Reasoning-aware, format versatile Web querying that makes querying as easy as creating data

RDFS Reasoning in Xcerpt

RDFS entailment (or reasoning) in Xcerpt is provided by a set of rules described in the following. In 2004/2005 we started to work on a better integration of RDF into Xcerpt. Xcerpt has been conceived from the very beginning as a versatile query language capable of accessing any form of semi-structured data. However, in practice each format has its own, specific challenges.

In the case of RDF, our first step to supporting RDF in Xcerpt has been twofold:

  1. Provide Xcerpt rule libraries that can parse and "normalize" RDF data into canonical Xcerpt representations, see [rdf-normalization-and-parsing-in-xcerpt];
  2. Provide Xcerpt rule libraries that handle specificities of the RDF semantics, i.e., that (transparently) extend the RDF graph in accordance to the RDF(S) entailment rules from the RDF model theory.

For details on how these rules are constructed and what shortcomings they have, please refer to Oliver Bolzer's master thesis on RDF access in Xcerpt.

All files pertaining to this application of Xcerpt can be found at http://svn.amachos.com/xcerpt/applications/2004/rdfs-reasoning/. Feel free to access them using any browser or to check them out with any Subversion client.

It might be useful to keep the following points in mind when looking at the Xcerpt program:

  • First, as described in Oliver Bolzer's master thesis these rules are manually "stratified" to ensure termination, i.e., they need to be put into strata such that RDF triples generate in upper strata do not affect lower strata. Thus, the n-th stratum provides the grounding for the n+1-th stratum.
  • Second, these rules use 2004 Xcerpt syntax which differs quite noticably from the current Xcerpt syntax described in Deliverable D6.
  • Third, the representation of RDF in Xcerpt is, admittedly, suboptimal. The goal for this rules was to get them working in the 2004 Xcerpt prototype and this required certain compromises. We are currently working on a better representation and processing of RDF in Xcerpt, please contact Benedikt Linse for more information.