OR-SML: A Functional Database Programming Language for Disjunctive Information

We describe a functional database language OR-SML for handling disjunctive information in database queries, and its implementation on top of Standard ML. The core language has the power of the nested relational algebra, and it is augmented with or-sets which are used to deal with disjunctive information. Sets, or-sets and tuples can be freely combined to create objects, which gives the language a greater flexibility. We give examples of queries which require disjunctive information (such as querying incomplete or independent databases) and show how to use the language to answer these queries. Since the system runs on top of Standard ML and all database objects are values in the latter, the system benefits from combining a sophisticated query language with the full power of a programming language. OR-SML includes a number of primitives that deal with bags and aggregate functions. It is also configurable by user-defined base types. The language has been implemented as a library of modules in Standard ML. This allows the user to build just the database language as an independent system, or to interface it to other systems built in Standard ML. We give an example of connecting OR-SML with an already existing interactive theorem prover.