Presentation is loading. Please wait.

Presentation is loading. Please wait.


Similar presentations

Presentation on theme: "CHAPTER 3 SOFTWARE LIFE-CYCLE MODELS."— Presentation transcript:


2 Overview Build-and-fix model Waterfall model Rapid prototyping model
Incremental model Extreme programming Synchronize-and-stabilize model Spiral model Object-oriented life-cycle models Comparison of life-cycle models

3 Software Life-Cycle Models
The steps through which the product progresses Requirements phase Specification phase Design phase Implementation phase Integration phase Maintenance phase Retirement

4 Build and Fix Model Problems
No specifications No design Totally unsatisfactory for any reasonable size software Need life-cycle model “Game plan” Phases Milestones

5 Waterfall Model The only widely-used model until the early 80’s
Characterized by Feedback loops Documentation-driven Each phase needs to be approved by SQA Advantages Enforced disciplined approach Documentation Maintenance easier Disadvantages Specifications not easily understood by clients Example stories (read textbook) Joe and Jane Johnson (house) Mark Marberry (suit)

6 Rapid Prototyping Model
Rapid prototype – a working model functionally equivalent to a subset of the product Determine what the client needs When developed, the client and users try using it When they are satisfied, the process moves to the next phase Linear model Specifications are drawn from the rapid prototype Feedback loops are not used “Rapid” is the key

7 Three Key Points Do not turn a rapid prototype into product
Rapid prototyping may replace specification phase—never the design phase Comparison: Waterfall model—try to get it right first time Rapid prototyping—frequent changes until the client is satisfied, then discard

8 Integrating Waterfall and Rapid Prototyping Models
Waterfall model Many successes Client needs may not be met Rapid prototyping model Some success but not really proven Has own problems Solution Rapid prototyping for requirements phase Waterfall for rest of life cycle

9 Incremental Model The product is designed, implemented, integrated and tested as a series of builds A build consists of code pieces from various modules interacting to provide a specific functionality Too few builds can lead to build-and-fix model Too many builds can lead to inefficient development

10 Incremental Model (contd)
Waterfall, rapid prototyping models Operational quality complete product at end Incremental model Operational quality portion of product within weeks Less traumatic Smaller capital outlay, rapid return on investment Needs open architecture—maintenance implications

11 Concurrent Incremental Model
More risky version—pieces may not fit CABTAB (code a bit and test a bit) and its dangers

12 Extreme Programming Somewhat controversial new approach based on the incremental model Development team determines stories (features client wants) Estimate duration and cost of each story Select stories for next build Each build is divided into tasks Test cases for task are drawn up first Pair programming Continuous integration of tasks

13 Unusual Features of XP Computers are put in center of a large room lined with cubicles Client representative is always present Cannot work overtime for 2 successive weeks No specialization All members of the team work on specification, design, coding and testing Refactoring No overall design The design is modified while the product is being developed

14 Evaluating XP XP has had some successes
Good when requirements are vague or changing Too soon to evaluate XP

15 Synchronize and Stabilize Model
Microsoft’s life-cycle model Also based on the incremental 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

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

17 Spiral Model Simplified Waterfall model plus risk analysis
Uses rapid prototypes Precede each phase by Alternatives Risk analysis Follow each phase by Evaluation Planning of next phase

18 Simplified Spiral Model
If risks cannot be resolved, project is immediately terminated Potential risks Timing constraints Lack of personnel Competence of team Dependency on hardware delivery

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

20 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

21 Object-Oriented Life-Cycle Models
Need for iteration within and between phases Fountain model [Henderson-Sellers and Edwards, 1990] Recursive/parallel life cycle [Berard, 1993] Unified software development process [Jacobson, Booch, and Rumbaugh, 1999] All incorporate some form of Iteration Parallelism Incremental development Danger CABTAB (undisciplined approach of s/w development, pg. 84)

22 Fountain Model Circles (phases) Overlap (parallelism)
Arrows (iteration) Smaller maintenance circle

23 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


Similar presentations

Ads by Google