How to properly use SPARQL OPTIONAL to retrieve attributes for a resource that may exist? - sparql

Question

I'm trying to use a SPARQL query to retrieve information about a DBpedia resource (a Person). I'd like to use the same query to retrieve data about any Person by parameterizing the resource URI. Since some attributes may not exist for a particular resource, I'm making use of the OPTIONAL statement. Here is my query:
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX dbpprop: <http://dbpedia.org/property/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT DISTINCT ?label ?abstract ?placeOfBirth
?birthPlace ?birthDate ?deathDate ?page ?thumbnail
WHERE {
<http://dbpedia.org/resource/Neil_Simon> rdfs:label ?label ;
dbo:abstract ?abstract ;
foaf:page ?page .
OPTIONAL {
<http://dbpedia.org/resource/Neil_Simon> dbpprop:placeOfBirth ?placeOfBirth ;
dbpprop:birthPlace ?birthPlace ;
dbo:birthDate ?birthDate ;
dbo:deathdate ?deathDate ;
dbo:thumbnail ?thumbnail .
}
FILTER (LANG(?label) = 'en')
FILTER (LANG(?abstract) = 'en')
}
LIMIT 1
I've left everything except label, abstract and page in OPTIONAL, since if I use the same query for another person, they may not have those properties. The problem is, none of those optional attributes are showing up in the results. In Neil Simon's case, you can see that there are values for birthDate, birthPlace and thumbnail: http://dbpedia.org/resource/Neil_Simon. However, those values don't show up when I run the query: DBpedia SPARQL query. What am I doing wrong, and how can I optionally retrieve those properties?

Answer 1

Although you have used an OPTIONAL construct the map pattern itself needs all the attributes within to match. So only if you have birthPlace, birthDate, deathDate and thumbnail the inner optional construct is satisfied
I would suggest breaking the OPTIONAL construct up into multiple OPTIONAL constructs.