Just to give some example of what the situation is, consider the profile of Dublin Core which is specified at page 32 in the following document
http://www.adobe.com/content/dam/Adobe/en/devnet/xmp/pdfs/XMPSpecificationPart1.pdf which quotes "The XMP data modelling of these is consistent with apparent Dublin Core intent, but specific to XMP. As a corollary of the data modelling, the RDF serialization of Dublin Core in XMP might not exactly match other RDF usage of Dublin Core element set. XMP does not “include Dublin Core” in any fuller sense." I'd agree with them that the DC vocabulary was incomplete and failed to address a number of critical issues with DC at that time, such as what to do when a work has multiple authors (people care about that.) I can pick many nits, but the XMP profile would do what most people would want to do. It does not compete with MARC for bibliographic supremacy, but would it be good for the average dogpile of documents, yes it would. Other people have their own answers to what is unclear in DC, so it's fair to say that a triple store full of "Dublin Core" vocabulary could have a lot of stuff in it. For instance, some people might use strings and others might use VIAF identifiers or links to DBpedia or whatever. If you're aggregating at you will run into this and you really need a systematic way of solving the puzzle one bit at a time.
