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NOTE: This text, last edited in 2003, reflects the state of metadata art in the early 2000s. A completely revised FAQ is being developed at the wiki page http://wiki.dublincore.org/index.php/FAQ. Some of the questions asked in this 2003 FAQ are being incorporated into a revised Glossary at http://wiki.dublincore.org/index.php/Glossary.
What is metadata?
The simplest definition of metadata is " structured data about data."
Metadata is descriptive information about an object or resource whether it be physical or electronic. While metadata itself is relatively new, the underlying concepts behind metadata have been in use for as long as collections of information have been organized. Library card catalogs represent a well-established type of metadata that has served as collection management and resource discovery tools for decades.
Metadata can be generated either "by hand" or derived automatically using software.
Where is the metadata on the Dublin Core website?
We use separate .rdf files that contain the Dublin Core metadata information rather than including the metadata in the HTML. If you look at most of the pages on the DCMI Website, you'll see a link to the metadata at the bottom of each web page.
What is a resource?
In Web terminology, a resource is "anything addressable via a URL." However, Dublin Core implementations are not necessarily Web-based.
Dublin Core metadata can be used to describe any kind of resource - including various collections of documents and non-electronic forms of media such as a museum or library archive.
What is resource discovery?
A card catalog is the most common physical representation of a metadata system and is a perfect example of a system originally devised for locating resources that evolved into its own information system.
What is the Dublin Core Metadata Initiative?
The Dublin Core Metadata Initiative (DCMI) is an organization dedicated to fostering the widespread adoption of interoperable metadata standards and promoting the development of specialized metadata vocabularies for describing resources to enable more intelligent resource discovery systems.
The first Dublin Core Series Workshop took place in Dublin, Ohio in 1995. Since that time, the DCMI has been committed to the continual refinement of a "core" foundation of property types and values to provide vertically specific (semantic)information about Web resources, much in the same way a library card catalog provide indexes of book properties.
What is the Dublin Core?
Dublin Core metadata is used to supplement existing methods for searching and indexing Web-based metadata, regardless of whether the corresponding resource is an electronic document or a "real" physical object.
The Dublin Core Metadata Element Set (DCMES) was the first metadata standard deliverable out of the DCMI was an IETF RFC 2413. DCMES provides a semantic vocabulary for describing the "core" information properties, such as "Description" and "Creator" and "Date".
Dublin Core metadata provides card catalog-like definitions for defining the properties of objects for Web-based resource discovery systems.
What is the Dublin Core Metadata Element Set?
The Dublin Core Metadata Element Set is a set of 15 descriptive semantic definitions. It represents a core set of elements likely to be useful across a broad range of vertical industries and disciplines of study.
The Dublin Core Metadata Element Set was created to provide a core set of elements that could be shared across disciplines or within any type of organization needing to organize and classify information.
Who can benefit from using Dublin Core metadata?
Anyone can use Dublin core metadata to describe the resources of an information system. Web pages are one of the most common types of resources to utilize the Dublin Core's descriptions, usually within HTML's meta tags however increasingly there are many digital archives of physical objects that are starting to make use of the Dublin Core.
Dublin Core metadata is being used as the basis for descriptive systems by several community interest groups such as:
- educational organizations
- government institutions
- scientific research sector
- Web page authors
- businesses requiring more searchable sites
- corporations with vast knowledge management systems
(See also our listing of Dublin Core-based projects).
What is the difference between "Simple" ("unqualified") and "Qualified" Dublin Core?
"Simple Dublin Core" is Dublin Core metadata that uses no qualifiers; only the main 15 elements of the Dublin Core Metadata Element Set are expressed as simple attribute-value pairs without any "qualifiers" (such as encoding schemes, enumerated lists of values, or other processing clues) to provide more detailed information about a resource.
"Qualified Dublin Core" employs additional qualifiers to further refine the meaning of a resource. One use for such qualifiers are to indicate if a metadata value is a compound or structured value, rather than just a string.
Qualifiers allow applications to increase the specificity or precision of the metadata. They may also introduce complexity that could impair the metadata's compatibility with other Dublin Core software applications. With this in mind, designers should only select from the set of approved Dublin Core qualifiers that were developed by the Dublin Core community process.
