Declarative Programming and Knowledge Management

Most real-world applications inevitably face the issue of persistence, generally understood as how to design, maintain and interact with a database. The standard approach relies on the mature technology of relational databases, with interaction specified through SQL embedded in the host programming language. Attempts to raise the level of the error-prone interaction code have been in the direction of object-oriented databases or deductive databases, with simpler queries but less mature technology on the database part. Here we present a different high-level approach, close in spirit to natural language, using variable-free conceptual expressions that are quite concise, natural and easy to read and understand, promoting much better code maintenance than the alternative approaches. This is achieved by using the flexible operator syntax and the deductive capabilities of logic programming in two ways, first to compile the database scheme from a modular structural description into a clausal representation, and then to translate (using the compiled scheme) terms expressing queries and commands into SQL statements. The approach relies crucially on the use of attributes, whose inheritance and composition avoid many explicit joins. Expressions become natural by choosing the right noun phrases (rather than verbal) for the attributes. A useful feature is the use of global parameters for implicit current values. Our deductive handle on the scheme allows the query translation to automatically split the needed joins into inner and outer joins. The abstraction power is further raised by having manifold attributes, whose values actually vary along a parametric domain, the main examples being the handling of temporal and multi-lingual data. Commands can also be very high-level, for example the simple statement of update of an identity value (part of the primary key) of an individual results in its replacement in all tuples of all concepts where the individual was referenced, this being done in the correct order to prevent violation of foreign keys. We present the ideas incrementally, with examples along with a rigorous account of the used syntax and semantics.