Are custom SPARQL extension functions supported? How can I use them?

Virtuoso supports two ways to write one's own custom SPARQL extension functions:

Use a Stored Procedure

You can create a SQL stored procedure in Virtuoso PL and, call it using the sql: prefix: 


SQL> CREATE PROCEDURE testfunc()
  {
    -- your code here
  }
;

Done;

SQL> SPARQL 
SELECT * 
  WHERE
    { 
      ?s  ?p  `sql:testfunc(?o)` 
    };

For more details see Calling SQL from SPARQL Virtuoso Documentation.

Create a built-in function

You can also make a built-in function, which is basically a C function that can be called from both SQL and SPARQL, as in the example from below, using the bif: prefix.

In this SPARQL example, we use the CONTAINS function to do a freetext search on all ?o that contain words starting with "Timo".


SELECT * 
  FROM <http://www.w3.org/people#> 
  WHERE 
    { 
      ?s  ?p            ?o         . 
      ?o  bif:contains  '"Timo*"'
    }

For more details see Using Full Text Search in SPARQL Virtuoso Documentation.

This feature also allows you to use relevant functions from the Virtuoso SQL Functions Guide inside a SPARQL query.

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