Transparency Masters for Software Engineering: A
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Transcript Transparency Masters for Software Engineering: A
Chapter 3
Prescriptive Process Models
Software Engineering: A Practitioner’s Approach, 6th edition
by Roger S. Pressman
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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
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
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"
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?"
Process as a "black box"
Informal
Requirements
Process
Product
Quality?
Uncertain /
Incomplete
requirement
In the beginning
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
Process as a "white box"
Informal
Requirements
Process
Product
feedback
Advantages
Reduce risks by improving visibility
Allow project changes as the project
progresses
based on feedback from the customer
The main activities of software
production
They must be performed independently
of the model
The model simply affects the flow
among activities
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?
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The Waterfall Model
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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.
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Process for Offshore?
Analysis
Design
Construct
System test
Accept. test
Deploy
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The V Model
If we rely on testing alone, defects
created first are detected last
User
Need
system test plan
System
System
Requirements
Testing
software test plan Software
Software
Requirements
Testing
integration plan
Software
Integration
Design
Testing
unit plan
Software
Unit
Implementation
Testing
time
Product
Release
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Incremental Models: Incremental
16
Incremental Models: RAD Model
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Evolutionary Models: Prototyping
18
Risk Exposure
19
Unified Process Model
A software process that is:
use-case driven
architecture-centric
iterative and incremental
Closely aligned with the
Unified Modeling Language (UML)
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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
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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
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Evolutionary Models: The Spiral
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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
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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
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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
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Fountain Model
Features
Overlap
(parallelism)
Arrows
(iteration)
Smaller
maintenance
circle
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Software Process Spectrum
Crystal Clear
DSDM
XP
SCRUM dX
lightweight
ICONIX
FDD
middleweight
EUP
Crystal Violet
OPEN
RUP
heavyweight
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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 & 4GL
3GL
Automation
Abstraction
Model Driven Architecture
Assembler
Computer Hardware
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“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
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