Software maintenance

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In software engineering, software maintenance is the modification of a software product after delivery to correct faults, to improve performance or other attributes, or to adapt the product to a modified environment.”(ISO/IEC 14764). This international standard describes the 6 software maintenance processes as:

  1. The implementation process contains software preparation and transition activities, such as the conception and creation of the maintenance plan, the preparation for handling problems identified during development, and the follow-up on product configuration management.
  2. The problem and modification analysis process, which is executed once the application has become the responsibility of the maintenance group. The maintenance programmer must analyze each request, confirm it (by reproducing the situation) and check its validity, investigate it and propose a solution, document the request and the solution proposal, and, finally, obtain all the required authorizations to apply the modifications.
  3. The process considering the implementation of the modification itself.
  4. The process acceptance of the modification, by checking it with the individual who submitted the request in order to make sure the solution provided a solution.
  5. The migration process (platform migration, for example) is exceptional, and is not part of daily maintenance tasks. If the software must be ported to another platform without any change in functionality, this process will be used and a maintenance project team is likely to be assigned to this task.
  6. Finally, the last maintenance process, also an event which does not occur on a daily basis, is the retirement of a piece of software.

There are a number of processes, activities and practices that are unique to maintainers, for example:

  • Transition: a controlled and coordinated sequence of activities during which a system is transferred progressively from the developer to the maintainer;
  • Service Level Agreements (SLAs) and specialized (domain-specific) maintenance contracts negotiated by maintainers;
  • Modification Request and Problem Report Help Desk: a problem-handling process used by maintainers to prioritize, documents and route the requests they receive;
  • Modification Request acceptance/rejection: modification request work over a certain size/effort/complexity may be rejected by maintainers and rerouted to a developer.

A common perception of maintenance is that it is merely fixing bugs. However, studies and surveys over the years have indicated that the majority, over 80%, of the maintenance effort is used for non-corrective actions (Pigosky 1997). This perception is perpetuated by users submitting problem reports that in reality are functionality enhancements to the system.

Software maintenance and evolution of systems was first addressed by Lehman in 1969. Over a period of twenty years, his research led to the formulation of eight Laws of Evolution (Lehman 1997). Key findings of his research include that maintenance is really evolutionary developments and that maintenance decisions are aided by understanding what happens to systems (and software) over time. Lehman demonstrated that systems continue to evolve over time. As they evolve, they grow more complex unless some action is taken to reduce the complexity.

E.B. Swanson initially identified three categories of maintenance: corrective, adaptive, and perfective. These have since been updated and ISO/IEC 14764 presents:

  • Corrective maintenance: Reactive modification of a software product performed after delivery to correct discovered problems.
  • Adaptive maintenance: Modification of a software product performed after delivery to keep a software product usable in a changed or changing environment.
  • Perfective maintenance: Modification of a software product after delivery to improve performance or maintainability.
  • Preventive maintenance: Modification of a software product after delivery to detect and correct latent faults in the software product before they become effective faults.

The key software maintenance issues are both managerial and technical. Key management issues are: alignement with customer priorities, staffing, which organization does maintenance, estimating costs. Key technical issues are: limited understanding, impact analysis, testing, maintainability measurement.

Software Maintenance Capability Maturity models which address the unique processes of the software maintainers are described in the Software Maintenance Maturity Model (S3M), The corrective maintenance maturity model (Kajko-Mattsson 2001), the IT Service CMM and to be released CMMi for Services (SEI 2008).