datapath = the path to resolve the resource paths (RDF(S), properties, icon, etc),
same syntax as CLASSPATH; the path is relative to the directory where Corese has
been launched
This exception is used for semantic errors: (one exception is raised for
all the semantic errors that may occur)
Undefined prefix
Undefined property: in case of a triple of kind "A c:prop B", we check if the property "c:prop" exists
Undefined class: in case of a triple of kind "A rdf:type B", we check if B is a defined class