5GL

5GL stands for fifth-generation programming languages, a label used in the 1980s and 1990s to describe a class of programming environments designed to enable software creation by specifying the problem and its constraints rather than detailing step-by-step algorithms. Proponents envisioned languages and systems capable of automatic code generation through inference, knowledge representation, and natural language interfaces, often built on AI techniques such as rule-based systems, logic programming, and constraint solving.

Characteristics of 5GLs emphasize declarative programming, domain-specific or knowledge-based approaches, and the use of inference engines or constraint solvers. They aim to let users specify what is required rather than how to compute it, potentially enabling programming by example or natural language interaction. These systems often integrate with databases and knowledge bases and rely on AI techniques to derive solutions from high-level specifications.

History and status: the Japanese Fifth Generation Computer Systems project popularized the term and influenced research into AI, logic programming, and knowledge-based systems. Early tools such as OPS5 and Prolog are frequently cited in discussions of 5GLs, but these are usually classified within AI and declarative programming traditions rather than as a unified modern generation. The concept of a distinct fifth generation did not become a widely adopted practical paradigm, with attention shifting to 4GLs, domain-specific languages, low-code platforms, and AI-assisted development.

Legacy: the 5GL idea contributed to ongoing work in declarative programming, knowledge representation, and AI planning. Today, discussions about declarative approaches and natural language interfaces in software development reflect some of the goals once associated with 5GLs, even as the category itself remains largely historical.