1 Introduction

The core of the SWI-Prolog package semweb is an efficient main-memory RDF store written in C that is tightly integrated with Prolog. It provides a fully logical predicate rdf/3 to query the RDF store efficiently by using multiple (currently 9) indexes. In addition, SWI-Prolog provides libraries for reading and writing XML/RDF and Turtle and a library that provides persistency using a combination of efficient binary snapshots and journals.

Below, we describe a few usage scenarios that guides the current design of this Prolog-based RDF store.

Application prototyping platform

Bundled with ClioPatria, the store is an efficient platform for prototyping a wide range of semantic web applications. Prolog, connected to the main-memory based store is a productive platform for writing application logic that can be made available through the SPARQL endpoint of ClioPatria, using an application specific API (typically based on JSON or XML) or as an HTML based end-user application. Prolog is more versatile than SPARQL, allows composing of the logic from small building blocks and does not suffer from the Object-relational impedance mismatch.

Data integration

The SWI-Prolog store is optimized for entailment on the rdfs:subPropertyOf relation. The rdfs:subPropertyOf relation is crucial for integrating data from multiple sources while preserving the original richness of the sources because integration can be achieved by defining the native properties as sub-properties of properties from a unifying schema such as Dublin Core.

Dynamic data

This RDF store is one of the few stores that is primarily based on backward reasoning. The big advantage of backward reasoning is that it can much easier deal with changes to the database because it does not have to take care of propagating the consequences. Backward reasoning reduces storage requirements. The price is more reasoning during querying. In many scenarios the extra reasoning using a main memory will outperform the fetching the precomputed results from external storage.

Prototyping reasoning systems

Reasoning systems, not necessarily limited to entailment reasoning, can be prototyped efficiently on the Prolog based store. This includes `what-if' reasoning, which is supported by snapshot and transaction isolation. These features, together with the concurrent loading capabilities, make the platform well equiped to collect relevant data from large external stores for intensive reasoning. Finally, the TIPC package can be used to create networks of cooperating RDF based agents.

Streaming RDF

Transactions, snapshots, concurrent modifications and the database monitoring facilities (see rdf_monitor/2) make the platform well suited for prototyping systems that deal with streaming RDF data.