Abstract
Systems that were developed in the reign when there were no modern techniques of software development are said to be legacy systems. These systems have a greater business value for several organizations and have significantly served the organizations and delivered the intended result. However these systems have weak requirement engineering process which makes its understanding difficult and also makes it maintenance complicated and less efficient in terms of performance. Frequent requirements change makes it more difficult for the maintainers of such systems as these systems lacks in embracing the change due to its out dated and non-flexible structure. Due to preservation these systems costs heavily for the organizations that are still banking on it. Also at times making tiny changes to these systems got so complicated that it can make maintainers life full of problems. On assessment of legacy system if it is found difficult to preserve further, losing business value, not embracing change, preservation costs going higher, reduced functionality and performance, no access to business content and is no further has the ability to be reconfigured then it's the time for this system to be scrapped completely, carrying on frequent maintenance, rewrite some of the parts of it or reconstitute from the beginning, but selection of the mentioned strategies totally banks on the technical state of the system.
Beside discarding system completely and reconstitution from the beginning modern development strategies include strategies that facilitate legacy system with rewriting a part of the particular system, reusing a part or full previously used systems. These strategies are known as software reengineering and software reuse. These approaches not only reduce risk of developing a new system but also reduce cost and accelerate product production.