Software Engineering Spring 2002-2003 (C) Vasude va Varma Class 03 - 1 of 32 CS3600: Software Engineering: Process and Product* *Most of the Content drawn from Pressman Vasudeva Varma [email protected]Spring 2002 International Institute of Information Technology, Hyderabad
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Software Engineering Spring 2002-2003 (C) Vasudeva Varma Class 03 - 1 of 32
Software Engineering Spring 2002-2003 (C) Vasudeva Varma Class 03 - 2 of 32
Quick Review – Last week• Studied the definitions of SE• Discussed SDLC – Different phases• Discussed Fred Brooks’ work on SE
This week… We shall• Discuss Product and Process concepts• Look at various software Process models• Discuss CMM and PSP (Friday)
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What is Software Engineering?
• A modeling activity
• A problem-solving activity
• A knowledge acquisition activity
• A rationale-driven activity
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What Causes SW Projects to Fail?
• Unrealistic plans, based on optimistic estimates
• Ineffective tracking of performance
• Volatile requirements
• Risks
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But, Why do We Let it Happen?
• People tend to be risk averse when there is potential of loss
• People are unduly optimistic in their plans and forecasts
• People prefer to use intuitive judgment rather than quantitative models
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Controlling Human Nature
• Documenting the way work is performed • Provide guidance and quantifiable criteria
where possible• Record decisions and the data used to make
them• Analyze the results and improve the process
where possible• Learn - individually and organizationally
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Software Engineering Products and Processes
The software customer wants
quality software products at reasonable prices
The software producer wants
a well managed software production process
that consistently produces quality software
in a cost-effective manner
Some organizations have a defined and managed software engineering process
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The Software Process • The software product is created as part of the
Software Engineering Process
Definition:– the Software Process is a description of the
process which guides the software engineers as they work
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The Software Product Composed of programs, data and documents Delivers hardware computing potential Delivers information
Software Product Characteristics» developed or engineered,
not manufactured» doesn’t wear out» most is custom built
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The Software Process The set of activities which produce a software
product
The sequence of steps to develop and maintain software
Sets out the technical and management framework for applying methods, tools and people to the software task
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A Layered Technology
tools
methods
process
a quality focus
Software Engineering
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The Software Process ...
Software Engineering Layers Quality Focus - bedrock of SE Process
» defines a framework as a basis for management control of projects and context for technical methods
Methods
» technical ‘how to’ for building software Tools
» automated support for the process and the methods
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The Software Process ...
There is no ‘right’ or ‘wrong’ software process. The ‘wrong’ process reduces the quality or usefulness of the product
Software processes are complex and involve a large number of activities
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The Software Process ...Generic Phases (Pressman) Definition Phase focuses on ‘what’ Development Phase focuses on ‘how’ Maintenance Phase focuses on change
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The Software Process ...Has a common process framework containing: framework activities - for all software projects
work tasks project milestones software work products and deliverables quality assurance points
umbrella activities - occur throughout the process software quality assurance software configuration management software metrics or measurement
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A Common Process FrameworkCommon Process Framework
Framework Activities
Task sets
Tasks
Milestones, deliverables
SQA points
Umbrella activities
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Software Process Models ...
Evolutionary development Linear or waterfall model Prototyping (throw away) Rapid Application Development Incremental Process Spiral Model Concurrent Development Model Fourth Generation Techniques Extreme Programming
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SDLC - the reality
Overlapping phases Large, complex systems are usually broken into
subsystems and other smaller components Each subsystem may have its own mini-lifecycle. In reality there will be a continuous stream of
change requests.
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Process as Problem Solving
statusquo
problemdefinition
technicaldevelopment
solutionintegration
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Linear Models - Problems
• Change handling during the process
• Requires that all requirements are stated clearly at the beginning of the process
• Working version is delivered at the end of the process cycle; mistakes at earlier stages may be disastrous
• “Blocking States”
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Iterative Models - Prototyping
listento
customerbuild/revise
mock-up
customertest-drivesmock-up
Prototyping
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Prototyping - The Problems
• There is a “working version” of software before the requirements for the overall quality and maintainability are satisfied.
• Implementation compromises, made to create a quick “working version” often become a part of the final version.
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Iterative Models - RAD
businessmodeling
datamodeling
processmodeling
applicationgeneration
testing&
turnover
businessmodeling
datamodeling
processmodeling
applicationgeneration
testing&
turnover
businessmodeling
datamodeling
processmodeling
applicationgeneration
testing&
turnover
team #1
team #2team #3
60 - 90 days
Rapid Application Development (RAD)
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RAD - The Problems
• For large, but scalable projects, requires significant human resources
• Requires customers and developers willing to work in a rapid development environment
• If the requirements can not be modularized, this approach may not be suitable
• If fine-tuning is needed, this approach may not be suitable
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Evolutionary Models - The Incremental Model
analysis design code test
System/informationengineering
analysis design code test
analysis design code test
analysis design code test
increment 2
increment 3
increment 4
increment 1
delivery of1st increment
delivery of2nd increment
delivery of3rd increment
delivery of4th increment
calendar time
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Evolutionary Models - Spiral Model
CustomerCommunication
Planning
Construction & ReleaseCustomerEvaluation
Engineering
Risk Analysis
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Spiral Model - The Lifecycle of SW Product
• Concept Development Projects
• New Product Development Projects
• Product Enhancement Projects
• Product Maintenance Projects
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Spiral Model - Characteristics
Advantages
• application in large systems and software
• used well as a risk reduction mechanism
Disadvantages
• controllability (demands high risk assessment and expertise)
• has not been applied as much (little history)
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Component Assembly Model
CustomerCommunication
Planning
Construction & ReleaseCustomerEvaluation
Engineering
Risk Analysis
extract components if available
build components if available
construct nth
iteration of the system
identify candidate components
look up components in
library
put new components in
library
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Concurrent Model
none
Under development
Under development
Baselined
Done
Under revision
Awaiting changes
Analysis activity
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Still Other Process Models
• Formal methods—the process to apply when a mathematical specification is to be developed
• Cleanroom software engineering—emphasizes error detection before testing