Querying graph databases: What do graph patterns mean?

Abstract

Querying graph databases often amounts to some form of graph pattern matching. Finding (sub-)graphs isomorphic to a given graph pattern is common to many graph query languages, even though graph isomorphism often is too strict, since it requires a one-to-one correspondence between the nodes of the pattern and that of a match. We investigate the influence of weaker graph pattern matching relations on the respective queries they express. Thereby, these relations abstract from the concrete graph topology to different degrees. An extension of relation sequences, called failures which we borrow from studies on concurrent processes, naturally expresses simple presence conditions for relations and properties. This is very useful in application scenarios dealing with databases with a notion of data completeness. Furthermore, failures open up the query modeling for more intricate matching relations directly incorporating concrete data values.