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Is it possible to aggregate more than two resources in SPARQL?

Task

In my triple store I have a resource type address. Resources of this type of email have a sender and one or more recipients.

Let the designation "A-> B" be defined as "A is the sender of the email for which B is one of the recipients."

Now I would like to know the following: How many times has a person sent an email to person B? Note that the roles of A and B are important, i.e. A-> B is different from B-> A.

Formatted SPARQL query

To answer this question for all available pairs, I wrote this SPARQL (1.1) query:

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX email: <http://example.com/schema/for/email/> SELECT ?sender ?recipient (COUNT(?sender ?recipient) AS ?count) WHERE { ?sender rdf:type foaf:Person. ?recipient rdf:type foaf:Person. ?e rdf:type email:Email. ?e email:sender ?sender. ?e email:recipient ?recipient. } GROUP BY ?sender ?recipient

This does not work, AllegroGraph gives me the MALFORMED QUERY: Line 5, Found ?recipient (of type varname) error MALFORMED QUERY: Line 5, Found ?recipient (of type varname) - line 5, which is a SELECT clause. I tried other options, changing the SELECT and / or GROUP BY clause, but to no avail.

I'm not sure if aggregates are allowed on multiple resources. In the SPARQL 1.1 documents and the related SO question ( Counting in SPARQL ), I found only aggregates based on one resource.

So finally, here is my question: is it possible to aggregate the sender and receiver?

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1 answer

Try replacing (COUNT(?sender ?recipient) AS ?count) with (COUNT(?e) AS ?count) .

This should work because you want to count the number of emails ( ?e ) that match your criteria.

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Source: https://habr.com/ru/post/1447993/

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