A Non-Deterministic Multiset Query Language
This work addresses the need for flexible querying in business process simulation, though it appears incremental as it builds on existing term rewriting and relational algebra concepts.
The authors developed a non-deterministic multiset query language for modeling user choices in data-centric business processes, proving it can express any relational algebra query and implementing it in Maude.
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.