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Complexity of conjunctive regular path query homomorphisms. (English) Zbl 1434.68139

Manea, Florin (ed.) et al., Computing with foresight and industry. 15th conference on computability in Europe, CiE 2019, Durham, UK, July 15–19, 2019. Proceedings. Cham: Springer. Lect. Notes Comput. Sci. 11558, 108-119 (2019).
Summary: A graph database is a digraph whose arcs are labelled with symbols from a fixed alphabet. A regular graph pattern (RGP) is a digraph whose edges are labelled with regular expressions over the alphabet. RGPs model navigational queries for graph databases, more precisely, conjunctive regular path queries. A match of a navigational RGP query in the database is witnessed by a special navigational homomorphism of the RGP to the database. We study the complexity of deciding the existence of a homomorphism between two RGPs. Such homomorphisms model a strong type of containment between two navigational RGP queries. We show that this problem can be solved by an EXPTIME algorithm (while general query containment in this context is EXPSPACE-complete). We also study the problem for restricted RGPs over a unary alphabet, that arise from some applications like XPath, and prove that certain interesting cases are polynomial-time solvable.
For the entire collection see [Zbl 1428.68037].

MSC:

68P15 Database theory
68Q25 Analysis of algorithms and problem complexity
68R10 Graph theory (including graph drawing) in computer science
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