A Non-Deterministic Multiset Query Language

TL;DR

This paper introduces a non-deterministic multiset query language designed for flexible data modeling and analysis, implemented via term rewriting and capable of expressing relational algebra queries.

Contribution

It presents a novel non-deterministic query language with unique quantification and fresh value introduction, implemented in Maude, for modeling complex data interactions.

Findings

Language can express any relational algebra query

Query evaluation is implemented through term rewriting and normalization

Non-determinism aids in modeling user choices and reachability analysis

Abstract

We develop a multiset query and update language executable in a term rewriting system. Its most remarkable feature, besides non-standard approach to quantification and introduction of fresh values, is non-determinism - a query result is not uniquely determined by the database. We argue that this feature is very useful, e.g., in modelling user choices during simulation or reachability analysis of a data-centric business process - the intended application of our work. Query evaluation is implemented by converting the query into a terminating term rewriting system and normalizing the initial term which encapsulates the current database. A normal form encapsulates a query result. We prove that our language can express any relational algebra query. Finally, we present a simple business process specification framework (and an example specification). Both syntax and semantics of our query language is implemented in Maude.