Many different opinions exist on how to classify the different types of metadata. In the interest of simplicity, metadata is most commonly described as consisting of three types: administrative, structural, and descriptive. (LOC, NISO, Taylor) As new metadata issues are recognized and usage evolves, these three categories are often further divided with subcategories or described with additional categories (Baca, Taylor). Administrative metadata, used in managing and administrating information resources, consists of three sub categories: preservation metadata, access and rights metadata, and even meta-metadata. Structural metadata may be referred to as technical, display, or use metadata. Additionally, structural metadata is often divided into presentation and navigation categories. This is a useful distinction to make as the separation of presentation and structure is a common development goal for information systems. Descriptive metadata used to describe or identify information resources remains consistent in most attempts at categorizing metadata types.
Despite the confusion surrounding the various metadata categories, it is important to design a metadata strategy that will accommodate the various uses within a given system and domain. In the capacity of designing metadata, the more detailed category lists are more useful as they provide for more complete and sophisticated usage of metadata.
Dublin Core is a metadata standard designed to be easily used across domains. It was intentionally designed to be simple in its design and implementation with the idea of acting as the lowest common denominator of metadata standards, the theory being that some metadata is better than none at all. Some flexibility within the standard was included by allowing for the core set to be extended as needed for particular domains, making all elements optional and repeatable, and allowing all elements to be modified by a qualifier. Dublin Core may be encoded either in HTML or RDF/XML.
METS (Metadata Encoding & Transmission Standard) is more of a framework for encoding metadata than a metadata standard. It was designed specifically for managing digital objects with the recognition that descriptive and structural metadata are critical to using and evaluating digital objects. As a result, METS is stricter than Dublin Core in its requirements and more difficult to implement. However, like Dublin Core, METS was also designed to be flexible and extensible. METS does not define the elements in the administrative and descriptive sections, but rather allows a choice of extension schemas. As an example, one could choose to use Dublin Core as the descriptive metadata schema within a METS package. Also like Dublin Core, METS is encoded in XML.
MPEG-21, like METS, is a framework designed to enable use of digital resources across networks and devices. In the case of MPEG-21, it was designed to support multimedia applications and accommodate interoperable and automated transactions with specific attention to Intellectual Property Management and Protection requirements. Also like METS, MPEG-21 focuses on the definition of a fundamental unit of distribution and transaction, but unlike Dublin Core and METS, its framework covers the entire information chain, rather than just the digital object. Like both Dublin Core and METS, MPEG-21 is encoded with XML.
Baca, M. ed.(2000). Introduction to Metadata, Pathway to Digital Information. Getty Information Institute. Retrieved 07/06/2005
Dublin Core Metadata Initiative (DCIM). Retrieved 07/06/2005 from http://dublincore.org
Library of Congress digital repository development - core metadata elements. Retrieved 07/06/2005 from http://www.loc.gov/standards/metadata.html
Metadata Encoding & Transmission Standard (METS). Retrieved 07/06/2005 from http://www.loc.gov/standards/mets
Moving Picture Experts Group (MPEG-21). Retrieved 07/06/2005 from http://www.chiariglione.org/mpeg/standards/mpeg-21/mpeg-21.htm
NISO (2004). Understanding Metadata. Bethesda, MD: NISO Press. Retrieved 07/06/2005 from http://www.niso.org/standards/resources/UnderstandingMetadata.pdf
Taylor, A. (2004). The organization of information. Westport, CT: Libraries Unlimited.