Finite Models in RDF(S), with Datatypes

The details of reasoning in RDF [2] and RDFS [1] are generally well known. There is a model-theoretic semantics for RDF [3, 4] and there are sound and complete proof theories for RDF without datatypes [6]. However, the model-theoretic characteristics of RDF have been less studied, particularly when datatypes are added. We show that RDF reasoning can be performed by only considering finite models or pre-models, and sometimes only very small models need be considered. Ter Horst [6] does define Herbrand models for RDF and RDFS, providing the basis for some model-theoretic characteristics of RDF and RDFS, but he does not provide a full analysis of RDF datatypes, analyzing instead an incomplete semantics for datatypes that is easier to reason in. As well, the recent minor modifications to the semantics of RDF [4], while cleaning up some aspects of entailment in RDF, do make some technical changes that might appear to interfere with finite model-based reasoning in RDF. An analysis of finite models for RDF shows that the modified semantics does not introduce any unintended changes to reasoning in RDF. As well, it provides insights into the modeling strength of RDF, particularly when blank nodes are not present, and illustrates how finite datatypes interact with the rest of RDF.