What is maintenance?

I have been doing some work analysing some legacy systems, some old some brand new, yes it is possible to write a brand new legacy system!

I thought it would be good to define what maintenance is and what can be done to make it a less painful exercise down the road.

After a product has been released, the maintenance phase keeps the software up to date with environment changes and changing user requirements.

The earlier phases should be done correctly so that the product is easily maintainable. The design phase should plan the structure in a way that can be easily altered. Similarly, the implementation phase should create code that can be easily read, understood, and changed.

Maintenance can only happen efficiently if the earlier phases are done properly. There are three major problems that can slow down the maintenance process: unstructured code, maintenance programmers having insufficient knowledge of the system and documentation being absent, out of date, or at best insufficient.

The success of the maintenance phase relies on these problems being fixed earlier in the life cycle.
Maintenance consists of four parts.

Corrective maintenance deals with fixing bugs in the code. Adaptive maintenance deals with adapting the software to new environments. Perfective maintenance deals with updating the software according to changes in user requirements.

Finally, preventive maintenance deals with updating documentation and making the software more maintainable.
All changes to the system can be characterized by these four types of maintenance. Corrective maintenance is ‘traditional maintenance’ while the other types are considered as ‘software evolution.’

As software systems age, it becomes increasingly difficult to keep them ‘up and running’ without maintenance.
There is direct financial cost of not maintaining software systems, and in fact, a substantial proportion of the resources expended within the Information Technology industry go towards the maintenance of software systems.
In order to increase the maintainability of software, we need to know what characteristics of a product affect its maintainability.

There has been a great deal of speculation about what makes a software system more difficult to maintain. There are some program characteristics that are found to affect a product’s maintainability

Factors include system size, system age, number of input/output data items, application type, programming language, and the degree of structure.
Larger systems require more maintenance effort than do smaller systems, because there is a greater learning curve associated with larger systems, and larger systems are more complex in terms of the variety of functions they perform.

Older systems require more maintenance effort than do younger systems, because software systems tend to grow larger with age, become less organized with changes, and become less understandable due to staff turnover.
The factors that decrease maintenance effort can be summarised into the list below:
· Use of structured techniques
· Use of modern software
· Use of automated tools
· Use of data-base techniques
· Good data administration
· Experienced maintainers.