Also visit our download section for a free security audit questionnaire. Legacy Systems is the name applied somewhat ironically to old software systems which have undergone years of maintenance. The characteristics of these systems result from the nature of software systems in general and of software maintenance in particular. People often express surprise that an artefact such as software should require maintenance. Every new type of bank account, mortgage, or insurance policy for example, will require changes to the organisation's suite of software.
Software systems are the most complex things ever created by mankind.
It can be shown, within the limits of probability, that evolving software systems become larger and more complex with time. Various factors conspire to render the documentation of the system and the understanding of its overall design increasingly out of step with the functional software. The last point is crucial. A well engineered system would have a set of library routines for date calculation and for the execution of the various manipulations to be performed on date codes. It would be reasonable to expect a newly delivered system to be structured in this way.