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Software Maintenance. William W. McMillan. 24 March 2013. Who wants to do software maintenance? If this is not your cup of tea, why not?. Software “Evolution”. Term is a good one. But can be confused with “evolutionary development.”

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Software Maintenance

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Software maintenance

Software Maintenance

William W. McMillan

24 March 2013

Who wants to do software maintenance if this is not your cup of tea why not

Who wants to do software maintenance?If this is not your cup of tea, why not?

Software evolution

Software “Evolution”

  • Term is a good one.

  • But can be confused with “evolutionary development.”

  • Focus here is on what happens to software after initial delivery.

  • Yes, it evolves, but only after it was created intentionally.

  • “Maintenance” has been most common term.

Most software effort is here

Most Software Effort is Here

  • Systems may be around for decades.

  • Adding functional increments much harder in older systems than in brand new.

  • Have to deal with loss of:

    • Tools and platforms

    • Knowledge (developers, management, users)

    • Ways of working (e.g. plan-based to agile)

    • Conducive environment (leadership, access to users, team energy,…)

What difficulties have you had in changing software after initial creation

What difficulties have you had in changing software after initial creation?

Kinds of maintenance old

Kinds of Maintenance (Old)

  • Corrective (~ 20%)

    • Fixing errors

  • Adaptive (up to 25%)

    • New software or hardware environment

  • “Perfective” (50% +)

    • Enhancements, changes in requirements

  • Preventative (~ 0%)

    • Cleaning house, tidying up, documenting

Kinds of maintenance newer

Kinds of Maintenance (Newer)

  • Fault repair (17%)

    • Fixing errors

  • Environmental adaptation (18%)

    • New software or hardware environment

  • Functionality addition, modification (65%)

    • Enhancements, changes in requirements

  • Preventative (~ 0%)

    • Cleaning house, tidying up, documenting

What could be done to encourage preventative maintenance

What could be done to encourage preventative maintenance?

The payoff for good engineering

The Payoff for Good Engineering

  • Most of software engineering supports maintenance.

  • More effort early leads to easier maintenance.

  • One estimate:

    • over 80% of maintenance effort caused by incorrect requirements and specs.

  • Key in getting management support for software engineering.

Cost of maintenance

Cost of Maintenance

  • Proportion of code changed per year times original cost of system.

  • Annual maintenance effort =

    annual change traffic *

    software development time

  • AME = ACT * SDT(in person-months)

  • Oversimplification – need to consider all other COCOMO factors.

What has to be maintained

What Has To Be Maintained

  • Code.

  • Databases.

  • Documents:

    • Requirements, user manuals, help files, design documents.

  • Installations:

    • Workstations, mobile devices, embedded systems.

  • V & V records, test data sets.

  • Archives

    • Past system configurations, management docs, changes.

Why is maintenance hard

Why is maintenance hard?

Challenges in maintenance

Challenges in Maintenance

  • Hard to get resources for good software engineering to begin with.

  • Hard to get resources to maintain old stuff.

  • Lose knowledge of system and domain expertise.

  • People don’t like to do it.

  • … ?

Lehman belady s laws

Lehman & Belady’s “Laws”

  • Continuing change

    • Nothing in software is static: OSs, needs, delivery modes…

  • Increasing complexity

    • When has a system ever gotten simpler?

  • Continuing growth

    • Need growing functionality to satisfy users and clients.

  • Declining quality

    • Counter-examples?

Lehman belady s laws1

Lehman & Belady’s “Laws”

  • Large program evolution is “self-regulating”

    • Can’t push change beyond a natural limit.

  • Conservation of familiarity

    • Systems maintain their basic character

    • … any examples of those that change drastically?

Any other software laws you can think of

Any other software “laws” you can think of?

Software re engineering

Software Re-Engineering

  • Reimplementation of major parts or all.

  • Legacy systems have old..

    • languages, hardware, OSs, coding practices, algorithms, interfaces

  • Over 1011 lines of code in existence.

  • Heavy reliance on old systems.

Software re engineering1

Software Re-Engineering

  • Understand intent of present system.

    • Documents, domain, context of use

  • Recover architecture and abstractions.

  • Use reverse engineering tools.

  • Find interactions, dependencies, coupling, redundancies.

  • Understand algorithms.

    • Especially if speed, memory use or similar at issue.

  • Interviewing people is critical (if they’re around!).

Software re engineering2

Software Re-Engineering

  • Re-implement (part or whole).

  • Translate to new programming language (auto?).

  • Refactor, restructure system.

  • Improve algorithms.

  • Add exception handling.

  • Improve security.

Software re engineering3

Software Re-Engineering

  • Switch paradigm, say to object-oriented or functional.

  • Improve robustness and quality (reduce coupling, better style, etc.).

  • Improve V & V.

  • Update documents.

Have you ever had to recover software architecture from code alone

Have you ever had to recover software architecture from code alone?

Data re engineering

Data Re-Engineering

  • Newer file formats, directory structures.

  • Change field types, sizes, etc.

  • Improve numeric precision.

  • Improve validation rules.

  • Establish or change default values.

  • Change units of measurement.

  • Implement new data model (e.g., relational).

  • Modify database keys & indexing.

  • Normalize database.

What data re engineering has been necessary in recent years for many systems

What data re-engineering has been necessary in recent years for many systems?

User experience re engineering

User Experience Re-Engineering

  • Beyond incremental requirements enhancement.

  • Changes in platform, user interface, deployment, connections among users.

  • Examples?

  • Challenges?

  • Advice?

Guidelines for sw maintenance

Guidelines for SW Maintenance

  • Expect it, plan for it.

  • Use good people and pay them well.

  • Understand the system thoroughly:

    • Architecture, algorithms, V & V done, domain.

  • Isolate changes, change minimally.

  • Use regression testing.

Guidelines for sw maintenance1

Guidelines for SW Maintenance

  • Update documents.

    • Requirements, specs, V & V records

  • Control and release versions carefully.

  • Allow user input via bug reports, change requests.

  • Use software tools to support the process.

Other maintenance guidelines

Other maintenance guidelines?



Your software engineering group is called in to help a company evaluate its software maintenance operation. What six to 12 indicators would you look at to assess the state of their operation? If you can, give quantitative measures you would like to see.

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