RDF is a graph based data format (serialised to XML). It is based on triples. Such as: Peter hasParent Paal. To query RDF, we use the graph query language SPAR

RDF is a graph based data format (serialised to XML). It is based on triples. Such as: Peter hasParent Paal. To query RDF, we use the graph query language SPARQL. You create a graph with variables in it, and the query engine will find subgraphs that match the graph. On top of this we can do reasoning (based on 1st order logics and datalog). With RDFS (simple) and OWL (advanced). And to bring all this together there are many open vocabularies and open data sets linked together. One notable one: DBpedia (based on wikipedia). A grand view of linked data: http://lod-cloud.net/versions/2011-09-19/lod-cloud.html http://lod-cloud.net/versions/2011-09-19/lod-cloud.html A sample SPARQL query on DBpedia listing software by date: http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbpedia.org&query=select+%3Fa+min%28%3Fb%29+%28min%28%3Fdate%29+as+%3Fdate2%29+where+%7B%0D%0A%0D%0A%3Fa+a+dbpedia-owl%3ASoftware%3B%0D%0A+rdfs%3Alabel+%3Fb%3B%0D%0Adbpedia-owl%3AlatestReleaseDate+%3Fdate.%0D%0A%0D%0A%0D%0A%0D%0A%7D+%0D%0Agroup+by+%3Fa%0D%0Aorder+by+%3Fdate2%0D%0ALIMIT+100&format=text%2Fhtml&timeout=0&debug=on http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbp... The actual query: select ?a min(?b) (min(?date) as ?date2) where { ?a a dbpedia-owl:Software; rdfs:label ?b; dbpedia-owl:latestReleaseDate ?date. } group by ?a order by ?date2 LIMIT 100