The OWL Abstract Syntax and Semantics (AS&S) document provides a characterisation of OWL ontologies in terms of an abstract syntax. This is a high level description of the way in which we can define the characteristics of classes and properties.
In addition, AS&S gives a mapping to RDF triples. This tells us how such an abstract description of an OWL ontology can be transformed to a collection of RDF triples (which can then be represented in a concrete fashion using, for example RDF-XML).
In order to parse an OWL-RDF file into some structure closer to the abstract syntax we need to reverse this mapping, i.e. determine what the class definitions were that lead to those particular triples. Note that this reverse mapping is not necessarily unique, but for the purposes of validation we are simply interested in whether such a reverse mapping exists.
An arbitrary RDF graph may not necessarily correspond to an OWL [Lite|DL] ontology. In other words, there may not be an OWL [Lite|DL] ontology which when transformed using the mapping produces the given graph. This is what the species validator attempts to determine: if such a graph exists.
There are, in general, two ways in which an RDF graph may fail to correspond to an OWL [Lite|DL] ontology.
We can loosely describe the first as syntactic errors, and the second as semantic errors. Examples of syntactic errors include:
owl:Class
context
(e.g. as the object of an owl:someValuesFrom
property
whose subject is an owl:Restriction
which has an
owl:onProperty
property with an
owl:ObjectProperty
as its object) without explicitly
including a statement that the URI reference is an
owl:Class
or owl:Restriction
. The AS&S
requires that all such usages are given an explicit typing. owl:Restriction
, e.g. missing an
owl:onProperty
property.rdf:Property
instead
of the more specific owl:ObjectProperty
and
owl:DatatypeProperty
.Once we have an ontology in abstract form, there are a number of conditions that must hold in order for the ontology to be a member of the OWL [Lite|DL] subspecies. For example, there are restrictions on the expressiveness that can be used in OWL Lite (no unions or enumerations and limited cardinality restrictions). The Lite and DL subspecies also have a constraint that effectively says that the collections of URI references of classes, individuals and properties must be disjoint. Thus in OWL Lite and DL we can not use metamodelling devices such as classes as instances.
The validator will report on any violations of either syntactic or semantic constraints. Those things which it considers are RDF related (malformed syntax or missing type information) will be reported as such.