A method for assessing legacy systems for evolution

Legacy systems are usually critical to the business in which they operate, but the costs of running them are often not justifiable. Determining whether such systems are worth keeping requires an overall assessment of the system. We present an assessment method that examines a legacy system from its technical, business and organisational perspectives. The method guides users through assessment of these perspectives by selecting assessment characteristics and assigning values to them. The method provides further guidance on interpreting the results obtained from assessment. Our assessment method can be tailored to the needs of particular evolution projects and organisations. It is not prescriptive of particular tools and techniques, and can be instantiated to offer a cost/risk trade-off. Quick estimates can be derived from performing the method at a high level. The risk of producing an inaccurate assessment can be reduced by further iterations of the method performed at more detailed levels.