Re: RDF in 500 words
Danny here's some free advice. Go build some apps that kick butt. And forget about debates. They don't matter. That's less than 500 words. I bet it's less than 100. Have a nice day. Dave ----- Original Message ----- From: "Danny Ayers" <danny666@v...> To: "Xml-Dev" <xml-dev@l...> Sent: Saturday, November 16, 2002 9:51 AM Subject: RDF in 500 words > There are 6 key documents in the RDF suite, and just the Primer  now runs > to 89 pages of A4. To counter allegations that RDF is altogether too > heavy/complicated/difficult/wordy, I thought I try Andrew's 500 word > challenge on it. > > > -------------------------------- > In RDF, a resource is something that can be identified on the web, and a > description is something said about a resource. > > Resources have a universal identifier, their URI, which in the case of web > pages will be the same as their address (URL). Pretty much anything else > (people, places, concepts) can be identified in this way by assigning URIs. > > Descriptions are made in RDF using statements. A statement has three parts: > the thing being described, the characteristic of interest and the value of > that characteristic. For example, the thing being described might be a book, > say "A Christmas Carol" the characteristic of interest (property) the > author, and the value would be the name of the author, "Charles Dickens". In > RDF jargon these three parts are the subject, predicate and object, and > together they form a triple. The subject is a resource, the predicate is a > special kind of resource and the object can either be another resource or > literal text. > > As a resources, the predicates are also unambiguously identified using URIs, > but the same predicate can be reused - when we ask who the author of a book > is, we are asking the same question whichever book we are talking about or > whoever happens to be the author. If we want to say more about a particular > book, we can use its identifier in another statement with a different > predicate (property) and object (value). The basic nature of resources and > predicates are defined with the help of a small set of terms in the RDF > specifications. This set of terms allows us to give more information in our > descriptions, so we could define a classification 'paperback' and say that > this is a kind of book. The class 'book' would in turn be described as a > kind of resource. > > In this example we have identified the author by the text of their name, but > usually it is more useful to use a URI as that will be unambiguous, and > allow us to say things about the author as well. So we could have another > statement that says that this author's favourite colour is blue. Our > knowledge can be expressed as these two statements, but as the author is a > common feature in this we can visualise the knowledge as the three resources > linked by the connection from the book to the author and from the author to > the colour blue. This structure is an example of an RDF graph. There may be > other resources that we can link in as well, like books by the same author > or the book's publisher. > > It isn't entirely always necessary or even possible to identify resources. > Let's say we have identified the book and the colour blue. We can still make > two statements, "A Christmas Carol" was written by X, and the X's > favourite colour is blue. This can still be visualised as a graph with three > items and two connections, and in the jargon X is known as a blank node. > > seeAlso: http://w3.org/RDF > ----------------------------------- > > Cheers, > Danny. > >  http://www.w3.org/TR/2002/WD-rdf-primer-20021111/ > > ----------- > Danny Ayers > > Semantic Web Log : > http://www.citnames.com/blog > > > > ----------------------------------------------------------------- > The xml-dev list is sponsored by XML.org <http://www.xml.org>, an > initiative of OASIS <http://www.oasis-open.org> > > The list archives are at http://lists.xml.org/archives/xml-dev/ > > To subscribe or unsubscribe from this list use the subscription > manager: <http://lists.xml.org/ob/adm.pl> >
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