A bit about Unit 4 from my current MOOC undertaking, Metadata: Discovering and Organizing Information.
If there are so many metadata schemas out there, which one should you choose? Well, that depends. It depends on lots of things: The type of collection being described, the needs and goals of the end users, the particular requirements for a collection, and so forth. Do you only need, for example, to describe something in broad, general terms, or do you need to go into greater detail, “drill down,” that is, into the depths of an artistic object, exploring its various facets?
The metadata schema Dublin Core is very widely used. However, if you need to provide rich, descriptive detail for a community of art historians, you might want to consider using the Catalog for the Description for Works of Art, or the CDWA. The CDWA, which comes out of the J. Paul Getty Institute, is a schema which is meant for the description of objects of art.
The use of metadata schemas goes hand in hand with the use of controlled vocabularies and thesauri in order to increase the likelihood that the objects being described will be discovered by those who wish to find them. In the world of library science and metadata, thesauri and controlled vocabularies are almost synonymous. Controlled vocabularies are defined lists of words and phrases. Thesauri describe relationships of words beyond synonyms and antonyms. Thesauri intended for the use of the creation of metadata include, for example, relationships of words that define terms that are broader and/or narrower in relation to various words, as well as terms that are used in place of terms that might also be used to describe an object.
The Thesaurus of Art and Architecture, also created by the Getty Institute, is a thesaurus which can be used along with any metadata schema for providing values for various elements that are chosen to describe an object. The AAT works very well with the CDWA and is often recommended throughout the schema as the preferred choice of authority source. Another thesaurus is the Thesaurus for Graphic Materials, the TGM, a product of the Library of Congress, and especially useful for the description of graphic materials, such as photographs. Need a particular vocabulary to describe geographic territories? You might want to try the Thesaurus for Geographic Names, the TGN, also put out by the Library of Congress.