or is it automated waterfall? § Need rigorous models § Need high quality requirements Capture requirements Understand requirements 40

MDA or Offshore? § Automation versus reduce cost of labor § Objectives Reduce required intelligence Increase repetition § Goal Reduce costs of development 41