Virtuoso Open-Source Edition

  • Topic
  • Discussion

    • 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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