How to access child properties using Wikidata SPARQL Query Service? - sparql

Question

I would like to access child properties of wikidata entities. An example may be property P1033, which is a child of P4952, for an entity such as Q49546. How can I do this dynamically in a SPARQL query?
Using the query builder provided by the online Wikidata Query Service, I can construct a simple query, which works for normal properties (in the linked example: mass), but not for the desired sub-properties (in the linked example: NPFA-code for health hazard), which end up empty, even though they are clearly set in the web-result. Side-note: it is a different example than the one from the first paragraph.
The desired objective is the dynamic query as follows:
SELECT ?p ?item ?itemDescription ?prop ?value ?valueLabel ?itemLabel ?itemAltLabel ?propLabel WHERE {
BIND(wd:Q138809 AS ?item)
?prop wikibase:directClaim ?p.
#?item ?p ?value.
SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en".
?value rdfs:label ?valueLabel.
?prop rdfs:label ?propLabel.
?item rdfs:label ?itemLabel;
skos:altLabel ?itemAltLabel;
schema:description ?itemDescription.
}
}
ORDER BY DESC(?prop)
LIMIT 10
With the line 4 as a comment, I can get my propLabel as desired, but no value; doing it the other way round with the line not as comment, I do get only the properties, which are set on first level, but not the child properties.

Answer 1

Thanks to #AKSW, I herewith post the final query solving my problem:
SELECT ?item ?itemLabel ?itemDescription ?itemAltLabel ?prop ?propertyLabel ?propertyValue ?propertyValueLabel ?qualifier ?qualifierLabel ?qualifierValue
{
VALUES (?item) {(wd:Q138809)}
?item ?prop ?statement .
?statement ?ps ?propertyValue .
?property wikibase:claim ?prop .
?property wikibase:statementProperty ?ps .
OPTIONAL { ?statement ?pq ?qualifierValue . ?qualifier wikibase:qualifier ?pq . }
SERVICE wikibase:label { bd:serviceParam wikibase:language "en" }
}
The key step for me was to understand that child properties are actually called qualifiers.