I'd like to know how to submit a SPARQL query to DDBpedia and be given back a table that includes the information found in the Wikipedia "chembox" info box template, such as molecular weight or formula.
So, the first step was just to make a query whose results should be a list of chemical substances that had the formula and molecularWeight properties included. But the following returns no results:
SELECT * WHERE {
?y rdf:type dbpedia-owl:ChemicalSubstance.
?y rdfs:label ?Name .
?y dbpedia:molecularWeight ?molecularWeight .
?y dbpedia:formula ?formula .
OPTIONAL {?y dbpedia-owl:iupacName ?iupacname} .
FILTER (langMatches(lang(?Name),"en"))
}
LIMIT 50
SPARQL Explorer at dbpedia.org
And so I'm stuck. Is something wrong with this query or does DBPedia really not collect that information from the Wikipedia chemboxes?
You caught the wrong namespace for both dbpedia:molecularWeight and dbpedia:formula. The correct namespace here would be dbpedia2.
Furthermore, there seem rarely any entries having a dbpedia-owl:iupacName, dbpedia2:molecularWeight and dbpedia2:formula.
SELECT * WHERE {
?y rdf:type dbpedia-owl:ChemicalSubstance.
?y rdfs:label ?Name .
OPTIONAL {?y dbpedia2:formula ?formula }.
OPTIONAL {?y dbpedia2:molecularWeight ?molecularWeight}.
OPTIONAL {?y dbpedia-owl:iupacName ?iupacname} .
FILTER (langMatches(lang(?Name),"en"))
}
LIMIT 50
To get the correct namespaces, you could either look at one example like this or get a list of all used properties for type dbpedia-owl:ChemicalSubstance using
SELECT DISTINCT ?rel WHERE {
?y rdf:type dbpedia-owl:ChemicalSubstance.
?y ?rel ?x
}