Software evolution


Software evolution :
The software is modified to adapt it to changing customer and market requirement.software evolution is important because organization has invested large amount of money in their software and are completely dependent on this software,where software evolution is triggered by changing businesses requirements by reporting of software defect or by changes to other system in a software system environment

General introduction

, in his key book The Mythical Man-Month, states that over 90% of the costs of a typical system arise in the maintenance phase, and that any successful piece of software will inevitably be maintained.
In fact, Agile methods stem from maintenance-like activities in and around web based technologies, where the bulk of the capability comes from frameworks and standards.
Software maintenance address bug fixes and minor enhancements and software evolution focus on adaptation and migration.
Software technologies will continue to develop. These changes will require new laws and theories to be created and justified. Some models as well would require additional aspects in developing future programs. Innovations and improvements do increase unexpected form of software development. The maintenance issues also would probably change as to adapt to the evolution of the future software. Software processes are themselves evolving, after going through learning and refinements, it is always improve their efficiency and effectiveness.

Basic concepts

The need for software evolution comes from the fact that no one is able to predict how user requirements will evolve a priori.
In other words, the existing systems are never complete and continue to evolve. As they evolve, the complexity of the systems will grow unless there is a better solution available to solve these issues. The main objectives of software evolution are ensuring functional relevance, reliability and flexibility of the system. Software evolution can be fully manual, partially automated or fully automated.
Software evolution has been greatly impacted by the Internet:
E.B. Swanson initially identified the
three categories of maintenance: corrective, adaptive, and perfective. Four categories of software were then catalogued by Lientz and Swanson.
These have since been updated and normalized internationally in the ISO/IEC 14764:2006:
All of the preceding take place when there is a known requirement for change.
Although these categories were supplemented by many authors like Warren et al. and Chapin, the ISO/IEC 14764:2006 international standard has kept the basic four categories.
More recently the description of software maintenance and evolution has been done using ontologies, Deridder, Vizcaíno, Dias, and Ruiz ), which enrich the description of the many evolution activities.

Stage model

Current trends and practices are projected forward using a new model of software evolution called the staged model. Staged model was introduced to replace conventional analysis which is less suitable for modern software development is rapid changing due to its difficulties of hard to contribute in software evolution. There are five distinct stages contribute in simple staged model.
Prof. Meir M. Lehman, who worked at Imperial College London from 1972 to 2002, and his colleagues have identified a set of behaviours in the evolution of proprietary software. These behaviours are known as Lehman's Laws, and there are eight of them:
  1. "Continuing Change" — an E-type system must be continually adapted or it becomes progressively less satisfactory
  2. "Increasing Complexity" — as an E-type system evolves, its complexity increases unless work is done to maintain or reduce it
  3. "Self Regulation" — E-type system evolution processes are self-regulating with the distribution of product and process measures close to normal
  4. "Conservation of Organisational Stability " - the average effective global activity rate in an evolving E-type system is invariant over the product's lifetime
  5. "Conservation of Familiarity" — as an E-type system evolves, all associated with it, developers, sales personnel and users, for example, must maintain mastery of its content and behaviour to achieve satisfactory evolution. Excessive growth diminishes that mastery. Hence the average incremental growth remains invariant as the system evolves.
  6. "Continuing Growth" — the functional content of an E-type system must be continually increased to maintain user satisfaction over its lifetime
  7. "Declining Quality" — the quality of an E-type system will appear to be declining unless it is rigorously maintained and adapted to operational environment changes
  8. "Feedback System" — E-type evolution processes constitute multi-level, multi-loop, multi-agent feedback systems and must be treated as such to achieve significant improvement over any reasonable base
It is worth mentioning that the applicability of all of these laws for all types of software systems has been studied by several researchers. For example, see a presentation by Nanjangud C Narendra where he describes a case study of an enterprise Agile project in the light of Lehman’s laws of software evolution. Some empirical observations coming from the study of open source software development appear to challenge some of the laws.
The laws predict that the need for functional change in a software system is inevitable, and not a consequence of incomplete or incorrect analysis of requirements or bad programming. They state that there are limits to what a software development team can achieve in terms of safely implementing changes and new functionality.
Maturity Models specific to software evolution have been developed to improve processes, and help to ensure continuous rejuvenation of the software as it evolves iteratively.
The "global process" that is made by the many stakeholders has many feedback loops. The evolution speed is a function of the feedback loop structure and other characteristics of the global system. Process simulation techniques, such as system dynamics can be useful in understanding and managing such global process.
Software evolution is not likely to be Darwinian, Lamarckian or Baldwinian, but an important phenomenon on its own. Given the increasing dependence on software at all levels of society and economy, the successful evolution of software is becoming increasingly critical. This is an important topic of research that hasn't received much attention.
The evolution of software, because of its rapid path in comparison to other man-made entities, was seen by Lehman as the "fruit fly" of the study of the evolution of artificial systems.

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