View source for ShEx/Obsolete/ShEx vs OWL

<p style="background-color: #fdd;  font-size: 2em"><span style="color:#F00;">Obsolete</span> - please see [http://shex.io/shex-primer/#relationship ShEx Primer]</p>

== ShEx vs OWL ==

The main difference is that OWL is tailored to describe a domain while Shape Expressions are tailored to describe RDF graphs. The domain of discourse of OWL is more related to the problem domain in which one is working like people, organizations, etc. while the domain of discourse of Shape Expressions is the RDF graph that one is trying to describe. 

Apart from that, OWL is based on Open World Assumption and Non-Unique Name Assumption while Shape Expressions employ a Closed World and Unique Name assumption. This feature makes more difficult to use OWL as a constraint validation language as has been documented, for example, in [http://www.cs.rpi.edu/~taoj2/2010/iswc2010dc.pdf this paper].

As a simple example, we can try to express the Shape:

 :UserShape {  foaf:name xsd:string
            |  foaf:givenName xsd:string+, foaf:familyName xsd:string
 }

which means that a <code>:UserShape</code> has either exactly one <code>foaf:name</code>, or a combination
of one or more <code>foaf:giveName</code> and exactly one <code>foaf:fammilyName</code>

If we have:

 :mary foaf:name "Mary Smith" .
 
 :john foaf:givenName "john" ; foaf:givenName "johnny" ;
       foaf:familyName "Smith" .

A Shape Expressions processor infers that <code>:mary</code> and <code>:john</code> have shape <code>:UserShape</code>. 

But if we have:

 :mary2 foaf:name "Mary1" , "Mary2" .
 :john2 foaf:givenName "john"; foaf:familyName 2 .

the system will not infer that <code>mary2</code> or <code>john2</code> have <code>:UserShape</code> [http://rdfshape.herokuapp.com/validator?rdf=prefix+%3A+%3Chttp%3A%2F%2Fexample.org%2F%3E%0D%0Aprefix+foaf%3A+%3Chttp%3A%2F%2Fxmlns.com%2Ffoaf%2F0.1%2F%3E%0D%0A%0D%0A%3Amary+foaf%3Aname+%22Mary+Smith%22+.%0D%0A%0D%0A%3Ajohn+foaf%3AgivenName+%22john%22+%3B+foaf%3AgivenName+%22johnny%22+%3B%0D%0A++++++foaf%3AfamilyName+%22Smith%22+.%0D%0A%0D%0A%3Amary2+foaf%3Aname+%22Mary1%22+%2C+%22Mary2%22+.%0D%0A%3Ajohn2+foaf%3AgivenName+%22john%22%3B+foaf%3AfamilyName+2+.&schema=prefix+%3A+%3Chttp%3A%2F%2Fexample.org%2F%3E%0D%0Aprefix+foaf%3A+%3Chttp%3A%2F%2Fxmlns.com%2Ffoaf%2F0.1%2F%3E%0D%0Aprefix+xsd%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F2001%2FXMLSchema%23%3E%0D%0A%0D%0A%3AUserShape+%7B++foaf%3Aname+xsd%3Astring%0D%0A+++++++++++%7C++foaf%3AgivenName+xsd%3Astring%2B%2C+foaf%3AfamilyName+xsd%3Astring%0D%0A%7D Try it].

In OWL we can express a class as the union of two other classes, so we could express <code>UserShapeClass</code>:

 :UserShapeClass owl:equivalentClass [
   rdf:type owl:Class ;
   owl:unionOf ( 
     :HasNameClass
     :HasGivenNameFamilyNameClass
   )
 ] .

and then, we can express <code>:HasNameClass</code> as:

 :HasNameClass owl:equivalentClass [
  a owl:Class ;
  owl:intersectionOf (
   [ rdf:type owl:Restriction ;
     owl:onProperty foaf:name ;
     owl:someValuesFrom xsd:string ;
   ] 
   [ rdf:type owl:Restriction ;
     owl:onProperty foaf:name ;
     owl:cardinality 1
   ] 
  )
 ] .

In the previous definition we declare that <code>:HasNameClass</code> has exactly one (cardinality = 1) <code>foaf:name</code> with type <code>xsd:string</code>. 

In the same way, we can declare <code>HasGivenNameFamilyNameClass</code> as:

 :HasGivenNameFamilyNameClass owl:equivalentClass [
  a owl:Class ;
  owl:intersectionOf  
   ([ rdf:type            owl:Restriction ;
      owl:onProperty      foaf:givenName ;
      owl:someValuesFrom  xsd:string 
    ] 
    [ rdf:type            owl:Restriction ;
      owl:onProperty      foaf:familyName ;
      owl:someValuesFrom  xsd:string 
    ] 
    [ rdf:type            owl:Restriction ;
      owl:onProperty      foaf:familyName ;
      owl:cardinality     1
    ]  
   )
  ] .

With the previous definitions, if we declare:

 :mary foaf:name "Mary Smith" .
 
 :johnSmith foaf:givenName "john" ;
            foaf:familyName "Smith" .

the system does not infer that <code>:mary</code> or <code>:johnSmith</code> belong to <code>:UserShapeClass</code>

In this case, this can be solved if we add:

 foaf:name a owl:FunctionalProperty .
 foaf:familyName a owl:FunctionalProperty .

which declares that one node does not have more than one value for propery <code>foaf:name</code> and <code>foaf:familyName</code>. Now, the declaration:

 :mary2 foaf:name "Mary1" , "Mary2" .

is detected as an inconsistency. If we remove the inconsistencies, the system infers that <code>:mary</code> and <code>:john</code> have type <code>:UserShapeClass</code>