protege how to use instances from ontology on the web - semantic-web

Question

In my ontology i have an instances named beethoven, how can I say that my beethoven instance is the same as this beethoven
http://dbpedia.org/page/Ludwig_van_Beethoven
I know that I have to use owl:sameAs predicate, but the thing is when I click on sameAs predicate, protege just give me a list of already existing instances. However, I'm asking about an instance from an ontology on the web.
What I was thinking of is maybe I have to import that ontology, but thing about it, if i want to sue dbpedia, do i really have to import the whole dbpedia to my machine?
Im sure there is something easier and that's why I'm asking you guys
Thanks in advance
Update 1
After reading this answer
Extend DBpedia entity in Protege ontology
I created an instance of the type THINKG in my protege and gave it the exact same URI (which is http://dbpedia.org/page/Ludwig_van_Beethoven ), and said that my beethoven instance is owl:sameAs this new instance, would that be enough?
Update2
I tried to query my ontology after the things that I have listed in update1, and I noticed this:
this query:
select ?z where
{
mo:Beethoven owl:sameAs ?z
}
returns empty result
However, this query:
select ?z where
{
dbpedia:Ludwig_van_Beethoven owl:sameAs ?z
}
returns my beethoven instance like this:
how can the dbpedia:beethoven is the same as mo:beethoven, but the other way around, knowing that I said mo:beethoven is owl:sameAs dbpedia:beethoven not the other way around

Answer 1

This is one of the important differences between RDF and OWL. RDF is just a bunch of triples. The triples:
:LVBeethoven owl:sameAs :LudwigVanBeethoven
and
:LudwigVanBeethoven owl:sameAs :LVBeethoven
are different triples. RDF graphs are just sets of triples.
OWL, on the other hand, is a logic, concerned with axioms and inferences. owl:sameAs is the equality predicate for OWL individuals, and equality predicates are symmetric (among other things). That means that from A owl:sameAs B an OWL reasoner can infer that B owl:sameAs A. So, if you have a reasoner attached to your SPARQL endpoint, you'll be able to query for either A owl:sameAs ?x or ?x owl:sameAs A and get B as a result. You can do some limited forms of OWL reasoning in SPARQL. In this case, you could use a property path to follow an owl:sameAs link in either direction:
select ?z where
{
mo:Beethoven (owl:sameAs|^owl:sameAs) ?z
}
For some more examples, see Using SPARQL for limited RDFS and OWL reasoning.