On 1/8/15 1:53 PM, Mariana Chukanska wrote:
Dear dbpedians,I'm new with sparql and I'm trying to learn it with DBPedia.I want to query i.e. all cloud service platforms from the side: http://dbpedia.org/page/Category:Cloud_platformsand this is the query I use for that in dbpedia snorql: PREFIX dcterms: <http://purl.org/dc/terms/> SELECT ?platform WHERE {{ <http://dbpedia.org/resource/Category:Cloud_platforms> dcterms:subject ?platform.} I will appriciate your suggestions and ideas. Thank you very much for your support in advanced! My very best Marianna
Mairanna,A powerful feature of SPARQL is that it includes the SPARQL Protocol which enables the use of HTTP URIs to identify SPARQL Query Results. In addition, we have an enhancement to the basic SPARQL Protocol URL pattern that enables you substitute the &query parameter with &qtxt, should the recipient of a query results URL want to look at the actual query definition.
Step-by Guide:1. You are interested in what <http://dbpedia.org/resource/Category:Cloud_platforms> identifies 2. You can also obtain a different presentation of what the URI above identifies via <http://dbpedia.org/describe/?uri=http://dbpedia.org/resource/Category:Cloud_platforms> 3. http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbpedia.org&query=SELECT+%3Fplatform%0D%0AWHERE+%7B%0D%0A++++++++%3Fplatform%0D%0A++++++++dcterms%3Asubject+%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FCategory%3ACloud_platforms%3E+.%0D%0A++++++%7D%0D%0A&format=text%2Fhtml&timeout=30000&debug=on -- Query Results Page for all the platforms
4. http://dbpedia.org/c/9CH4UXVL -- shortened version of the above5. http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbpedia.org*&qtxt*=SELECT+%3Fplatform%0D%0AWHERE+%7B%0D%0A++++++++%3Fplatform%0D%0A++++++++dcterms%3Asubject+%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FCategory%3ACloud_platforms%3E+.%0D%0A++++++%7D%0D%0A&format=text%2Fhtml&timeout=30000&debug=on -- Query Definition Page (remember: &qtxt is used instead of &query)
Note:<http://dbpedia.org/resource/Category:Cloud_platforms> is the object (not subject) of the dcterms:subject relation. Even though at first blush it appears to be the opposite since the "is ... of" surrounding the dcterms:subject relation's meaning isn't always clear. Basically, "is .... of" is used as alleviation to quirks in RDF the lead to data being created using triples that take the form:
<http://dbpedia.org/resource/Category:Cloud_platforms> dcterms:subject <http://dbpedia.org/resource/Amazon_Web_Services>
...Because not everyone supports syntax sugar (e.g., what N3 offers) of the form:
<http://dbpedia.org/resource/Amazon_Web_Services> is dcterms:subject of <http://dbpedia.org/resource/Category:Cloud_platforms> .
Anyway, we support the aforementioned N3 syntax sugar too. Hope this helps. -- Regards, Kingsley Idehen Founder & CEO OpenLink Software Company Web: http://www.openlinksw.com Personal Weblog 1: http://kidehen.blogspot.com Personal Weblog 2: http://www.openlinksw.com/blog/~kidehen Twitter Profile: https://twitter.com/kidehen Google+ Profile: https://plus.google.com/+KingsleyIdehen/about LinkedIn Profile: http://www.linkedin.com/in/kidehen Personal WebID: http://kingsley.idehen.net/dataspace/person/kidehen#this
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