Regular Queries on Graph Databases

Abstract

Graph databases are currently one of the most popular paradigms for storing data. One of the key conceptual differences between graph and relational databases is the focus on navigational queries that ask whether some nodes are connected by paths satisfying certain restrictions. This focus has driven the definition of several different query languages and the subsequent study of their fundamental properties.We define the graph query language of Regular Queries, which is a natural extension of unions of conjunctive 2-way regular path queries (UC2RPQs) and unions of conjunctive nested 2-way regular path queries (UCN2RPQs). Regular queries allow expressing complex regular patterns between nodes. We formalize regular queries as nonrecursive Datalog programs with transitive closure rules. This language has been previously considered, but its algorithmic properties are not well understood.Our main contribution is to show elementary tight bounds for the containment problem for regular queries. Specifically, we show that this problem is 2Expspace-complete. For all extensions of regular queries known to date, the containment problem turns out to be nonelementary. Together with the fact that evaluating regular queries is not harder than evaluating UCN2RPQs, our results show that regular queries achieve a good balance between expressiveness and complexity, and constitute a well-behaved class that deserves further investigation.

Certified Graph View Maintenance with Regular Datalog

“…In this section, we present the theory of Regular Datalog (RD) and its Coq mechanization. The language is based on Regular Queries (RQs) (Reutter et al 2017). In Sec.…”

“…Their common denominator is that they perform edge traversals (through join chains), while specifying and testing for the existence of label-constrained paths. Recently, a solution to the long standing open problem of identifying a suitable graph query Datalog fragment, balancing expressivity and tractability, has been proposed in (Reutter et al 2017). We call this Regular Datalog (RD), a binary linear Datalog subclass that allows for complex, regular expression patterns between nodes.…”

Reasoning Web. Web Logic Rules

“…Query containment of Datalog queries is known to be undecidable [198], while this problem has been shown decidable even for extensions of C2RPQs [44,55,84,180] and in the presence of constraints [61,99]. Take for example the fundamental analysis task of query containment, which consists in deciding whether the answer to one query is always contained in the answer to another query over every possible database.…”

“…The issue of defining interesting path query languages that support nesting remains an active area of research in the database community, and there have been several recent proposals, including: regular queries [180], guarded regular queries [33], nested monadically defined queries [192], and the more general family of nested flag-and-check queries [44]. Beyond nesting and negation, (C)2RPQs have also been extended with path variables and regular relations [21].…”

Context-free path querying with structural representation of result

“…Despite the fact that there is a set of path querying solutions [18,9,4,13], query result exploration is still a challenge [10], as also a simplification of complex query debugging. Structural representation of query result can be used to solve these problems, and classical parsing techniques provide such representation-derivation tree-which contains exhaustive information about parsed sentence structure in terms of specified grammar.…”