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The OWL 2 RL profile is aimed at applications that require scalable reasoning without sacrificing too much expressive power. It is designed to accommodate both OWL 2 applications that can trade the full expressivity of the language for efficiency, and RDF(S) applications that need some added expressivity from OWL 2. This is achieved by defining a syntactic subset of OWL 2 which is amenable to implementation using rule-based technologies, and presenting a partial axiomatization of the OWL 2 semantics in the form of first-order implications that can be used as the basis for such an implementation.
Suitable rule-based implementations of OWL 2 RL under RDF-Based Semantics can be used with arbitrary RDF graphs. As a consequence, OWL 2 RL is ideal for enriching RDF data, especially when the data must be massaged by additional rules. From a modeling perspective, however, this pushes us farther away from working with class expressions: OWL 2 RL ensures we cannot (easily) talk about unknown individuals in our superclass expressions (this restriction follows from the nature of rules). Compared with OWL 2 QL, OWL 2 RL works better when you have already massaged your data into RDF and are working with it as RDF.
Among other constructs, OWL 2 RL disallows statements where the existence of an individual enforces the existence of another individual: for instance, the statement “every person has a parent” is not expressible in OWL RL.
OWL 2 RL restricts class axioms asymmetrically, that is, you can use constructs as the subclass that you cannot use as the superclass.
The RL acronym reflects the fact that reasoning in this profile can be implemented using a standard Rule Language [DLP].
The following is an example which uses some of the typical modeling features available in OWL 2 RL. The first – somewhat contrived – axiom states that for each of Mary, Bill, and Meg who is female, the following holds: she is a parent with at most one child, and all her children (if she has any) are female.
Functional-Style Syntax
 SubClassOf(
   ObjectIntersectionOf(
     ObjectOneOf( :Mary :Bill :Meg )
     :Female
   )
   ObjectIntersectionOf(
     :Parent
     ObjectMaxCardinality( 1 :hasChild )
     ObjectAllValuesFrom( :hasChild :Female )
   )
 )
 
 DisjointClasses( 
   :Mother 
   :Father 
   :YoungChild 
 )
 
 SubObjectPropertyOf( 
   ObjectPropertyChain( :hasFather :hasBrother ) 
   :hasUncle 
 )