Software evolution is the term used in software engineering (specifically software maintenance) to refer to the process of developing software initially, then repeatedly updating it for various reasons.
Contents |
Fred Brooks, in his key book The Mythical Man-Month,[1] 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.
The aim of software evolution would be implementing (and revalidate) the possible major changes to the system without being able a priority to predict how user requirements will evolve [1]. The existing larger system is never complete and continues to evolve [2]. As it evolves, the complexity of the system will grow unless there is a better solution available to solve these issues. The main objectives of software evolution are ensuring the reliability and flexibility of the system. During the 20 years pasted, the lifespan of a system could be in average 6-10 years. However, recently found that a system should be evolved once few months to ensure it is compromised to the real-world environment. This is due to the rapid growth of World Wide Web and Internet Resources that make users easier to find related information. The idea of software evolution leads to open source development as anybody could download the source codes and hence modify it. The positive impact in this case is large amounts of new ideas would be discovered and generated that aims the system to have better improvement in variety choices. However, the negative impact is there is no copyright if a software product has been published as open source.
references 1.
2.
Changes in Software Evolution Models and Theories
Over time, software systems, programs as well as applications 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 changed as to adapt to the evolution of the future software. Software process and development are an ongoing experience that has a never-ending cycle. After going through learning and refinements, it is always an arguable issue when it comes to matter of efficiency and effectiveness of the programs. [aeddy; ref: Understanding Open Source Software Evolution Walt Scacchi Institute for Software Research]
E.B. Swanson initially identified three categories of maintenance: corrective, adaptive, and perfective. Four categories of software were then catalogued by Lientz and Swanson (1980) [2]. These have since been updated and normalized internationally in the ISO/IEC 14764:2006:[3]
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. (1999) and Chapin (2001), 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 (Kitchemham et al. (1999), Derider (2002), Vizcaíno 2003, Dias (2003), and Ruiz (2004)), which enrich the description of the many evolution activities.
Current trends and practices are projected forward using a new model of software evolution called the staged model [1]. 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 (Initial development, Evolution, Servicing, Phase-out, and Close-down).
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 (or observations) are known as Lehman's Laws, and there are eight of them:
It is worth mentioning that the laws are believed to apply mainly to monolithic, proprietary software. For example, some empirical observations coming from the study of open source software development appear to challenge some of the laws .
The laws predict that change is inevitable and not a consequence of bad programming and that there are limits to what a software evolution 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 (e.g. developers, users, their managers) 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.