Unfortunately, qualifiers often introduce additional complexity that can make metadata less interoperable unless approved DC Qualifiers developed within the DCMI are used with such interoperability considerations in mind.
A "date" is one example of a DC element that has the option of being further specified to identify it as a particular kind of date (date last modified, date published, etc.).
The use of a controlled vocabulary, such as Dewey Decimal Classification, is another method that could be used to further "qualify" the meaning of resource.
For examples of embedding qualified DC in HTML please read the "Qualified HTML Examples" section of the "Using Dublin Core" usage guide.
The Australian Government Locator Service is a good example of a major implementation using Dublin Core metadata that has added four local elements to Dublin Core in the proper, recommended way.
How do I begin implementing the Dublin Core Metadata Element set and where can I ask questions if I have questions regarding my implementation?
This is one of the most often asked questions and perhaps the most difficult to provide a catch-all answer. The wise ones say, "It depends." Unfortunately, that is the truth. It depends on your hardware, software, system resources and the goals you are trying to achieve. In a nutshell, we have a Usage Guide which provides some insight. Beyond that, we highly recommend posing questions to the DC-General mailing list. Most questions can be answered there or redirected to a place where the answer can be found.
What is the relationship between the DCMI and other Internet Standards groups?
The Dublin Core Metadata Initiative (DCMI) is a consensus building organization that has relationships with many standards activities. A number of people in the DCMI are active in the World Wide Web Consortium (W3C) (DC is the prototype application that drove the development of the Resource Description Framework, or RDF in the W3C).
Our own standardization activities take place in the IETF (RFC 2413 is reference description of the initial version of the Dublin Core), and there are currently formal DC standardization activities underway in CEN (the European Information Industry Standardization Forum) and in NISO (the North American Information Standardization Organization) and the IEEE (Institute of Electrical and Electronics Engineers).
Was Dublin Core metadata designed to be used only to describe digital and Web-based resources?
No. The scope of the Dublin Core was specifically designed to provide a metadata vocabulary of "core" properties able to provide basic descriptive information about any kind of resource, regardless of the media format, area of specialization or cultural origin. It is important that a semantic model used for resource discovery is not dependent on the medium of the resource it means to describe.
The Dublin Core metadata vocabulary is the result of many years of collaborative research to determine a common set of properties universal for describing any type of resource. The use of a standardized general classifications system also enables metadata of such collections to be combined and for knowledge contained within each collection to be shared.
Since most Dublin Core implementations only need to process a resource's descriptive metadata, the medium of that resource becomes a non-issue. This enables DC metadata to be used by museums and other organizations interested in cataloging specialized types of mixed-media collections, while maintaining an open framework preserving their ability to share metadata with other DC implementors.
How is Dublin Core metadata used?
The term "Dublin Core metadata" is usually in reference to the 15 elements of the Dublin Core Metadata Element Set (DCMES) and its limited set of optional approved qualifiers tested and approved as "safe" for use by the Dublin Core community.
The DCMES was published in 1998 as an IETF RFC 2413. Dublin Core metadata is used to supplement existing methods for searching and indexing Web-based resources, providing a semantic vocabulary to describing the "core" properties of a resource object (such as "Description" and "Creator" and "Date").
How is Dublin Core metadata stored?
Dublin Core metadata is often stored as name-value pairs within META tags, which are placed within the HEAD elements of an HTML document.
However, it can also be located in an external document or loaded into a database enabling it to be indexed and manipulated from within a propriety application.
How can I embed Dublin Core metadata within my HTML documents?
Dublin Core metadata can be stored using the meta element in the head of HTML documents. An informational IETF RFC (2731) titled "Encoding Dublin Core Metadata in HTML" defines the standard way to do this. A DCMI Note describes one method for storing Qualified DC in HTML.
What is the relationship between Dublin Core Metadata and RDF and XML?
Dublin Core Metadata Element Set (IETF RFC 2413) and RDF (Resource Description Framework) (W3C Recommendation) are two distinct specifications. Neither requires the other, but their co-evolution forms a natural complement within the Web's greater metadata architecture.
