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Representing Paths in Graph Database Pattern Matching

Modern graph database query languages such as GQL, SQL/PGQ, and their academic predecessor G-Core promote paths to first-class citizens in the sense that paths that match regular path queries can be returned to the user. This brings a number of challenges in terms of efficiency, caused by the fact that graphs can have a huge amount of paths between a given node pair. We introduce the concept of path multiset representations (PMRs), which can represent multisets of paths in an exponentially succinct manner. After exploring fundamental problems such as minimization and equivalence testing of PMRs, we explore how their use can lead to significant time and space savings when executing query plans. We show that, from a computational complexity point of view, PMRs seem especially well-suited for representing results of regular path queries and extensions thereof involving counting, random sampling, unions, and joins.