Our experimental analysis of several popular XPath processors reveals a striking fact: Query evaluation in each of the systems requires time exponential in the size of queries in the worst case.Expand

We show that both the data complexity and query complexity of XPath 1.0 fall into lower (highly parallelizable) complexity classes, but that the combined complexity is PTIME-hard.Expand

We propose a tree representation for SPARQL queries, called pattern trees, which captures the class of well-designed graph patterns and which can be considered as a query execution plan.Expand

We show that virtually all relevant decision problems in the area of abduction, closed world reasoning, circumscription, and disjunctive logic programming become tractable if the treewidth of the graphs is bounded by a fixed constant.Expand

We introduce expressive identification constraints to capture functional dependencies and define an RDF Normal Form, which precisely captures the classical Boyce-Codd Normal Form of relational schemas.Expand

We study the query complexity and combined complexity of tuple generating dependencies (tgds) which enforce the presence of certain tuples in a database instance if certain other tuples are already present.Expand

We propose monadic datalog (i.e., data log where all intentional predicate symbols are unary) as an alternative method to tackle this class of fixed-parameter tractable problems.Expand