How do I evaluate two existing legacy information systems?

(skills tutorial)

Before we can assess existing legacy information systems, we need to understand what a legacy information system is. If you know what one is, then read on. If not, find out here.

At some point, you will be faced with one or more legacy systems. This will affect what you do, in as much as you have an existing system to consider. Of course 'existing system' does not just mean the software itself - it encompasses all the working practices, informal communication channels and 'the way people do things'.

Being aware of this means that you can plan ahead and pre-empt some of the foreseeable difficulties.

So, you are responsible for an organisation's information system and there is one or more existing legacy systems in place. What can you do?

Start Again

You could just forget the existing stuff and start afresh with a new system. This would allow you to specify exactly what is required, and develop the system to serve the organisation's needs. However, there is the cost of the new system to consider, a lengthy selection process, staff to re-train as well as planning for what to do if the chosen package doesn't satisfy all of your requirements (they rarely do).

This option is quite drastic and only practical when the existing systems are failing to deliver. Many organisations change their business processes to suit the information system - this is far from ideal, as the information should support the business, not the other way around.

Accept the Situation

You could carry on and maintain what is already in place. This is fine if the existing functionality is present in the system, and the working environment is fairly stable.

Modify the Existing System

Modifying existing systems gives the opportunity to transform, tailor and evolve systems to suit the organisation. This is a pragmatic approach, especially when the working environment changes frequently. However, after only a short while the system is unique, with the organisation becoming increasingly dependent on its employees.

In most situations we find ourselves considering at least two of the options. Upfront investment usually determines whether the system will be totally replaced or not. Many organisations are willing to accept greater expenditure in the longer term, to reduce short-term disruption.

Essentially we should consider two perspectives:

1. What is the business value of the system, and
2. How does the quality of the system affect its maintainability.

If we consider the legacy systems from both perspectives, then we are in much better position to be able to make an informed judgement.

The diagram below illustrates the relationship between business value and system quality. This does assume that we are able to perform an adequate and objective assessment of the existing systems.

Assessment of Business Value

In the majority of instances the assessment of value to a business is subjective. The best way to attempt to get a balanced viewpoint is to approach the assessment from different angles. Typical views can be obtained from:

• Users
• Customers
• Line managers
• IT managers
• Senior managers

Assessment of System Quality

Whilst this is similar to the assessment of business value, you will find that you have to ask specific questions about the business processes themselves. This will give some idea as to the effectiveness of the system in supporting the business activities.

It is a good idea to consult the various categories of people as described above. Some example questions that you might ask are:

• Is the existing process modelled? Are there procedures to ensure that the model is adhered to/complied with?
• Do different departments have the same processes for the same functions?
• Have the people adapted their work to suit the system?
• Are relationships with other business processes necessary?
• Is the process effectively supported by the legacy application software? Does the process require the same data to be entered several times in different places?

Once these questions have been answered we can look a little bit deeper. Specifically, we consider the environment and the application software within it.

Summary

• The business value and quality of application software should be considered to help decide whether to replace, transform or maintain the system.
• The business value of a system is a measure of how effective that system is at supporting the business.
• The quality of a system is dependent on the quality of the business processes, the quality of the application software and the quality of the hardware and software used to support the system.

Reference: Software Engineering, Sixth Edition, Ian Sommerville, Addison Wesley, ISBN 0-201-39815-X

Review Questions

Test your understanding of this topic with the following questions.

Why are legacy systems important for the organisation?

Suggest ten questions that might be put to end-users of a system when carrying out a business process assessment.