Querying Data Graphs with Arithmetical Regular Expressions.

We propose a query language LARE for graphs whose edges are labelled by a finite alphabet and nodes store unbounded data values. LARE is based on a variant of regular expressions with memory. Queries of LARE can compare quantities of memorised graph nodes and their neighbourhoods. These features allow us to express a number of natural properties, while keeping the data complexity (with a query fixed) in non-deterministic logarithmic space. We establish an algorithm that works efficiently not only with LARE, but also with a wider language defined using effective relational conditions, another formalism we propose.