2. Slide 3.2
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. Slide 3.3
Software Life-Cycle Models
Life-cycle model
The steps through which the product
progresses
– Requirements phase
– Specification phase
– Design phase
– Implementation phase
– Integration phase
– Maintenance phase
– Retirement
4. Slide 3.4
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. Slide 3.5
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. Slide 3.6
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. Slide 3.7
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. Slide 3.8
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. Slide 3.9
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. Slide 3.10
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
12. Slide 3.12
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. Slide 3.13
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. Slide 3.14
Evaluating XP
XP has had some successes
Good when requirements are vague or
changing
Too soon to evaluate XP
15. Slide 3.15
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. Slide 3.16
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. Slide 3.17
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. Slide 3.18
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. Slide 3.19
Full Spiral Model
Radial dimension: cumulative cost to date
Angular dimension: progress through the spiral
20. Slide 3.20
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. Slide 3.21
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)
23. Slide 3.23
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
