Semantic Web Rule Language

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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).[1]

The specification was submitted in May 2004 to the

National Research Council of Canada, 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.[2][3]

SWRL has the full power of OWL DL, but at the price of decidability and practical implementations.[4] However, decidability can be regained by restricting the form of admissible rules, typically by imposing a suitable safety condition.[5]

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

 <ruleml:imp> 
  <ruleml:_rlab ruleml:href="#example1"/>
  <ruleml:_body> 
    <swrlx:individualPropertyAtom  swrlx:property="hasParent"> 
      <ruleml:var>x1</ruleml:var>
      <ruleml:var>x2</ruleml:var>
    </swrlx:individualPropertyAtom> 
    <swrlx:individualPropertyAtom  swrlx:property="hasBrother"> 
      <ruleml:var>x2</ruleml:var>
      <ruleml:var>x3</ruleml:var>
    </swrlx:individualPropertyAtom> 
  </ruleml:_body> 
  <ruleml:_head> 
    <swrlx:individualPropertyAtom  swrlx:property="hasUncle"> 
      <ruleml:var>x1</ruleml:var>
      <ruleml:var>x3</ruleml:var>
    </swrlx:individualPropertyAtom> 
  </ruleml:_head> 
 </ruleml:imp>

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.[6] Translation from the XML Concrete Syntax to RDF/XML could be easily accomplished by extending the 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:

  1. translate SWRL into First Order Logic (Hoolet) and demonstrate reasoning tasks with a theorem prover;
  2. 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)
  3. 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. [1]
  • R2ML (REWERSE Rule Markup Language) supports SWRL. [2]
  • Bossam, a forward chaining rule engine supports SWRL. [3]
  • Hoolet, an implementation of an OWL-DL reasoner that uses a first order prover supports SWRL. [4]
  • Pellet, an open-source Java OWL DL reasoner has SWRL-support. [5]
  • KAON2 is an infrastructure for managing OWL-DL, SWRL, and F-Logic ontologies. [6]
  • RacerPro, supports processing of rules in a SWRL-based syntax by translating them into nRQL rules [7]
  • Stardog is an RDF database or triplestore that rewrites queries to answer questions using SWRL inferences. [8]
Bossam Hoolet Pellet
SWRL/OWLX Parser Yes ? ?
SWRL/RDF Parser Yes ? Yes
Math Built-Ins Partial ? Yes
String Built-Ins Partial ? Yes
Comparison Built-Ins ? ? Yes
Boolean Built-Ins ? ? Yes
Date, Time and Duration Built-Ins ? ? No
URI Built-Ins ? ? Yes
Lists Built-Ins ? ? No
Licensing Free/closed-source Free/open-source Free/open-source

Comparison with Description Logic Programs

Description Logic Programs (DLPs) are another proposal for integrating rules and OWL.[7] 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.[4] In DLP, the resultant language is a very peculiar looking description logic and rather inexpressive language overall.[4]

See also

References

  1. ^ "SWRL: A Semantic Web Rule Language Combining OWL and RuleML". w3.org. Retrieved 21 December 2017.
  2. ^ Ian Horrocks; Peter F. Patel-Schneider (2004). "A Proposal for an OWL Rules Language" (PDF). Proc. of the Thirteenth International World Wide Web Conference (WWW 2004). ACM. pp. 723–731. Retrieved 22 May 2014.
  3. doi:10.1016/j.websem.2005.05.003
    . Retrieved 22 May 2014.
  4. ^ a b c Bijan Parsia; et al. (2005). "Cautiously Approaching SWRL" (PDF). Retrieved 29 July 2006. {{cite journal}}: Cite journal requires |journal= (help)
  5. doi:10.1016/j.websem.2005.05.001
    . Retrieved 22 May 2014.
  6. S2CID 14325289
    . Retrieved 29 July 2006.
  7. ^ Benjamin N. Grosof; Ian Horrocks; Raphael Volz; Stefan Decker (2003). "Description Logic Programs: Combining Logic Programs with Description Logic" (PDF). Proc. of the Twelfth International World Wide Web Conference (WWW 2003). ACM. pp. 48–57. Retrieved 22 May 2014.

External links

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