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Considerations about Dublin Core
The → Dublin Core metadata standard is a simple yet effective element set for describing a wide range of networked resources.
The Dublin Core standard includes two levels: Simple and Qualified. Simple Dublin Core comprises fifteen elements; Qualified Dublin Core includes an additional element, Audience, as well as a group of element refinements (also called qualifiers) that refine the semantics of the elements in ways that may be useful in resource discovery.
The semantics of Dublin Core have been established by an international, cross-disciplinary group of professionals from librarianship, computer science, text encoding, the museum community, and other related fields of scholarship and practice.
Another way to look at Dublin Core is as a "small language for making a particular class of statements about resources". In this language, there are two classes of terms - elements (nouns) and qualifiers (adjectives) – which can be arranged into a simple pattern of statements.
The resources themselves are the implied subjects in this language. In the diverse world of the Internet, Dublin Core can be seen as a "metadata pidgin for digital tourists": easily grasped, but not necessarily up to the task of expressing complex relationships or concepts.
Each element of Dublin Core is optional and may be repeated. Most elements also have a limited set of qualifiers or refinements, attributes that may be used to further refine (not extend) the meaning of the element. The Dublin Core Metadata Initiative (DCMI) has established standard ways to refine elements and encourage the use of encoding and vocabulary schemes.
Three other Dublin Core principles bear mentioning here, as they are critical to understanding how to think about the relationship of metadata to the underlying resources they describe.
In general Dublin Core metadata describes one manifestation or version of a resource, rather than assuming that manifestations stand in for one another. For instance, a JPEG image of the Mona Lisa has much in common with the original painting, but it is not the same as the painting. As such, the digital image should be described as itself, most likely with the creator of the digital image as Creator or Contributor, rather than the painter of the original Mona Lisa.
The relationship between the metadata for both the original and the reproduction is part of the metadata description, and assists the user in determining whether he or she needs to go to the Louvre for the original, or whether his/her need can be met by a reproduction.
The qualification of Dublin Core properties is guided by a rule known colloquially as the Dumb-Down Principle. According to this rule, a client should be able to ignore any qualifier and use the value as if it were unqualified. While this may result in some loss of specificity, the remaining element value (minus the qualifier) must continue to be generally correct and useful for discovery. Qualification is therefore supposed only to refine, not extend the semantic scope of a property.
Best practice for a particular element or qualifier may vary by context, but in general an implementer cannot always predict that the interpreter of the metadata will always be a machine. This may impose certain constraints on how metadata is constructed, but the requirement of usefulness for discovery should be kept in mind.
Although the Dublin Core was originally developed with an eye to describing document-like objects (because traditional text resources are fairly well understood), DC metadata can be applied to other resources as well. Its suitability for use with particular non-document resources will depend to some extent on how closely their metadata resembles typical document metadata and also what purpose the metadata is intended to serve.
[Mikolaj Lesczuk]
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