Proper OWL2 EL profile learning support

[LorenzBuehmann]

In OWL2 EL only the following constructs are supported(see http://www.w3.org/TR/owl2-profiles/#OWL_2_EL):

• existential quantification to a class expression (ObjectSomeValuesFrom) or a data range (DataSomeValuesFrom)
• existential quantification to an individual (ObjectHasValue) or a literal (DataHasValue)
• self-restriction (ObjectHasSelf)
• enumerations involving a single individual (ObjectOneOf) or a single literal (DataOneOf)
• intersection of classes (ObjectIntersectionOf) and data ranges (DataIntersectionOf)

The basic EL learning algorithm ELTL only supports a subset of the constructs above, i.e. everything seems to be correct. On the other hand, we should add support for DataSomeValuesFrom and DataHasValue.

A special case is (ELTL + disjunctive) which also uses disjunction of class expression, i.e. solution might not be fit to OWL2 EL. Moreover, support for DataSomeValuesFrom was recently added. The problem here is that only a particular set of datatypes is supported (which is necessary to obtain the desired computational properties):

• rdf:PlainLiteral
• rdf:XMLLiteral
• rdfs:Literal
• owl:real
• owl:rational
• xsd:decimal
• xsd:integer
• xsd:nonNegativeInteger
• xsd:string
• xsd:normalizedString
• xsd:token
• xsd:Name
• xsd:NCName
• xsd:NMTOKEN
• xsd:hexBinary
• xsd:base64Binary
• xsd:anyURI
• xsd:dateTime
• xsd:dateTimeStamp

This means, that e.g. xsd:double can not be used and it's not clear how to handle such cases.