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
webMethods was an enterprise software company focused on application integration, business process integration and B2B partner integration. Founded in 1996, the company sold systems for organizations to use web services to connect software app ...
), 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.
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''.
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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
RDF/XML is a syntax,RDF/XML Syntax Specification XSLT 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 (REWERSE Rule Markup Language) supports SWRL * Bossam, a
forward chaining
Forward chaining (or forward reasoning) is one of the two main methods of reasoning when using an inference engine and can be described logically as repeated application of ''modus ponens''. Forward chaining is a popular implementation strategy ...
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
The Google Knowledge Graph is a knowledge base from which Google serves relevant information in an infobox beside its search results. This allows the user to see the answer in a glance. The data is generated automatically from a variety of sou ...
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 (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.
Web Ontology Language
The Web Ontology Language (OWL) is a family of knowledge representation languages for authoring ontologies. Ontologies are a formal way to describe taxonomies and classification networks, essentially defining the structure of knowledge for vario ...
- "OWL"
*
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 ...
Semantic wiki
A semantic wiki is a wiki that has an underlying model of the knowledge described in its pages. Regular, or syntactic, wikis have structured text and untyped hyperlinks. Semantic wikis, on the other hand, provide the ability to capture or identif ...