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The IMesh Toolkit
[ Work In Hand > Technology Review > Standards and Protocols ]
Resource Description Framework (RDF) |
Overall Purpose |
| The RDF provides a framework for the description, process and ultimately interchange of metadata. RDF metadata can be used in a variety of application areas; for example: in resource discovery to provide better search engine capabilities, in cataloguing , in content rating and in describing collections of pages that represent a single logical "document" and description of intellectual property rights. It can be used by intelligent software agents to facilitate knowledge sharing and exchange [1]. RDF supports vocabularies that are both human- and machine-readable, a characteristic that is likely to enhance its adoption by resource description communities. Additionally the schema specification version 1.0 has included an extensibility mechanism to allow for additions to the RDF. That is, it provides some additional facilities to support the evolution of individual RDF vocabularies, as well as that of the core Schema specification vocabulary. |
Brief Overview of Functionality |
| The use of URI's to name vocabularies is an
important design feature of RDF; many previous metadata
standardization efforts in other areas have foundered on the
issue of establishing a central attribute registry. [4] Another
feature of proposed extensibility is the anticipation of RDF
content drawing upon properties or classes which were defined
using constraints other than those currently available; in other
words there is a recognition that presently unknown constraints
may form in the future a more expressive framework for specifying
RDF constraints [2].
The basis of the RDF is one of statements: these comprise firstly the resource described, identified by the a URI, a named property, which is a defined attribute or relation, and the value of that named property, either a string or another resource, (in other words like an attribute pair of attribute and value). The syntax of these statements is XML which allows for RDF properties to be easily interchanged [3] . RDF also employs the XML Namespace facility to identify the schema in which the properties and classes are defined. The resources described can be of any type, both XML and non-XML resources. |
Deployment |
| The advantage or otherwise of employing RDF
depends almost entirely on its perceived usefulness or otherwise
in relation to XML or, conceivably HTML. With regard to XML, it
might be argued XML documents should be a natural vehicle for
exchanging general purpose metadata. XML, however, it can be
equally argued, falls down in terms of scalability.
Firstly, the order in which elements appear in an XML document is significant and often very meaningful and in the metadata context appears strange to some. Furthermore, maintaining the correct order of millions of data items is in practice difficult and costly. Secondly, when XML documents are represented in computer memory, strange data structures mixing trees, graphs, and character strings are obtained. In general, these are hard to handle in even moderate amounts, let alone on the grand scale. XML is unequalled as an exchange format on the Web; but alone, it is argued, it fails to provide what is needed in a metadata framework [4] . The question that does arise is whether RDF is as essential as XML appears to be: given reservations existing over RDF, is there not the alternative of the adoption of XML schemas? The key feature claimed for RDF is its flexibility, given that users can invent properties for the resources they are describing. There is much debate as to how wise it would be to place a strait-jacket on such independence in the form of an over-restrictive standard. What is claimed for RDF is that those engaged in resource description are encouraged to concentrate on its semantics rather than the metadata syntax or structure. Indeed one broad and laudable aim would be to hide the workings of RDF as much as possible and so increase its accessibility. Further, the RDF schema specification language may be seen as less expressive than others, but is much simpler to implement. However RDF's status is still that of an emerging standard. A perceived weakness of RDF at the moment is that there is insufficient software support. On the other hand the interest from large web browser vendors gives some participants hope that large scale deployment of tools which understand about RDF will take place; this, it is claimed in turn should lead to the widespread adoption of RDF on the web [5] . |
Related Standards |
| XML [UKOLN XML review]
XML is the principal related standard given that RDF is expressed in XML and st ructures XML although RDF can also be expressed in HTML, albeit in a simple form. |
Relevance to IMesh context |
| Moreover the usefulness of RDF in the description of Web resources coincides with one of the objectives of the Dublin Core Metadata Initiative [6] and consequently enhances its relevance in the context of employing Dublin Core. Ultimately however, the adoption of RDF would wait upon the decision as to whether, on the assumption XML is the syntax of choice, XML schemas approach attracts greater support than RDF. |
References |
| [1] RDF Overview, W3C Technology and
Society Domain http://www.w3.org/RDF/ [2] W3C Candidate Recommendation 27 March 2000: RDF Schema Specification 1.0 (work in progress) Editors: Dan Brickley, University of Bristol , R.V. Guha, Epinions http://www.w3.org/TR/2000/CR-rdf-schema-20000327 [3] Renardus Project Technical Standards Report http://nwi.dtv.dk/RENARDUS/D2.1/RDF.html#S3 [4] What is RDF? Tim Bray, Technical Editor, XML.com. and co-editor of the XML specification. January 2000. http://www.xml.com/pub/a/2001/01/24/rdf.html [5] Introduction to RDF Metadata, W3C NOTE 1997-11-13, Ora Lassila, Nokia Research Center http://www.w3.org/TR/NOTE-rdf-simple-intro-971113.html [6] Dublin Core Metadata Initiative http://purl.oclc.org/dc/ |
Other Standards and Protocols |
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| CIP | DC | LDAP | OAI |
| RDF | RSS | SDLIP | SOAP |
| WHOIS++ | XHTML | XML | Z39.50 |