In software engineering, the laws of software evolution refer to a series of laws that Lehman and Belady formulated starting in 1974 with respect to software evolution. The laws describe a balance between forces driving new developments on one hand, and forces that slow down progress on the other hand. Over the past decades the laws have been revised and extended several times.

Context

Observing that most software is subject to change in the course of its existence, the authors set out to determine laws that these changes will typically obey, or must obey for the software to survive. In his 1980 article, Lehman qualified the application of such laws by distinguishing between three categories of software: The laws are said to apply only to the last category of systems.

The laws

All told, eight laws were formulated:

Relevance of the Laws of Software Evolution in Modern Software Engineering

In the dynamic world of modern software engineering, the Laws of Software Evolution continue to hold a profound relevance. These laws, originally formulated by Lehman and Belady in the 1970s, provide enduring insights into the nature of software systems and their evolution. In today's software development landscape, where agility and adaptability are paramount, these laws serve as guiding principles. "Continuing Change" is a foundational concept, emphasizing that software must evolve continually to remain satisfactory. This aligns perfectly with agile development methodologies, where iterative updates and feature enhancements are the norm. "Increasing Complexity" is another key law that underscores the need for active management of complexity, particularly in large and long-lived software projects. As software systems grow, modern engineering practices such as modular design, microservices, and DevOps help control and reduce complexity, ensuring that software remains maintainable and scalable. The Laws of Software Evolution also find relevance in the context of DevOps and continuous integration/continuous deployment (CI/CD). In a DevOps-driven environment, the "Continuing Growth" law is exemplified as software features must be continually expanded to meet evolving user demands and maintain user satisfaction. The "Declining Quality" law is a stark reminder that software quality can deteriorate over time without rigorous maintenance, highlighting the importance of automated testing and quality assurance in modern software development. Furthermore, the "Feedback System" law reinforces the idea that software evolution is a feedback-driven process, with multiple loops and agents involved. This resonates with the emphasis on collaboration and feedback within DevOps practices, ensuring that software is developed, tested, and deployed with a focus on continuous improvement. In summary, the Laws of Software Evolution continue to guide software engineers in navigating the complexities of modern development, from agile methodologies to DevOps, helping them deliver robust, evolving software systems.