Lehman has given eight laws for E-Type software evolution –
● Continuing change – An E-type software system must continue to adapt to the real world changes, else it becomes progressively less useful.
● Increasing complexity – As an E-type software system evolves, its complexity tends to increase unless work is done to maintain or reduce it.
● Conservation of familiarity – The familiarity with the software or the knowledge about how it was developed, why was it developed in that particular manner etc. must be retained at any cost, to implement the changes in the system.
● Continuing growth- In order for an E-type system intended to resolve some business problem, its size of implementing the changes grows according to the lifestyle changes of the business.
● Reducing quality – An E-type software system declines in quality unless rigorously maintained and adapted to a changing operational environment.
● Feedback systems- The E-type software systems constitute multi-loop, multi-level feedback systems and must be treated as such to be successfully modified or improved.
● Self-regulation – E-type system evolution processes are self-regulating with the distribution of product and process measures close to normal.
● Organizational stability – The average effective global activity rate in an evolving E-type system is invariant over the lifetime of the product.