Custom calculator function

[ch-sander]

Suppose I want to display certain mathematical functions as a value in a separate column in the query result that cannot be defined dynamically by the user in the aggregate widget. Can I define a class with a SPARQL query that performs the calculation and returns the result as a number?

Imagine I want the logarithm or some specific fraction calculated on the basis of some domain URI, e.g. the number of sentences divided by the number of pages in some book. The
BOOK URI would be the domain and SENTENCES PER PAGE the property, the result a XSD:DECIMAL. So, the table should have the columns BOOK and SENTENCES PER PAGE.

[ch-sander]

Pseudocode

PREFIX grace: <http://www.graceful17.org/ontology/>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

SELECT ?book ?sentences ?pages ?sentencesPerPage WHERE {
  ?book a grace:Book ;
        grace:numberOfSentences ?sentences ;
        grace:numberOfPages ?pages .
  
  BIND(xsd:decimal(?sentences) / xsd:decimal(?pages) AS ?sentencesPerPage)
}

[ch-sander]

I might be wrong but custom data sources seem to cover only object properties, not literals, as range.

But I imagine that there is a runtime variable that could bind ?sentencesPerPage so that a numeral being returned as literal.

[tfrancart]

Suppose I want to display certain mathematical functions as a value in a separate column in the query result that cannot be defined dynamically by the user in the aggregate widget. Can I define a class with a SPARQL query that performs the calculation and returns the result as a number?

No. This is clearly out of scope of what Sparnatural can do. We are not trying to cover 100% of SPARQL; there is currently no plan to support this.

I might be wrong but custom data sources seem to cover only object properties, not literals, as range.
But I imagine that there is a runtime variable that could bind ?sentencesPerPage so that a numeral being returned as literal.

Yes, you can write a custom datasource that returns a literal. And yes, you can use a BIND and do some calculation in this custom datasource. But this will not allow a user to do this calculation in the final query.
The documentation on datasources does not cover how to return a literal, and it needs to be updated. I will create a separate issue. To do this the SPARQL query needs to return the variables ?value and ?label instead of ?uri and ?label

[ch-sander]

I think I found the function in the JavaScript that replaces $this with the sparqlString for a class or property, but I couldn't find a function that allowed to change the syntax of the pattern to allow for a BIND statement so that the original object of the triple is bound.

I also realized that in the yasgui plugins library exist many custom calculation functions that don't seem to be included in the aggregate widget either, but I didn't look closely, tbh.

[ch-sander]

Great.
I didn't mean to allow the user to define the function or calculation but just to call it via UI.