Metadata Focus and Depth
A taxonomy provides a way to describe content. It is a source of conceptual descriptions for filling the subject metadata field in database records. When you look at a metadata schema, regardless of who built it, there is some field or element specified for the description of the concept represented in the item. It might be called the subject, descriptor, keyword, or something else. Dublin Core is one of the well-known metadata schemas. (To my mind it is not fully a standard; even though you will find my name on the standard for Z39.84, I still think it is just a guideline.)