The Dublin Core calls itself a "metadata initiative," and it provides an RDF content model that is in wide use to describe Web resources. The Dublin Core has attracted the attention of museums, libraries, government agencies, and commercial groups as a way of standardizing RDF for Web resources. You can find out all about the Dublin Core at its home page, www.purl.org/dc. In the previous example, I used a <Creator> property without specifying a namespace for that property. However, when you create your own properties, you should use a namespace to avoid conflicts. The Dublin Core's namespace is "http://purl.org/DC/" . In fact, the <Creator> property I've been using is modeled after the Dublin Core's <Creator> property. I can declare the Dublin Core's namespacewhich is usually given the prefix dc in the example document, and I can indicate that <Creator> is part of that namespace like this: <?xml version="1.0" ?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/DC/"> <rdf:Description about="http://www.starpowder.com/planets.html"> <dc:Creator>Nicolas Copernicus</dc:Creator> </rdf:Description> </rdf:RDF> The <Creator> property is just one Dublin Core property; you can find all the defined Dublin Core properties in Table 18-12. Table 18-12. Dublin Core Elements Element | Means this | Contributor | Person or organization that has contributed in some way to this resource. | Coverage | The extent or scope of the content of the resource. For example, this might include location, time, or jurisdiction. | Creator | Person, organization, or service responsible for creating the resource. This typically refers to the resource's author. | Date | A date connected to the resource, such as its last update or its creation date. Recommended practice for encoding the date value is defined in ISO 8601, which follows the YYYY-MM-DD format. | Description | The description of the resource. For example, this might be an abstract, table of contents, or text description of the resource. | Format | The format used for the resource. Usually the format includes the media type or dimensions of the resource. Readers may use Format to determine the software, hardware, or other equipment needed. You usually use a MIME type here. | Identifier | An ID value for the resource in its context. Recommended practice is to identify the resource by means of a string or number as part of a formal identification system. For example, you might use a URI or an International Standard Book Number (ISBN). | Language | The language of the resource. Recommended practice is to use values defined by RFC 1766, which includes a two-letter language code (from the ISO 639 standard) with an optional two-letter country code (from the ISO 3166 standard). | Publisher | The agent responsible for making the resource available. Usually this is a person, an organization, or a service. | Relation | A reference to a related resource or relationship type. | Rights | Rights information about the resource. For example, a Rights element can contain intellectual property rights, copyright, or various other property rights. | Source | A resource from which the current resource is derived. | Subject | The topic of the content of the resource. Recommended practice is to select a value from a formal classification scheme. For example, subjects might be keywords, key phrases, or classification codes. | Title | A name given to the resource. | Type | The type of the content of the resource, usually a term describing general categories or functions. Recommended practice is to select a value from a formally defined and publicly available vocabulary. | Each Dublin Core element also has 10 attributes, which are taken from the ISO/IEC 11179 standard: -
Comment A comment about the use of the data in the element -
Datatype The type of data in the element -
Definition The concept behind the data in the element -
Identifier A unique identifier assigned to the element that identifies it -
Language The language of the data in the element -
Maximum Occurrence A limit on how many times the element may occur -
Name The name you've assigned to the data element -
Obligation Whether the element is required -
Registration Authority The agency or group authorized to register the element -
Version The version of the element In fact, 6 of these 10 attributes are common to all the Dublin Core elements, and they have fixed values. Here they are, along with their values: -
Version : 1.1 -
Registration Authority : Dublin Core Metadata Initiative -
Language : en (that is, English) -
Obligation : Optional -
Datatype : Character String -
Maximum Occurrence : Unlimited The Dublin Core also lists a set of default resource types that you can use with the <Type> element: -
collection -
dataset -
event -
image -
interactive resource -
model -
party -
physical object -
place -
service -
software -
sound -
text |