March 27, 2007 12:00 PM
Web 3.0 - 'thing' vocabularies
RDF specifications mention that URI can be used to refer anything that is referred to in a statement. RDF allows use of URI reference (URIref) and fragment identifiers to refer to subject, predicate and object in a statement. RDF uses XML, RDF/XML markup language to represent information in a machine readable format.
The information is structured into a triple <subject, predicate, object>.
Subject – is the 'thing'
Predicate – is the property (characteristics) of the 'thing'
Object – is the value of this property of the 'thing'
The Subject i.e. a 'thing' is identified by an URIref. When an URIref is assigned to a Predicate, by definition of URI it is assumed that this Predicate is a unique property of a 'thing'. Therefore all websites that sell (or refer to) this 'thing' can refer to the same Predicate URIref for this property of the 'thing'. Different web pages may assign different value to this property.
Predicate = Object URIref | literal value.
All web pages that refer to an Object URIref may refer to the same URIref.
This set of URIrefs is known as a vocabulary, this vocabulary is represented by a namespace identifier in a RDF/XML document. The objective and goal of using URIrefs is to migrate towards the use of common vocabularies on the WWW. The access to information with XML pointers and fragment identifiers was limited due to web provider's authority, this scope will be expanded with the use of common vocabulary; information will be accessible within the web provider's authority.
RDF represents a binary relationship between Subject and Predicate.
Example:
Statement: DSL broadband with speed 256Kbps.
Subject = DSL broadband Predicate = speed Object = 256Kbps
This information can be represented in triples as:
xmlns:cdefterms="http://www.commondefinitions.org/terms"
| cdefterms:dsl_broadband | cdefterms:speed | _:br |
| _:br | cdefterms:bitrate | cdefterms:256Kbps |
Here the Advantage of URIref for Predicate 'speed' is that the same URIref can be used for 'speed' property of any 'thing'. The 'speed' property may be vehiclespeed in miles/hr, bitrate in Kbps, Mbps, etc. The web content provider may structure the information according to the speed type applicable for a 'thing'. The Object '256Kbps' may be broken into a triple <cdefterms:_unit cdefterms:Kbps "256">.
RDF specifications suggest that such vocabulary of URIrefs may be used by developers to build applications in accordance with the meaning of these URIrefs. The web page associated with URIrefs may provide semantic information about the term, e.g. if 'speed' is a Predicate, what are the allowed Object values. This information will assist in logical structure design of the information and also provide range checks for the Object values.
Dublin Core Metadata Initiative is a step towards building this vocabulary database. FOAF is another example of RDF OWL implementation by semantic web developers. There is another vocabulary for thread discussions, more can be found such as del.icio.us w3 tags, and others with a comment 'another useful RDF vocabulary'.
The issue to be addressed is "How to control & bring order to the growth of semantic web vocabularies?"
Note: corrected RDF tripple syntax on July 29, 2007.
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