Describing the relationship between surrogates is also difficult. Both the image and the photo have metadata associated with them. A patron searching specifically for the original photo may have difficulty distinguishing between references to the photo itself and references to the image. In order to address some of the weaknesses in the Dublin Core, a series of qualifiers have been proposed to refine the core element set. Schemes describe the syntax used by element values.
Types refine the core element itself.
The Dublin Core Workshops have set two limitations on qualifiers. First, a qualifier can only refine an element, not re-define its semantics. Second, the content must still be understood if the element is used without qualifiers. While qualifiers enhance the quality of description in the Dublin Core, they add complexity to the schema without necessarily addressing the needs of specialized communities. Many of these communities have developed their own metadata sets like MESL, the VRA Core, and others.