Both the Dublin Core and RDF communities have a number of members in common, and have evolved side-by-side. The Dublin Core community provided much of the basic requirements that were used to design RDF. In turn, the development of RDF provided the Dublin Core community with a much more formal underlying data model that has helped it to determine best practices and universal solutions (rather than ad hoc Band-Aids) for many of the detailed problems that were encountered during the deployment process.
Below is an example of how the Dublin Core vocabulary can be used to define additional semantics about the resources described within an RDF fragment:<?xml version="1.0" ?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/dc/elements/1.1/"> <rdf:Description about="http://purl.org/DC/documents/notes-cox-816.htm"> <dc:title>Recording qualified Dublin Core metadata in HTML</dc:title> <dc:description> We describe a notation for recording qualified Dublin Core metadata in HTML meta elements. The syntax includes recommended usage of the standard HTML syntax to record the different classes of qualification needed to represent the model.</dc:description> <dc:date>1999-08-18</dc:date> <dc:format>text/html</dc:format> <dc:language>en</dc:language> <dc:publisher>Dublin Core Metadata Initiative</dc:publisher> </rdf:Description> </rdf:RDF>
What is the Dublin Core data model?
The basic Dublin Core data model is defined by its 15 elements and the relationships defined between the resource-of-interest and whatever other resource is "in-scope" for DC.
In particular, the "Relation" and "source" elements are used to indicate a connection with another resource of any type. "Creator", "Contributor" and "Publisher" elements relate the present resource to a party who has some responsibility for it. The "Coverage" element relates the present resource to a place or to a time-period. The value recorded for each of these elements, therefore, should normally be strictly an identifier of another resource, which could have its own DCMES description.
A completely abstracted DC data model must also include its two types of qualifiers. Value qualifiers (which store an identifier for the vocabulary, encoding or language of the value) and element qualifiers, which are used to further refine the semantic meaning of an element.
However, many users have found it useful to add extra information to Dublin Core descriptions. Particularly when values are frequently drawn from a controlled vocabulary (e.g. a keyword list, such as Library of Congress Subject Headings, LCSH), or written using a special notation (e.g. the ISO8601 format for dates and times).
Other techniques include using a particular natural language (in the case of values written in text-strings), which would make the information more useful if a client were informed of the source for this vocabulary, the definition of the notation, or the name of the language used.
How do I participate in a discussion about the Dublin Core?
Anyone may participate in discussions about Dublin Core metadata by simply joining the appropriate mailing list for the working group activity of interest.
The DC-General mailing list is the general forum for community participation and submitting general feedback.
What is the maximum length for each field in Dublin Core?
There are no limits to field length.
What search-engines support the Dublin Core Metadata Element Set?
Several commercial and non-commercial search engines will index META elements with just a little configuration.
A recent inquiry on the dc-general mailing list produced this list:
- Microsoft's Index Server
- Blue Angel Technologies MetaStar
- Verity Search 97 Information Server
To get a good overview of what software is out there see Search Tools and Search Engine Watch.
The well-known "all the Web" search engines including AltaVista, Yahoo, HotBot, etc. tend to avoid using the information found in meta elements in their indexing. This is because, unless the pages are from guaranteed "trusted" servers, the meta information is commonly used by unscrupulous content-providers for spamming, to mislead the indexes into givingWeb-pages a misleading rating.
What is an attribute-value pair?
Attribute-value pairs are used within Dublin Core metadata to represent the properties of a resource or object.
Information such as "Author", "Creator" and "Date" are all examples of Dublin Core elements that are implemented as attribute-value pairs within HTML's META element to provide additional semantics about a resource.
Web resources are effectively information objects complete with properties that can be expressed in any number of ways. The Dublin Core Metadata Element Set (DCMES) enables properties to be assigned to a Web resource the exact same way we might fill in the blanks for a card catalog record.
What is the Warwick Framework?
The Warwick Framework is a set of design principles that have guided the development of the Dublin Core since the Second Dublin Core Metadata Workshop in Warwick, UK.
The Warwick provides a metadata-based school of thought that believes different kinds of metadata can be used to describe the same resource in disparate ways to accomplish different goals.
