IdentifyingTheResource
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Note: Summary of best practices added. Jenn Riley 10/11/05
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[edit] Identifiers
[edit] Summary of Best Practices
- Include recognized standard identifiers when available.
- Include a URI or DOI linking to the resource when available.
- Explicitly encode the nature of an identifier provided.
- Express multiple identifiers in repeated fields.
See also Linking from a Record to a Resource and Other Linking Issues
Identifiers are a way to unambiguously identify a resource. For analog materials, identifiers might be a standard record number such as an ISBN or ISSN or a classification number. Digital materials may also have an ISBN or ISSN, but may also have some sort of standard digital identifier such as a URI (Uniform Resource Identifier) or a DOI (Digital Object Identifier). This section discusses both analog and digital identifiers.
[edit] Identifying the Resource
As discussed in the Linking from a Record to a Resource section, identifiers can be critical to the discovery of the resources (digital or analog) described by metadata. A ISBN provides an unambiguous identifier for a specific edition of a monograph and aids the end-user in finding that specific edition. A DOI will does the same thing for an article in an online journal, for example.
When a recognized standard identifier (ISBN, ISSN, DOI, etc.) exists for an item (or for the work of which it is a manifestation), best practice calls for including such an identifier in the metadata. This holds for both digital and analog resources. In cases where no globally recognized standard identifier exists, a local identifier should be included in the metadata.
Ideally the URI or DOI for a digital resource will resolve (i.e. be a URL) to the resource. If the digital identifier does not locate the digital resource, it is important to provide, in addition to the identifier, a URL (Uniform Resource Locator) which will direct a user to the resource. In aggregations of metadata describing digital resources, the link between the metadata and the actual resource is crucial; without it the user will not be able to reach the resource without time consuming work arounds. This is a matter of credibility for both service providers and data providers.
In many cases, a URL will be the only 'identifier' included in a metadata record. It is important to note that a URL may not actually be the 'unambiguous identifier' for the resource as URLs often change, and as the URL included in the metadata record may not actually resolve to the resource itself, but to a page with a link to the resource, to a page with the resource and metadata, or to a collection homepage. For more information about linking to the resource, see the Linking from the Record to the Resource section.
[edit] Formatting Identifiers
If using a standard identifier, it is best practice to format the identifier according to that standard. This is especially true for identifiers that are meant to be machine processable such as URIs (see http://www.ietf.org/rfc/rfc2396.txt and http://www.ietf.org/rfc/rfc2732.txt) and DOIs (http://www.doi.org/handbook_2000/enumeration.html#2.2).
When using a metadata format that allows explicit coding of the type of identifier, best practice is to code this information including for local identifiers.
Example of coding a standard identifier in Qualified Dublin Core:
<dc:identifier xsi:type="dcterms:URI"> http://mathworld.wolfram.com/ </dc:identifier>
Example of coding a local identifier in MODS:
<mods:identifier displayLabel="IU Archives number" type="local"> P07959 </mods:identifier>
In general, when using identifiers that are not actionable and cannot be adequately referenced within the metadata itself, it is useful to provide a prefix. For instance, ISSNs and ISBNs can be prefixed, allowing them to be more easily understood by humans and machines.
Example in simple DC:
<dc:title>International comparison of social housing management in western Europe</dc:title>
<dc:creator>Boelhouwer, P.J.</dc:creator>
<dc:type>Article / letter to the editor</dc:type>
<dc:identifier>ISSN 1383-2336</dc:identifier>
See DC TUDelft Article 1 for the complete record from which this example was taken.
[edit] Multiple Identifiers
Multiple identifiers should be included if they will assist a service provider or an end-user in locating the resource described.
However, in the case of digital objects, if the identifiers resolve to multiple versions of the resource, it is important to identify a single primary identifier that a service provider can label or use as the primary link to the resource. For example, only one <dc:identifier> element should be included with an actionable identifier (i.e. a URL). Additional <dc:identifier> elements might be included with a local identifier if not actionable (i.e. an end-user cannot click on the identifier to arrive at the resource). Again see Linking from the Record to the Resource for a discussion of best practices related to use of URLs.
