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CS351 - Software Engineering (AY2004) 2
Software lifecycle “student view”
Design &Specification
Coding
Testing(optional)
Hand it in
>90%
<10%
CS351 - Software Engineering (AY2004) 3
Comments• The “student lifecycle model” clearly has many
limitations:– It doesn’t always earn you the grades you want.– It doesn’t scale.– You have little assurance of quality – somewhat of an
issue for paying customers!– It isn’t consistent.
• We need a better model, a better process to follow, to give us a chance of delivering quality code in a timely manner.
CS351 - Software Engineering (AY2004) 4
Software production process models• Ad–hoc approach: “Code and Fix”
– intuitive “model”– undesirable even for small tasks– impossible for large tasks
• Many formal process models exist– Waterfall Model– Spiral Model– Prototyping/Evolutionary Model
Build first version
Modify untilClient is satisfied
Operations mode
Retirement
Development
Maintenance
CS351 - Software Engineering (AY2004) 5
Waterfall model – overview• A process model addresses these questions:
– What shall we do next?– How long shall we continue to do it?
• A framework for software development methodology• Clearly identifies
– Deliverables– Standards
• Waterfall model provides a sequential, linear flow between phases
CS351 - Software Engineering (AY2004) 6
Minimal waterfall model
Analysis
Design
Code
Testing
Maintenance
CS351 - Software Engineering (AY2004) 7
Waterfall model – requirements stages
• Feasibility study– Cost/benefit analysis– Needs understanding of problem– Deliverable - a feasibility study document
• Costs alternative solutions• Requirements
– Analysis• Functionality etc of software
– Specification document• “Contract” between customer and software
engineers• Complete, precise, modifiable• Specifies
– Functional requirements– Non-functional requirements– Development and maintenance procedures
CS351 - Software Engineering (AY2004) 8
Waterfall model – final stages• Design and specification
– Modules• Preliminary and detailed design
– Deliverable - design specification document– Standards
• Coding and module testing– Deliverable - tested modules– Standards for coding and testing, quality control
• Integration and system testing– Delivers running application - alpha tested within
organization
CS351 - Software Engineering (AY2004) 9
Waterfall model – final stages• Delivery and maintenance
– Beta testing then product delivery– Maintenance
• Problems– Time between requirements and maintenance
phases– Integrating changes into correct phases
CS351 - Software Engineering (AY2004) 10
Detailed waterfall model
RequirementsVerify
SpecificationVerify
PlanningVerify
DesignVerify
ImplementationTest
IntegrationTest
Operations Mode
Retirement
ChangedRequirements
Verify
Development
Maintenance
CS351 - Software Engineering (AY2004) 11
Waterfall model – example/analysis• Documentation, verification and management
– “Document driven"– Quality control: reviews, walk-throughs and
inspections– Management: methodology, configuration and
personnel• Analysis
– Linear, rigid, monolithic– Disciplined– Disadvantages
• Commitments too early• Rigidity and linearity make feedback difficult• Change often achieved as a "fix": distorts
maintenance phase• Somewhat bureaucratic
CS351 - Software Engineering (AY2004) 12
Waterfall model - realityRequirementsanalysis
Systemdesign
Programdesign
Programimplementation
Unittesting
Integrationtesting
System testing
Delivery
Maintenance
CS351 - Software Engineering (AY2004) 13
Rapid prototyping model
Rapid PrototypingVerify
SpecificationVerify
PlanningVerify
DesignVerify
ImplementationTest
IntegrationTest
Operations Mode
Retirement
ChangedRequirements
Verify
Development
Maintenance
CS351 - Software Engineering (AY2004) 14
Evolutionary model
RequirementsVerify
SpecificationVerify
PlanningVerify
ArchitecturaldesignVerify
For each build: perform detailed design, implementation and integration. Test. Deliver to client
Operations Mode
Retirement
Development
Maintenance
CS351 - Software Engineering (AY2004) 15
Evolutionary model• Incremental development to
– Deliver partial functionality early (non-monolothic)– Provide feedback on requirements
• May be associated with incremental delivery– Delivered increment is a product– User provides feedback for design of next increment
• Approach may be combined with waterfall model– During implementation phases
• Requirements document identifies subsets• Allowance for later change
– At all stages• Finer grained application of waterfall model to
each increment
CS351 - Software Engineering (AY2004) 16
Evolutionary model – prototyping• Prototyping
– “Throw-away”• Build system once - as basis for understanding
requirements• Discard and rebuild
– Build-upon• Iterative process
– Decide objectives of prototype– Plan, build and document prototype– Evaluate prototype
• Eventually refine into a completed system• Provides feedback on requirements and functionality • Facilitates understanding of requirements and interfaces• Flexible• Inherently less disciplined - needs careful management
CS351 - Software Engineering (AY2004) 17
Evolutionary model – prototyping
Specification DesignImplementation & Integration
Deliver to client
Specification DesignImplementation & Integration
Deliver to client
Specification DesignImplementation & Integration
Deliver to client
Build 1
Build n
Build 3
Build 2
Specification teamDesign team
Implementation/integration team
Specification DesignImplementation & Integration
Deliver to client
......
