CS 5150Software

EngineeringLecture 3

Software Processes 2

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Project Teams

• I will send out project suggestions this afternoon

• You should have a team soon

• Send email to Ben & Yue when you have (most of) a team

• Team name

• Names of team members

• Client info

• Project topic

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Projects

• Project suggestions continuing to come in

• You should have contacted a client by next week

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Project Details

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Software Processes in More Detail

• Feasibility and planning

• Requirements

• System and program design

• Implementation

• Acceptance and release

• Operation and maintenance

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Feasibility

• A feasibility study precedes the decision to start a project

• What is the scope of the project?

• What relevant experience to the participants have?

• Projected benefits?

• Projected costs, risks, timetable?

• Beware McConnell’s wicked problem

• But don’t appeal to it too quickly

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Feasibility for 5150

• Mostly a scoping aid

• Sketch out projected work

• More in next lecture

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Requirements

• Define the system’s behavior from the client’s perspective

• Higher resolution than feasibility study

• Priorities -- relative importance

• Can be developed before design or incrementally

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System and Program Design

• Define the system from the implementer’s perspective

• System design (or architecture)

• High level. Should fit on a white board for 5150

• Program design

• “Medium level”

• Source of much debate in software engineering

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Implementation (Construction)

• Actual coding

• Or acquisition and integration of existing code

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Acceptance and Release

• The system is tested against the requirements by the client

• The system is transferred to the client or made available to the public

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Operation and Maintenance

• Operation: The system is in active use

• Maintenance: Errors and other problems are identified and fixed or triaged

• Evolution: The system is changed in response to changing requirements and priorities

• This might involve a whole new cycle through a software process

• Phase out: Use of the system ends (abruptly or gradually)

• The software life cycle

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Three Categories of Testing

• User testing

• Using mock-ups, prototypes or the actual system to evaluate usability with real potential users

• Program testing

• The development team makes sure the system works as designed

• Acceptance testing

• The client compares the system with the requirements

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What is a Software Process?

• More or less formal rules for organizing work on software

• Trivial example:

• Meeting with client

• Meeting with team

• Code code code

• Test

• Email finished program to client

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Spectrum of Software Processes

• (Modified) waterfall model

• Iterative refinement

• Incremental (Agile)

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The Waterfall Model

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Iterative Refinement

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Incremental

• In each increment (sprint) the team works through the full software development cycle and ends up with new production-ready features

• Each sprint is assigned a fixed (and short) time frame, e.g. 4 weeks

• Team size involved in a sprint is usually small (5-10)

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Waterfall Discussion

• Pros

• Visibility and predictability

• Separation of tasks

• Quality control at each step

• Cost control at each step

• Cons

• Wicked problems

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Modified Waterfall

This is morerealistic

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Iterative Refinement Discussion

• Pros

• Complete (bare-bones) system done quickly

• Can correct mistakes in early design stages

• Cons

• Throw away a lot of code

• Can encourage feature bloat

• Can lead to half-done features

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Incremental Development Discussion

• Pros

• Leads quickly to production code

• Feedback benefits of iterative refinement, but even faster

• Minimizes wasted code

• Cons

• Haphazard high-level architecture

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“Choosing” a Process

• Often heavily influenced by the project’s environment

• Big bureaucracies often like waterfall

• End user software vendors usually do something like iterative refinement

• Internet applications often developed with an incremental process

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Thought Exercise

• Software process conversation dominated by commercial software developers

• Do these processes make sense for open source?

• What is open source? (Linux, Haskell compiler, Uncle Joe’s photo organizer)