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POMultiple aggregates in SPARQL
 

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    <p>I have a triple store that contains mail archive data. So let's say I have a lot of persons (<code>foaf:Person</code>) that have sent (<code>ex:hasSent</code>) and received (<code>ex:hasReceived</code>) emails (<code>ex:Email</code>).</p> <p>Example:</p> <pre><code>SELECT ?person ?email WHERE { ?email rdf:type ex:Email. ?person rdf:type foaf:Person; ex:hasSent ?email. } </code></pre> <p>The same works for <code>ex:hasReceived</code>, of course. Now I would like to do some statistics and analytics, i.e. determine how many emails an individual has sent and received. Doing this for only one predicate is a simple aggregation:</p> <pre><code>SELECT ?person (COUNT(?email) AS ?count) WHERE { ?email rdf:type ex:Email. ?person rdf:type foaf:Person; ex:hasSent ?email. } GROUP BY ?person </code></pre> <p>However, I need need the number of received emails as well and I would like to do this without having to issue a separate query. So I tried the following:</p> <pre><code>SELECT ?person (COUNT(?email1) AS ?sent_emails) (COUNT(?email2) AS ?received_emails) WHERE { ?person rdf:type foaf:Person. ?sent_email rdf:type ex:Email. ?person ex:hasSent ?sent_email. ?received_email rdf:type ex:Email. ?person ex:hasReceived ?received_email. } GROUP BY ?person </code></pre> <p>This did not seem to be right, as the numbers for the emails sent vs. received were exactly the same. I assume this is because my SPARQL statement results in a cross product of all mails a person has ever sent and received, right?</p> <p>What do I need to do in order to get the statistics right on a per-individual basis?</p>
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