# OWL compliance¶

GraphDB supports several OWL like dialects: OWL Horst (owl-horst), OWL Max (owl-max), which covers most of OWL Lite and RDFS, OWL2 QL (owl2-ql) and OWL2 RL (owl2-rl).

With the owl-max ruleset, GraphDB supports the following semantics:

• full RDFS semantics without constraints or limitations, apart from the entailment related to typed literals (known as D-entailment). For instance, meta-classes (and any arbitrary mixture of class, property, and individual) can be combined with the supported OWL semantics;
• most of OWL Lite;
• all of OWL DLP.

The differences between OWL Horst and the OWL dialects supported by GraphDB (owl-horst and owl-max) can be summarised as follows:

• GraphDB does not provide the extended support for typed literals, introduced with the D-entailment extension of the RDFS semantics. Although such support is conceptually clear and easy to implement, it is our understanding that the performance penalty is too high for most applications. You can easily implement the rules defined for this purpose by ter Horst and add them to a custom ruleset;
• There are no inconsistency rules by default;
• A few more OWL primitives are supported by GraphDB (ruleset owl-max);
• There is extended support for schema-level (T-Box) reasoning in GraphDB.

Even though the concrete rules pre-defined in GraphDB differ from those defined in OWL Horst, the complexity and decidability results reported for R-entailment are relevant for TRREE and GraphDB. To be more precise, the rules in the owl-horst ruleset do not introduce new B-Nodes, which means that R-entailment with respect to them takes polynomial time. In KR terms, this means that the owl-horst inference within GraphDB is tractable.

Inference using owl-horst is of a lesser complexity compared to other formalisms that combine DL formalisms with rules. In addition, it puts no constraints with respect to meta-modelling.

The correctness of the support for OWL semantics (for these primitives that are supported) is checked against the normative Positive- and Negative-entailment OWL test cases.