Add sh:SPARQLFunction

[HolgerKnublauch]

SHACL-AF include vocabulary to declare new (SPARQL) functions: https://w3c.github.io/shacl/shacl-af/#functions

The SHACL-SPARQL 1.2 spec should include this feature. In TopBraid we have supported this for many years and it has proven to be very useful for encapsulating reusable query snippets.

[tpluscode]

I have been thinking about function expressions and their relation to SPARQL.

SHACL-AF also has the Function Expression and https://datashapes.org/sparql# exists which defines many sh:Function (not sh:SPARQLFunction, despite its name)

IMO, we should have a more generalised set of function expressions (as in the dash-sparql namespace) which can be implemented and executed both with and without SPARQL.

The role of SHACL-SPARQL would then be to defined how each such function is implemented with SPARQL (if supported)