Error handling of SPARQL query with given RDF graph

Question

I have the following RDF graph with prefixes

PREFIX r: <http://dbpedia.org/resources/>
PREFIX o: <http://dbpedia.org/ontology/>

And the query

PREFIX r: <http://dbpedia.org/resources/>
PREFIX o: <http://dbpedia.org/ontology/>

SELECT ?s ?author
WHERE {
   ?s o:type o:Book .
   ?s o:author ?author .
   ?author ?incategory r:Category:American_atheists.
}

I am now wondering what the output would look like. I have tried using https://dbpedia.org/sparql but this results in a parsing error. Is this a proper query anyway ? The graph has the prefix r for Book and the query has o:Book in the triple.

And you couldn't figure out why the parsing error occurs? The prefixed form of categories doesn't work with an additional colon, i.e. r:Category:American_atheists. is invalid. Either you use the full URI <http://dbpedia.org/resources/Category:American_atheists> you use an additional prefix for the categories, usually it's PREFIX dbc: <http://dbpedia.org/resources/Category:> and then write dbc:American_atheists — UninformedUser
– UninformedUser, Commented Jan 28, 2018 at 13:04
The screenshot is from a textbook, yes? So if this is some kind of exercise, the wrong prefix of book is either a typo or part of the exercise to demonstrate how important using the correct prefix is. — Sentry
– Sentry, Commented Jan 28, 2018 at 13:32
Please consider changing the title of your question. All questions tagged #SPARQL could be generalised with the current title. — Ivo Velitchkov
– Ivo Velitchkov, Commented Jan 28, 2018 at 16:11
Besides the syntax error with the prefix, you have two other issues that cause the empty query. 1) it must be http://dbpedia.org/resource/ 2) it must be rdf:type — UninformedUser
– UninformedUser, Commented Jan 29, 2018 at 3:17
For correctness, yes. Or you can use the Turtle shortcut a, i.e. ?s a o:Book . — UninformedUser
– UninformedUser, Commented Jan 29, 2018 at 11:24

Antoine Zimmermann · Accepted Answer · 2018-02-15 06:43:46Z

3

The parsing error is due to the colon after r:Category. Colon in abbreviated IRIs can only be used as part of the prefix. This query should work:

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX r: <http://dbpedia.org/resource/>
PREFIX o: <http://dbpedia.org/ontology/>

SELECT ?s ?author
WHERE {
  ?s rdf:type o:Book .
  ?s o:author ?author .
  ?author ?incategory <http://dbpedia.org/resource/Category:American_atheists> .
}

Or, if you want a more concise WHERE clause:

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX r: <http://dbpedia.org/resource/>
PREFIX o: <http://dbpedia.org/ontology/>
PREFIX c: <http://dbpedia.org/resource/Category:>

SELECT ?s ?author
WHERE {
  ?s rdf:type o:Book .
  ?s o:author ?author .
  ?author ?incategory c:American_atheists .
}

edited Feb 15, 2018 at 6:43

answered Jan 28, 2018 at 13:06

Antoine Zimmermann

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9 Comments

Carle B. Navy Over a year ago

Thank you! I did not know that. What about the prefix of Book. This causes that you won't get any output (even with proper syntax now), right ?

Sentry Over a year ago

@CarleB.Navy Correct

UninformedUser Over a year ago

o:type is for sure the wrong relation, it must be rdf:type.

UninformedUser Over a year ago

@Sentry No, that's not correct. The prefix for Book is correct, but not for the type relation

UninformedUser Over a year ago

@AntoineZimmermann Can you please fix this: o:type -> rdf:type and http://dbpedia.org/resources/ -> http://dbpedia.org/resource/

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