The Semantic Web Rule Language (SWRL) is a proposed language for the Semantic Web that can be used to express rules as well as logic, combining OWL DL or OWL Lite with a subset of the Rule Markup Language (itself a subset of

Datalog Datalog is a declarative logic programming language. While it is syntactically a subset of Prolog, Datalog generally uses a bottom-up rather than top-down evaluation model. This difference yields significantly different behavior and properties ...

). The specification was submitted in May 2004 to the W3C by the

National Research Council of Canada The National Research Council Canada (NRC; french: Conseil national de recherches Canada) is the primary national agency of the Government of Canada dedicated to science and technology research & development. It is the largest federal research ...

, Network Inference (since acquired by webMethods), and Stanford University in association with the Joint US/EU ad hoc Agent Markup Language Committee. The specification was based on an earlier proposal for an OWL rules language. SWRL has the full power of OWL DL, but at the price of decidability and practical implementations. However, decidability can be regained by restricting the form of admissible rules, typically by imposing a suitable safety condition. Rules are of the form of an implication between an antecedent (body) and consequent (head). The intended meaning can be read as: whenever the conditions specified in the antecedent hold, then the conditions specified in the consequent must also hold.

Example

Human Readable Syntax

hasParent(?x1,?x2) ∧ hasBrother(?x2,?x3) ⇒ hasUncle(?x1,?x3)

XML Concrete Syntax

The

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. ...

Concrete Syntax is a combination of the ''OWL Web Ontology Language XML Presentation Syntax'' with the ''RuleML XML syntax''. x1 x2 x2 x3 x1 x3

RDF Concrete Syntax

It is straightforward to provide such an RDF concrete syntax for rules, but the presence of variables in rules goes beyond the RDF Semantics. Translation from the XML Concrete Syntax to RDF/XML could be easily accomplished by extending the

XSLT XSLT (Extensible Stylesheet Language Transformations) is a language originally designed for transforming XML documents into other XML documents, or other formats such as HTML for web pages, plain text or XSL Formatting Objects, which may subse ...

transformation for the OWL XML Presentation syntax.

Implementations

Caveat: Reasoners do not support the full specification because the reasoning becomes undecidable. There can be three types of approach: # translate SWRL into First Order Logic (Hoolet) and demonstrate reasoning tasks with a theorem prover; # translate OWL-DL into rules and give the rules to a forward chaining engine (Bossam) (this approach cannot cover the full expressivity of OWL-DL due to many incompatibilities between Description Logic and Horn Rule formalisms) # expand an existing OWL-DL reasoner based on the tableaux algorithm (Pellet). * Protégé 4.2 includes a Rules view in its Ontology Views that supports SWRL rules. * For older versions of Protégé, SWRLTab is an extension that supports editing and execution of SWRL rules

*

R2ML The REWERSE Rule Markup Language (R2ML) is developed by thREWERSE Working Group I1for the purpose of rules interchange between different systems and tools. Scope * An XML based rule language; * Support for: integrity rules, derivation rules, prod ...

(REWERSE Rule Markup Language) supports SWRL

* Bossam, a forward chaining rule engine supports SWRL

* Hoolet, an implementation of an OWL-DL reasoner that uses a first order prover supports SWRL

* Pellet, an open-source Java OWL DL reasoner has SWRL-support

* KAON2 is an infrastructure for managing OWL-DL, SWRL, and F-Logic ontologies

* RacerPro, supports processing of rules in a SWRL-based syntax by translating them into nRQL rule

* RDFox a high-performance In-memory database, in-memory scalable knowledge graph and Datalog reasoning engine that supports OWL 2RL and SWRL. Developed by Oxford Semantic Technologies

* Stardog is an RDF database or triplestore that rewrites queries to answer questions using SWRL inferences

Comparison with Description Logic Programs

Description Logic Programs Description is the pattern of narrative development that aims to make vivid a place, object, character, or group. Description is one of four rhetorical modes (also known as ''modes of discourse''), along with exposition, argumentation, and na ...

(DLPs) are another proposal for integrating rules and OWL. Compared with Description Logic Programs, SWRL takes a diametrically opposed integration approach. DLP is the intersection of Horn logic and OWL, whereas SWRL is (roughly) the union of them. In DLP, the resultant language is a very peculiar looking description logic and rather inexpressive language overall.

References

External links

SWRL: A Semantic Web Rule Language Combining OWL and RuleML
W3C Member Submission 21 May 2004
A Proposal for a SWRL Extension towards First-Order Logic
W3C Member Submission 11 April 2005
OWL Web Ontology Language XML Presentation Syntax
W3C Note 11 June 2003 {{Semantic Web Semantic Web Knowledge representation languages