An international group of experts, united under the name Dublin Core Metadata Initiative, has developed a general system for Meta elements. Through which it is not only possible to express information about HTML documents, but also pictures, films, dates, and even physical objects. The system is easy to use and takes into consideration all the important information that can be conferred about an internet document. The Meta elements from Dublin Core have also been greeted warmly by the W3 consortium, who use them heavily with their RDF project.
Dublin Core primarily defines 15 attributes, or so-called elements, which can be assigned values. Additional sub-elements allow for special Meta elements. You will find a full list and description of the elements under the DCMI Meta data terms. The Dublin Core standard proposes some instructions for suitable schemata, including for media types, language abbreviations and information regarding the date.
The specification expressing Dublin Core in HTML/XHTML Meta and link elements describes how you should use certain Meta elements in your HTML file: The element name should be placed in the name attribute of the Meta tag, while the associated value should be placed in the content attribute. You can optionally enter the corresponding data format in the scheme attribute.
An Example:
<head profile=http://dublincore.org/documents/dcq-html/>
<link rel=“scheme.DC” href=http://purl.org/dc/elements/1.1>
<link rel=“scheme.DCTERMS” href=http://purl.org/dc/terms/>
<meta name=“DC.title” content=“SELFHTML: Meta elements”>
<meta name=“DC.creator” content=“Thomas Grady”>
<meta name=“DC.subject” content=“Meta elements”>
<meta name=“DC.description” content=“established Meta elements in HTML today”>
<meta name=“DC.publisher” content=“Thomas Grady”>
<meta name=“DC.contributer” content=“Ryan Howard”>
<meta name=“DC.date” content=“2008-5-8” scheme= “DCTERMS.W3CDTF”>
<meta name=“DC.type” content=“Text” scheme= “DCTERMS.DCMIType”>
<meta name=“DC.format” content=“text/html” scheme= “DCTERMS.IMT”>
<meta name=“DC.identifier”>
content=“http://www.html.co.uk/21/meta-elements-part-2.html”
scheme=“DCTERMS.URI”>
<meta name=“DC.source”
content=”http://www.w3.org/”
scheme=“DCTERMS.URI”>
<meta name=“DC.language” content=“en” scheme=“DCTERMS.RFC3066”>
<meta name=“DC.relation” content=http://dublincore.org/ scheme=“DCTERMS.URI”>
<meta name=“DC.coverage” content=“London” scheme=“DCTERMS.TGN”>
<meta name=“DC.rights” content=“All rights lie with the author”>
</head>
Explanation:
For programmes like search engines you can specifically define that your document is using the Dublin Core specification for embedding Meta elements in HTML.
With Meta elements, that belong to a certain public system, the name of the Meta element will be presented to the system as a short description. This prefix is DC for the 15 most commonly used elements with Dublin Core, and you must note DCTERMS for the sub-elements and schemata. The element name, or data format description, follows separated by a period. To clearly verify that all Meta elements with this prefix belong to the Dublin Core system, links are provided to the so-called naming space for Dublin Core. That way the uniqueness is ensured, even if other Meta data systems also operate with the same abbreviations.
With <meta name=“DC.title” content=“Title”> you can enter a title for the file, similar to the title element in HTML.
With <meta name=“DC.creator content=“Name”> you can reference the file’s original
creator.
With <meta name=“DC.subject” content=“Text”> you can specify the file’s topic.
With <meta name=“DC.description” content=“Text”> you can give a short description of the file’s content.
With <meta name=“DC.publisher” content=“Name”> you can enter who is responsible for the file’s publication. This can be the author themselves, or a publishing house, or a relative of a dead author.
With <meta name=“DC.contributor” content=“Name”> you can enter the co-authors or people who, next to the author, are responsible for the file’s content (such as translators, graphic designers, musicians etc).
With <meta name=“DC.date” content=“date”> you can enter when the file has been published. The date should adhere to a prevalent time and date format. You can specifically state, using the attribute= “DCTERMS.W3CDTF”, that the time entry adheres to such a system.
With <meta name=“DC.type” content=“Type”> you state the type of content you are making the Meta tags for. The following types are allowed:
Collection: If the content is a directory with links to sub-domains and the Meta elements are intended to describe the directory’s content.
Dataset: If the information is contained within a data set, such as a table.
Event: If the content is for an occurrence at some point in time, such as an exhibition or wedding.
Image: if the content is a visual representation, such as a photo, film, sketch or animation.
InteractiveResource: If the purpose of the site is based on interaction with the user, such as a registration form, embedded Java applet, or chat site.
PhysicalObject: If the site’s content concerns any physical object. Because this isn’t possible with HTML files, it makes little sense to specify it here. IF it is a visual representation of an object, choose image, choose text if it is a textual description, and sound if it is a sound description or effect.
Service: if the site performs a service, such as an online banking service.
Software: if the content offers software, for example, downloadable software and the Meta elements reference the software.
Sound: if the content is primarily acoustic, for example an embedded MP3 file or a streaming radio station.
Text: if the content is text oriented – regardless if it concerns literature, jokes, news scientific text or any other type of text.
Use the attribute scheme=“DCTERMS.DCMIType” in order to clearly specify that you are using these predefined types.
With <meta name=“DC.format” content=“Type”> you can state the file’s data format or media type. You can enter a MIME-Type for a value. The MIME-Type for HTML is text/html. You can make it clearer that the information concerns a media type in accordance with the official scheme using the scheme= “DCTERMS.IMT” attribute.
With <meta name=“DC.identifier” content=“value”> you can enter a unique number or address for the file. With websites, for example, this is the original URI. With the addition of scheme= “DCTERMS.URI” you make it clear the value is a valid URI.
With <meta name=“DC.source” content=”Source”> you can name the source from which the current file is drawn from or based on. In the example above we use a website as the source. However, you could name an offline publication or title. That would be the case if, for instance, the HTML file came from a book. If the source stems from an URI, then you can accentuate that with the scheme=“DCTERMS.URI” element.
With <meta name=“DC.language” content=“Language” you can enter the language in which the HTML file is written. A language abbreviation according to RFC 3066 is expected as a value for content.
With <meta name=“DC.relation” content=“Source”> you can enter what relation the current file has to any other projects it might belong to. The word in content should describe what type of relation.
With <meta name=“DC.coverage” content=“Text”> you can enter a geographical reference, or reference a point in time, for the file’s content. For geographical entries it can either be the location, longitude and latitude, a region, and the time reference can either be a date, or an age. We use a city name from the Ghetty Thesaurus of Geographical names as an example. The data format is noted as scheme=“DCTERMS.TGN”.
With <meta name=“DC.rights” content=“Text”> you can enter information regarding the file’s copyrights. You may also enter a URI where the exact legal conditions are specified. If you choose to reference a URI, then note the scheme=“DCTERMS.URI” attribute to ensure it is clear the value is a URI.
Take Note:
You do not have to use all of the Dublin Core Meta elements. It’s no problem if you only note the elements that make sense. Even noting the data formats with the scheme attribute is not completely necessary, but it is still recommended as long as the schemas exist.
Although the Dublin Core represents a well known and carefully worked through Meta data system, the practical uses of such Meta elements appear minute at first glance. The leading search engines completely ignore them, as a reaction to their previous misuse. So the use of Dublin Core Meta data is envisioned more where processing programmes can trust the Meta elements. Such Meta elements are well suited for the internal governing of large web sites, dynamically generating content directories, or internal website search functions, for example.