For more information about the Warwick Framework, please read "The Warwick Metadata Workshop: A Framework for the Deployment of Resource Description".
Can I add a new element to Dublin Core?
In theory, yes. A DCMES element specified with an element qualifier is, effectively, a "new" element or property- with a more specialized meaning than its parent element.
However, it is not possible to create a new Dublin Core element whose meaning goes beyond the scope of of the original elements in the DCMES.
It is expected that local or application-specific requirements may require additional qualifiers or elements that have not been approved by the Dublin Core community at large. Nevertheless, designers should employ additional qualifiers with both caution and the understanding that interoperability could suffer as a result.
In cases where additional qualifiers are being utilized, it may be helpful to bring this to alert the Dublin Core Directorate in order to promote the wider use of such qualifiers.
For examples of embedding qualified DC in HTML please read the "Qualified HTML Examples" section of the "Using Dublin Core" usage guide.
What is the Open Metadata Registry?
The DCMI's Open Metadata Registry is a Web-based semantic modeling tool that uses a form-driven user interface to enable an end-user to define relationships between different vocabularies.
The semantic framework for the application was created using Dublin Core metadata and RDF Schemas.
How do I store proper names in Dublin Core metadata?
The encoding of personal names is a difficult task within most metadata systems, and DC is no exception. The difficult part is that naming conventions tend to vary from culture to culture.
The recommendation for Dublin Core metadata is to encode the family name first, which supports effective collation of names and is consistent with most naming conventions globally.
What is the "Dumb-Down" Principle?
The so called "Dumb-Down Principle" simply means that in any use of a qualified DC element, the qualifier may be dropped and the remaining value of the element should still be a term that is useful for discovery.
For example, there are several date qualifiers that might be used to enhance the precision of various dates associated with a resource. Dropping the date qualifier (say, for example, Date-Created) will still leave a useful date for discovery, though perhaps not quite as useful as if the qualifier were included.
Similarly, the specification of a subject term from LCSH, for example, is still useful even if one does not know it was selected from a controlled vocabulary.
The basic idea is that qualifiers should improve the precision of a piece of metadata, but the metadata should still be useful even without that extra precision (that is, dropping the qualifier has 'dumbed-down' the metadata).
How can I use existing controlled vocabularies for DC Subject metadata?
One can assign a metadata value selected from a controlled vocabulary as the value of the element, and then qualify that element with the name or identifier of the scheme from which it is selected (the specifics of the encoding depends on the syntax being employed. Refer to DCMI specifications for details of encoding DC metadta in HTML, XML, or RDF/XML.
DCMI registers controlled vocabularies and encoding schemes to promote their use and to facilitate consistent identification within DC metadata. Application designers should review registered controlled vocabularies to determine if there is a suitable one for their application, and use the registered name of that vocabulary in their application. For example, "DDC" is the registered Name for the Dewey Decimal Classification, and should be used as the value of the qualifier. By using registered Names or tokens to designate schemes, metadata from different applications that use common controlled vocabularies are more likely to be interoperable.
The mechanics of selecting a value from such a vocabulary is dependent on the application. It is expected that metadata editors for some domains will have tools to support such selection, but it can also be done with conventional print-based references.
Can I use controlled vocabularies that are not approved by DCMI?
Yes. DCMI registers only those controlled vocabularies that have been brought to our attention. There are, of course, many others that are equally legitimate, and it has always been our intent that communities of expertise be able to leverage the value of such existing schemes in their metadata. To promote interoperability, it is recommended that application designers review registered controlled vocabularies for one that may be suitable for their application. If a controlled vocabulary of choice is not registered with DCMI, it is possible (but not mandatory) to register it. Registration assures that others who adopt this vocabulary use the same Name token in their metadta, thereby promoting interoperability.
It is important to note that DCMI 'registers' controlled vocabularies, rather than 'approving' them. Controlled vocabularies are generally the result of substantial community expertise. It is not in the purview of DCMI to approve or disapprove such works, but rather help to make them visible for others who might choose to adopt them, and to prevent Name collisions by assigning unique tokens to identify them within DC metadata.
What are the names of the DCMI namespaces?
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