Easiest way to query if a name exists in Wikidata? - sparql

Question

I'm trying to create the simplest possible query to check if a name exists in Wikidata. For example, I just to want to see if the common name "Jack Smith" is in Wikidata.
Following the example query in this StackOverflow answer, I created the following SPARQL query (run it):
SELECT distinct ?item ?itemLabel ?itemDescription WHERE{
?item ?label "Jack Smith" .
?article schema:about ?item .
?article schema:inLanguage "en" .
?article schema:isPartOf <https://en.wikipedia.org/>.
SERVICE wikibase:label { bd:serviceParam wikibase:language "en". }
} LIMIT 10
However, it returns zero results.
On the other hand, if I search for "Jack Smith" through the Wikidata search webpage, I get back 1200+ results with a lot of people named "Jack Smith".
The behavior with the SPARQL interface is inconsistent. When I run a SPARQL search for "Abraham Lincoln" (run it), I correctly get back an entry for the American president by that name.
My specific questions are:
Why is my SPARQL query returning zero results for "Jack Smith"?
What is the simplest API call to check if a name (e.g. Jack Smith) exists in Wikidata? It could be SPARQL or some other REST API.
Thank you.

Answer 1

The query returns zero results because there is no Jack Smith about whom there is an article in English and is part of Wikipedia.org.
Every line in the body of a SPARQL query is a way to restrict the search as opposed to just a way to add new variables.
Look at this query:
SELECT ?person ?dateOfDeath
WHERE {
?person a :Person .
?person :date_of_death ?dateOfDeath .
}
This would only return people who have a date of death, i.e. who are dead, as well as the date.
If you wanted to return people, and optionally their date of death, i.e. if they are still alive, you don't want a date, but you do want the person, then use this:
SELECT ?person ?dateOfDeath
WHERE {
?person a :Person .
OPTIONAL {?person :date_of_death ?dateOfDeath }
}
In terms of your second question, I'd try something like this:
SELECT ?boolean
WHERE{
BIND(EXISTS{?item ?label "Jack Smith"} AS ?boolean)
}
This can of course also be issued as, say, a cURL request:
curl https://query.wikidata.org/bigdata/namespace/wdq/sparql -X POST --data 'query=SELECT%20%3Fboolean%0AWHERE%7B%0ABIND%28EXISTS%7B%3Fitem%20%3Flabel%20%22Jack%20Smith%22%7D%20AS%20%3Fboolean%29%0A%20%20%7D'