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Using Metadata Standards
By Sarah Higgins, Aberystwyth University
Published: February 2007
Metadata is the backbone of digital curation. Without it a digital resource may be irretrievable, unidentifiable or unusable. Metadata is descriptive or contextual information which refers to, or is associated with, another object or resource.
This usually takes the form of a structured set of elements which describe the information resource and assists in the identification, location and retrieval of it by users, while facilitating content and access management.
Metadata standards formalise the element structure to ensure that the aims of a user community can be fulfilled. More information concerning the nature of a metadata standard can be found in DCC Standards Watch 1: What are Metadata Standards?
Using metadata standards, from the outset of a project, ensures rich, consistent metadata which will support the long-term discovery, use and integrity of digital resources. The result is effective searching, improved digital curation and the possibility of sharing. Metadata standards enable interoperability — metadata from a variety of sources can be integrated into other technical systems or machine read by compatible ones. Increasingly federated searching across a number of metadata standards and repositories is implemented. If metadata standards have been adopted the potential for resource discovery is much greater.
Types of Metadata Standards
Effective implementation of metadata standards needs early consideration of the structure, content, functionality and links between digital objects and metadata instances required. Different types of metadata standards are used interdependently to achieve the following aims:
- Metadata structure standards ensure consistent structure across individual entries; enable data searching to be implemented and data sharing across a discipline. Hierarchical structure standards enable context as well as content to be described.
- Metadata content rules enable consistent data entry for effective searching. Content rules include: vocabularies and semantic rules as well as authority files, thesauri, classifications and ontologies.
- Metadata mark-up standards ensure that metadata is machine readable and that automated searches can be undertaken.
- Metadata packaging standards define the links between digital objects and their metadata while binding the components into archival packages as defined by the OAIS Reference Model (Open Archival Information Systems Reference Model — ISO 14721:2003)
When choosing which metadata standards to implement the following need to be considered:
- The context in which the metadata will be created and used — best practice is to use a standard which has been developed with a particular community in mind. Consider who data may be shared with and who will be using the result. Communities often have de facto standards which have been tried and tested e.g.: ISAD(G)2 (International Standard Archival Description (General), 2nd Edition) is a structure standard for describing archival materials, AACR2 (Anglo-American Cataloguing Rules, 2nd Edition) is a content standard for cataloguing book materials.
- The format of the material being described — if the resource is in one particular format e.g. digital still images or audio files, there may be metadata standards which are particularly applicable. An example is the structure standard VRA Core Categories, currently Version 3.0, for works of culture and accompanying digital image.
- The budget — metadata creation is expensive but it is worth creating the best possible data that the budget will allow. It is easy to present a simpler form of the full metadata if purpose determines, but it is difficult to enhance it at a later date. Providing access points can account for a large percentage of the budget but the functionality and searchability will be significantly enhanced.
- The metadata capture method — much technical metadata can be readily auto-generated and is cheaper to collect but descriptive metadata generally requires a degree of manual input. The creation of links between the metadata and the digital resources it describes needs careful management. Effective work-flow design, quality assurance methodology and staff training will ensure that standards remain high and errors are reduced.
- Metadata storage and delivery — the storage and delivery of both the metadata and the digital resource it describes need to be considered. Choices of software tools will have a bearing on choices concerning which metadata standards to implement and whether to embed or reference digital objects. The expected end-use will influence which metadata elements to use, e.g. to provide a structured search for a personal name, you must index those names.
Metadata standards often take account of every eventuality and may have a large number of elements to accommodate these. It is not necessary to use every element provided. A core of elements are usually designated as mandatory or mandatory if applicable. The rest are generally optional.
Once you have chosen relevant metadata standards the functionality required can be analysed by creating use cases. The metadata elements which will fulfil both your aims and the standard's requirements for conformity can be identified, along with any desirable extensions. An application profile which will fulfil your aims can then be developed. Some standards maintenance bodies hold registers of application profiles so that those with similar requirements can share their specifications.
An example is the Library of Congress maintained standard METS (Metadata Encoding and Transmission Standard) which registers peer reviewed profiles and makes them available to the wider user community on the website. The Dublin Core Metadata Initiative works with different disciplines to develop and ratify community specific application profiles which extend and qualify the original 15 core elements with new elements and element refinements or qualifiers.
When creating a profile it is desirable to ensure that you use the elements in your chosen standard which correspond to the 15 elements of the Dublin Core metadata element set (ISO 15836:2003E). These are generally regarded as the minimum information required for adequate resource description. In addition, these are the elements which are most likely to be used for creating indexes and searches.
If your resource is to be harvested using the Open Archives Initiative — Protocol for Metadata Harvesting (OAI-PMH) or be subject to federated searching across different metadata standards these elements will be required for the technical implementation. There are a number of published metadata crosswalks available. In some metadata standards, more than one element can be mapped to a Dublin Core element.
- Anglo-American Cataloguing Rules, Second Edition, 2002 Revision: 2005 Update, American Library Association, 2005
- Baca, Murtha (editor), Introduction to Metadata: Pathways to Digital Information, Online Edition, Version 2.1
- Dublin Core Metadata Initiative (DCMI)
- Haynes, David, Metadata for Information Management and Retrieval, Facet Publishing, 2004
- Information and documentation — The Dublin Core metadata element set (ISO 15836:2003E)
- ISAD(G) General International Standard Archival Description, 2nd Edition
- Metadata Mappings (Crosswalks)
- METS Profiles
- OAIS Reference Model (Open Archival Information Systems Reference Model — ISO 14721:2003)
- Open Archives Initiative — Protocol for Metadata Harvesting (OAI-PMH)
- VRA Core Categories, Version 3.0
- DCC Digital Curation Manual instalments on Metadata, Archival Metadata and Preservation Metadata
- DCC Standards Watch 1: What are Metadata Standards?
- DIFFUSE (Dissemination of InFormal and Formal Useful Specifications and Experiences) — collected information on standards relevant to the Information Society, originally maintained by TIEKE (the Finnish IT Development Centre), IC Focus and The SGML Centre but now repurposed and maintained by the DCC