Understanding RDF: the Resource Description Framework in Context (1999)
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Dan Brickley, 3rd European Commission Metadata Workshop, Luxemburg, April 12th 1999 Understanding RDF: the Resource Description Framework in Context http://ilrt.org/discovery/2001/01/understanding-rdf/
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Understanding RDF: the Resource Description Framework in Context (1999)
- 1. Understanding RDF The Resource Description Framework in Context Dan Brickley ILRT, University of Bristol [email_address]
- 8. RDF / Dublin Core example… <?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/1.0/ ” > <rdf:Description about=" http://docs ” > < dc:creator > Joe Smith </ dc:creator > </rdf:Description> </rdf:RDF>
- 10. RDF data model - example
- 11. RDF data model: details... R1 R2 Nodes are resources connected by named properties P1 R1 “ foo” The degenerate case is an arc terminating in a fixed value P1 R1 R2 R3 R6 R4 An RDF description consists of a directed graph of arbitrary complexity R7 R5 R8 P1 P2 P3 P4 P5 P6 P7
- 12. RDF model: one simple idea... (the same idea that underpins the Web) “ The most fundamental specification of Web architecture, while one of the simpler, is that of the Universal Resource Identifier, or URI. The principle that anything, absolutely anything, ‘on the Web’ should identified distinctly is core.” (Tim Berners-Lee) RDF aims to build a Web of overlapping metadata vocabularies We use URIs to define metadata vocabularies We build ‘graphs’ using these vocabularies to say things...
- 18. Getting started… W3C Site: http://www.w3.org/RDF/ RDF-DEV developers list http://www.ilrt.bris.ac.uk/discovery/rdf-dev/ Several RDF parsers now available (Perl, Java...) Netscape / Mozilla RDF implementation http://www.mozilla.org/rdf/doc/ Applications are starting to appear...
Hinweis der Redaktion
- structured babel Often hear talk about prospect of turning the Web into a 'giant database', and that XML is the technology that will enable this. RDF suggests that the crucial technology here is one we've had since the beginning: a universal addressing system, the URI. Analogy: relational database technology is now a desktop commonplace. How do we hook together different tables of information describing different classes of object? Uniquely identifying keys. Simple SQL example: select firstname, surname, street from Person, Address where WorksAt.person_id = Person.person_id and WorksAt.address_id = Address.address_id person_34 --- worksAt---> building_101 -----firstname---> &quot;Dan&quot; -----surname----> &quot;Brickley&quot; building_101 ---street--> &quot;Berkeley Square&quot; Fragmented data is joined through use of reliable identifiers, in this cases, for people and their various addresses. RDF and the Web does exactly the same thing, but on a global scale. The enabling technology here is not a file format but a convention for uniquely identifying objects: the URI. Goals / The Semantic Web promise: data aggregation on a massive scale. RDF's graph data model provides a simple formalism for aggregating data from diverse sources. Simple overlay one graph on top of another. URIs provide a global framework for joining together diverse collections of metadata. Open Issues / challenges /dangers: what is the URI of a person? Of a museum artifact? Of an idea? Of a Web site versus a Web page versus a content or language negotiated rendering of that Web page? Dangers: 'category mistakes' (Ryle 1945) Inspecting URIs: can we tell from inspecting the URI 'http://www.mozilla.org/' whether it refers to a Web page or a Web site? These are two very different objects, each with different properties. Danger of ambiguity: if I decide to use my home page URI or my email address to represent myself in metadata, this may confuse others. If we get this wrong, confusion follows: does 'http://purl.org/net/danbri/' have a size-in-bytes or a weight-in-pounds? Solution: Inscrutable URIs? uuid:342342-2342342-2342342-2342