semantic web - protege how to add a reference to another ontologya -

i tying integrate ontology ontologies. did importing ontologies in protege, works, protege lists classes, normally. looking if there way in reference (uri) of these ontologies , can use them prefix.

ofc, building ontology using owl2

i hope me

if want reason , materialise facts based on terms relating referenced concept, need import ontology referenced concept belongs.

e.g given external ontology following statements:

ex:person owl:class;    rdfs:subclassof ex:agent. 

if reference in without importing:

ex2:doctor owl:class;    rdfs:subclassof ex:person. 

and make following statement:

ex2:jack ex2:doctor. 

an run through reasoner, materialise following:

ex2:jack ex:person. 

but not following:

ex2:jack ex:agent. 

to materialise latter, need import ontology statements ex:person.