How to use aggregate function like SUM in marklogic sparql query with triples?

Question

I have following triples :

<?xml  version="1.0" encoding="UTF-8"?>
<sem:triples xmlns:sem="http://marklogic.com/semantics">
  <sem:triple>
    <sem:subject>item1</sem:subject>
    <sem:predicate>hasQty</sem:predicate>
    <sem:object>20</sem:object>
  </sem:triple>
</sem:triples>


<?xml  version="1.0" encoding="UTF-8"?>
<sem:triples xmlns:sem="http://marklogic.com/semantics">
  <sem:triple>
    <sem:subject>item2</sem:subject>
    <sem:predicate>hasQty</sem:predicate>
    <sem:object>5</sem:object>
  </sem:triple>
</sem:triples>`

This is the SPARQL query I am using to calculate sum of these quantities:

select (SUM(?p) as ?p) where { ?s <hasQty> ?p}

And the result I get is this -> "0"^^xs:integer instead of 25. Can you please suggest what is wrong in this.

Answer 1

Marklogic is a very powerful and versatile tool. Having said that, the way it handles RDF & SPARQL is at least a little non-standard in my opinion.

In the future, you could probably read this: https://docs.marklogic.com/sem:rdf-serialize to learn how to convert MarkLogic's native representation of triples into standard RDF.

Now I'm not an XML expert, but I don't think your triples block is valid XML. If it were, you could write an XSLT transformation to turn it into RDF XML.

I did a little manual tidying to get well-formed XML, mainly for illustration purposes:

<?xml version="1.0" encoding="UTF-8"?>
<sem:triples xmlns:sem="http://marklogic.com/semantics">
  <sem:triple>
    <sem:subject>item1</sem:subject>
    <sem:predicate>hasQty</sem:predicate>
    <sem:object>20</sem:object>
  </sem:triple>
  <sem:triple>
    <sem:subject>item2</sem:subject>
    <sem:predicate>hasQty</sem:predicate>
    <sem:object>5</sem:object>
  </sem:triple>
</sem:triples>

As RDF/XML, that might look something like

<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF
        xmlns="http://wanna.be/"
        xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">

<rdf:Description rdf:about="http://wanna.be/item1">
        <hasQty>20</hasQty>
</rdf:Description>

<rdf:Description rdf:about="http://wanna.be/item2">
        <hasQty>5</hasQty>
</rdf:Description>

</rdf:RDF>

I created a default namespace of http://wanna.be/, and you can use the default abbreviation to say :hasQty instead of http://wanna.be/hasQty It's a little unusual to use a bare word like <hasQty> as a URI for a term in SPARQL query.

Therefore, to get the sum of quantities, cast each quantity string to an int and then sum:

PREFIX : <http://wanna.be/>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
select (sum(xsd:int(?o)) as ?oSum)  where {?s :hasQty ?o}