Software Maintenance

Table of Contents

1. Introduction
2. Software Configuration Management
3. Software Maintenance Activities
4. Software Maintenance Characteristics
   1. Activities
      1. Unstructured Maintenance
      2. Structured Maintenance
   2. Costs

Introduction

• The maintenance of existing software can account for over 60 percent of all development effort.
• Because change is inevitable, mechanisms must be developed for evaluating, controlling and making modifications.
• Maintenance is a set of software engineering activities that occur after software has been delivered to the customer and put into operation.
• 70 per cent of the cost of software is devoted to maintenance.
• Maintenance activities can be divided into two types:
  1. Modification
     • As the specifications of computer systems change, reflecting changes in the external world, so must the systems themselves.
  2. Debugging
     • Removal of errors that should never have been there in the first place.
• More than two-fifths of maintenance activities are extensions and modifications requested by the users.
• The magnitude of this proportion seems to reflect the lack of extendibility of commonly implemented software.
• Changes in data formats is the next largest activity. The issue is not that some part of the program knows the physical structure of the data but that this knowledge is usually spread out over too many parts of the system.
• Emergency bug fixes cost more than routine, scheduled corrections. They are performed under pressure, disrupt the orderly process of delivering new releases and tend to introduce new errors.

Software Configuration Management

• Software configuration management activities are developed to identify change, control change, assure that change is being properly implemented, and report change to others who may have an interest.
• SCM is a set of tracking and control activities that begin when a software development project begins and ends only when the software is retired.

Software Maintenance Activities

• Maintenance can be defined as four activities:
  1. Corrective Maintenance
     • A process that includes diagnosis and correction of errors.
  2. Adaptive Maintenance
     • Activity that modifies software to properly interface with a changing environment (hardware and software).
  3. Perfective Maintenance
     • Activity for adding new capabilities, modifying existing functions and making general enhancements.
     • This accounts for the majority of all effort expended on maintenance.
  4. Preventive Maintenance
     • Activity which changes software to improve future maintainability or reliability or to provide a better basis for future enhancements.
     • Still relatively rare.
• Distribution of maintenance activities (based on a study of 487 software development organizations):
  • Perfective: 50%
  • Adaptive: 25%
  • Corrective: 21%
  • Others: 4%

Software Maintenance Characteristics

1. The activities required to accomplish the maintenance phase and the impact of a software engineering approach (or lack thereof) on the efficacy of such activities.
2. The costs associated with the maintenance phase.
3. The problems that are frequently encountered when software maintenance is undertaken.

Activities

Unstructured Maintenance

If the only available element is the source code:

• painstaking evaluation of the code, complicated by poor internal documentation,
• things such as program structure, global data structures, system interfaces, performance and/or design constraints are difficult to ascertain and frequently misinterpreted,
• ramifications of changes to the code are difficult to assess,
• regression tests are impossible to conduct because no record of testing exists.

Structured Maintenance

• Begins with an evaluation of the design documentation.
• The impact of required modifications or corrections is assessed and an approach is planned.
• The design is modified and reviewed, new source code is developed and regression tests are conducted.

Maintenance Costs

• Typical software organizations spend anywhere from 40 to 70 percent of all funds conducting maintenance.
• Maintenance-bound organizations result --> loss or postponement of development opportunities.
• Customer dissatisfaction when requests cannot be addressed.
• Reduction in overall software quality as a result of changes that introduce latent errors in the maintained software.