This class is used to support the parsing of single frames in Manchester OWL
syntax. The main purpose is to always return a requested OWL entity without
actually checking whether it was defined beforehand. This is required since
the Mancherster OWL syntax parser has to deal with single frames without
having access to a whole ontology.
Another purpose of this entity checker is to expand namespace abbreviations.
String containing the default namespace which will be
used to expand non-full URIs