User Defined Functions (Macros)

RPT supports defining macros in RDF. An IRI with a udf:simpleDefinition property can be used as a function IRI in SPARQL.

The object needs to be an rdf:List, where:

  • The first argument must be a string with a syntactically valid SPARQL expression
  • Any further argument is interpreted as a variable name.

Example

The following example defines a custom eg:greet function that returns Hello X! for an argument X.

# macros.ttl
PREFIX udf: <https://w3id.org/aksw/norse#udf.>
PREFIX sh: <http://www.w3.org/ns/shacl#>
PREFIX eg: <http://www.example.org/>

eg:prefixMapping
  sh:declare [ sh:prefix "afn" ; sh:namespace "http://jena.apache.org/ARQ/function#" ] ;
  .

eg:greet
  sh:prefixes eg:prefixMapping ;
  udf:simpleDefinition ("CONCAT('Hello ', STR(?x), '!')" "x") ;
  .

Using the Macros

Macros are specified using the --macro option and can be used throughout the system, i.e. the CLI arguments, and the SPARQL and GraphQL endpoints.

rpt integrate --macro macros.ttl `SELECT (eg:greet('John Doe') AS ?x) {}` --out-format txt

---------------------
| x                 |
=====================
| "Hello John Doe!" |
---------------------

Notes

  • A current limitation in our implementation is that the sh:namespace presently needs to be a string rather than a literal of type xsd:anyUri, as demanded by the SHACL Specification.
  • Also note, that due to SHACL’s design that the value of sh:namespace needs to be a literal, it is NOT possible to refer to a namespace declared on the document itself:
PREFIX eg: <http://www.example.org/>
PREFIX sh: <http://www.w3.org/ns/shacl#>

eg:prefixMapping
  sh:declare [ sh:prefix "eg" ; sh:namespace eg: ] # Disallowed