On 12/13/2011 01:51 PM, Stephen Bayliss wrote:
In ECM, the type of an object is defined effectively from its CModel.
One can validate the type of the target of a relationship, the typing
being specified by the hasModel relationship.
Is it possible to do any additional type validation; eg if I want to
enforce that all objects "belonging" to the CModel must assert an
rdf:type relationship?
Sure, specify the minCardinality for the rdf:type relation. That way,
all subscribing objects must have an rdf:type relationship.
I've tried adding an owl:Restriction on the rdf:type relationship
using owl:hasValue to specify the value of the target (rather than its
class) - but this doesn't look as if it is implemented.
http://www.w3.org/TR/owl-ref/#hasValue-def
NOTE: the value constraint|owl:hasValue|is not included in OWL Lite.
I've also tried using an owl:Restriction on a hasMember relationship;
instead of specifying the target's CModel class I used a value that
the target is itself asserting using rdf:type, but it doesn't lok like
this is tested for.
rdf:type is a sore point for OWL. Fedora CMA does not concern itself
with rdf:type. A fedora object is NOT "of a type" just because it
subscribe to a content model.
Now, one could define
fedora:hasModel isSubtypeOf rdf:type
The problem here is that, to owl, fedora:hasModel is an
owl:ObjectProperty and rdf:type is a rdf:Property. To make the above
statement understandable to a reasoner, you would need owl full.
For the purpose of ECM, i defined that
object fedora:hasModel contentmodel creates a phony rdf property
object rdf:type contentmodel#class
This property is, of course, not added to the triple store.
Remember that it does require owl full, if a content model should be
both an object and a class. That is why we use contentmodel#class for
the rdf:type information.
So a question, is ECM relationships validation restricted to:
1) checking the cardinality of a relationship
2) checking the type of the target of a relationship where the type is
specified using hasModel
Is there anything one can do for enforcing rdf:type assertions?
writing a schema for the RELS-EXT datastream?
<xsd:schema
attributeFormDefault="qualified"
elementFormDefault="qualified"
targetNamespace="http://www.w3.org/1999/02/22-rdf-syntax-ns#";
xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#";
xmlns:xsd="http://www.w3.org/2001/XMLSchema";>
<xsd:element name="RDF">
<xsd:complexType>
<xsd:sequence>
<xsd:element minOccurs="1"maxOccurs="1"name="Description">
<xsd:complexType mixed="true">
<xsd:sequence minOccurs="0"maxOccurs="unbounded">
<xsd:any processContents="lax"/>
<!-- Insert required element here...-->
</xsd:sequence>
<xsd:attribute name="about"type="xsd:anyURI"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
But on a more serious note, no, there isn't. To do this right, we need
1. To define the implied relation between fedora:hasModel and rdf:type
2a. Find an apache-licensed reasoner, that support more than owl-lite
(or switch fedora to gpl3, and use pellet)
2b/ Or: choose to support some subset of owl full/DL specification, and
thus in effect, make our own dialect of owl.
Regards
(Though I realise in practice, with reasoning support, one would make
a statement about the CModel#class that it is eg a subtype, or
owl:sameAs etc).
Thanks
Seve
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