An Integrated Information System Powered by Prolog

摘要

Our Faculty embarked a few years ago on an ambitious project to redesign itself around an integrated information system, aimed at supporting all information handling activities and deployed through dynamic Web interfaces automatically customized for individual users. The project includes both the design of the services and the development of appropriate software technology to implement them. It led already to a running system, supporting many official academic procedures, which is under constant evolution. The system architecture is fully based on Prolog, connected to an external database engine. This paper summarizes and discusses the characteristics that make Prolog a vehicle of choice for the implementation, along with a sketch of main aspects of the system architecture and the specific declarative techniques that were developed for them. The recurring methodological gain is the ease of building abstraction layers supported by specific term sub-languages, due to the combination of flexible operator syntax with the power of the underlying machinery to define new constructs. The basic programming layer evolved from standard Prolog to a novel structured version of it, with compositional semantics (no cuts) and direct support for structural abstraction and application, combining in practice the logic programming style with the higher-order power and some of the programming flavour of functional languages. The system's main architectural glue is the conceptual scheme, for which a definition language was developed whose expressions are compiled (by Prolog) to induce the database tables and (the instantiation of) a query/update language with a syntax based on compositionality principles of natural language, whose expressions are both more natural and much more compact than the equivalent in SQL.