...
CS351 - Software Engineering (AY2004) 18
Spiral model
Verify
Verify
VerifyVerify
VerifyRiskanalysis
Riskanalysis
Riskanalysis
Riskanalysis
Riskanalysis
R.A.
Rapidprototype
Specification
Implementation
Design
Planning
Integration
CS351 - Software Engineering (AY2004) 19
Spiral model• A Meta–model really
– Any of the other process models can be used with it• Cyclic, not linear• Attempts to identify risks• Usually coupled with prototyping• Each “turn” around the spiral resolves more risks and
(possibly) yields a prototype
CS351 - Software Engineering (AY2004) 21
Is it worth it?• Estimates for a 200,000 line data processing product:
CMM Duration Effort Faults detected Faults delivered Total costLevel (months) (person during to client of
months) development and installed developmentLevel 1 29.8 593.5 1348 61 $5,440,000Level 2 18.5 143.0 328 12 $1,311,000Level 3 15.2 79.5 182 7 $728,000Level 4 12.5 42.8 97 5 $392,000Level 5 9.0 16.0 37 1 $146,000
• CMM = Capability Maturity Model• CMM is a measure of an organizations ability to follow a
process and refine it to suit that organization’s activities. It is covered in more detail in CS460.
CS351 - Software Engineering (AY2004) 22
Observations• We need to understand the software development
lifecycle and have a process in place to help us deliver software on-time and within budget.
• Error rates and cost of development decrease the more we understand the software process.
• While discussion on requirements gathering etc is defered until CS460, we can certainly do a great deal to improve our own software by understanding what we do when we build software systems.
• As individuals, we most likely follow one of the lifecycle models described earlier – or a hybrid of one or more of the models.
• We may skip some steps, we may not pay sufficient attention to some aspects.
CS351 - Software Engineering (AY2004) 23
Our behavior• A better understanding of our personal behavior will
help us fit into a team environment better, and will help us deliver higher quality code.
• To understand what we do, we must objectively assess what we do.– This is difficult as we first have to overcome our
belief that we are doing everything correctly.– We have to examine what we do and constantly ask
“how can I improve?”– We have to measure what we do in order to know if
the changes we make are working, and to identify those aspects of our behavior that require change.
CS351 - Software Engineering (AY2004) 24
Personal software process• We have already seen the personal software process as
a means to identify several of the common errors we make.
• You should apply the PSP to all code you write – not just for this subject.
• Over time you will gather the information on yourself that you need to see what needs improving.– It will then, of course, be up to you to address those
deficiencies and improve.– You should continue to use the PSP to measure the
success of your changes and to identify further areas for improvement.
CS351 - Software Engineering (AY2004) 25
Journal• If addition to the use of the PSP, we also recommend you
need a journal.• A journal is where you record all of your thoughts, design
your algorithms, plan the testing strategy for these algorithms, make notes on the performance of your code, make notes on the kinds of errors you make, record how you ntend to rectify these deficiencies, …
• You record everything related to software development. • You should throw nothing away. Ideally, the journal is a
bound book with numbered pages.• At regular intervals (every few months), you should read
through your journal and look for trends, look for errors you regularly make, look for things you don’t understand.
• Once identified, plan a strategy to deal with these issues – record the plan in the journal and stick to it.
CS351 - Software Engineering (AY2004) 26
Summary• This course focuses on your personal ability to produce
high quality software.• You should make observations in your journal of errors
you make including:– Not fully understanding the requirements– Poor testing– Typical coding errors– Poorly designed interfaces– Integration issues
• These are all aspects of the software lifecycle• If we can get things right as an individual, we have a
better chance of getting things right in a team.
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