Towards Query Optimization for SPARQL Property Paths

The extension of SPARQL in version 1.1 with property paths offers a type of regular path query for RDF graph databases. Such queries are difficult to optimize and evaluate efficiently, however. We have embarked on a project, Waveguide, to build a cost-based optimizer for SPARQL queries with property paths. Waveguide builds a query plan - a waveguide plan (WGP) - which guides the query evaluation. There are numerous choices in the construction of a plan, and a number of optimization methods, meaning the space of plans for a query can be quite large. Execution costs of plans for the same query can vary by orders of magnitude. We illustrate the types of optimizations this approach affords and the performance gains that can be obtained. A WGP's costs can be estimated, which opens the way to cost-based optimization

A Cost-based Optimizer for SPARQL Queries

The cost of answering a query against an ontology is affected by at least three elements: the size of the ontology, the strategy followed to combine the data, and the order or plan in which data is processed. In the context of the Semantic Web, very large ontologies have been defined; therefore, techniques to identif