Benefits of Reengineering a legacy system
A lthough many application development tool vendors emphasize new development in the form of tools to drive multi-tier application development or web-enablement, the notion of how to leverage past IT investments has largely been overlooked. Since business rules define the active policy of an organization, an ability to identify, understand and leverage these rules is a key prerequisite to evolving an organizations IT infrastructure.
Until recently, software engineering concentrated almost exclusively on the definition and improvement of the software development process. And this produced a lot of important results, ranging from structured analysis, to object oriented analysis, domain and component analysis, CASE environments, etc., which are very useful in developing new systems and forward engineering existing systems well maintained and documented. But legacy systems, created prior these methodologies and tools, usually are very poor in documentation and suffer of years of personnel change and ad-hoc maintenance interventions. This is where reengineering steps in.
Reengineering is the systematic transformation of an existing system into a new form to realize quality improvements in operation, system capability, functionality, performance, or evolvability at a lower cost, schedule, or risk to the customer.
This definition emphasises the focus that reengineering puts on improving existing systems with a greater return of investment (ROI) than could be obtained through a new development.
Reengineering is closely related to traditional maintenance, as defined by ANSI-IEEE: maintenance entails making corrective, perfective, and adaptive changes to software, while development focuses on implementing new capabilities, adding functionalities, or making substantial improvements typically by using new computer resources and incorporating new software technologies; reengineering spans the gap between these two activities and exhibits characteristics of both.Reengineering Benefits
Lower costs. Evidence from a number of US projects suggests that reengineering an existing system costs significantly less than new system development. Ulrich, for example reports on a reengineering project that cost $12 million, compared to estimated redevelopment costs of $50 million.
Lower risks. Reengineering is based on incremental improvement of systems, rather than radical system replacement. The risk of losing critical business knowledge, which may be embedded in a legacy system, or of producing a system that does not meet its users real needs, is drastically reduced.
Better use of existing staff. Existing staff expertise can be maintained, and extended accommodate new skills during reengineering. The incremental nature of reengineering means that existing staff skills can evolve as the system evolves. The approach carries less risk and expense which is associated with hiring new staff.
Revelation of business rules. As a system is reengineered, business rules that are embedded in the system are rediscovered. This is particularly true where the rules govern exceptional situations.
Incremental development. Reengineering can be carried out in stages, as budget and resources are available. The operational organisation always has a working system, and end users are able to gradually adapt to the reengineered as it is delivered in increments.
S oftware reengineering is often associated with business process reengineering (BPR). They should not however been confused. Software reengineering is the improvement of software systems. The objective of BPR is to increase the efficiency of an organisations business processes. BPR is however, often a precursor to software reengineering.
It is important to view legacy systems from the greater perspective of BPR. Software reengineering is of little value if the software system is being improved in a way, which is not suited to the business process in which the system operates.
Many of todays legacy systems were developed to support dated bureaucratic and hierarchical organisational structures. Organisations have generally changed their ways of working to be more productive and reduce their running costs. Unless the legacy systems change to support new working practices, they become a hindrance to them, rather than support them.
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