shite

shite is a tiny macro language for SHACL that implements conditionals.

The acronym shite stands for SHacle If Then Else. If you read it as an apronym, that's on you. 🤭

Concept

shite defines a meta-shapes graph that is meant to be run against a shapes graph by a SHACL processor. Note that shite requires a SHACL processor that supports sh:SPARQLRule from SHACL Advanced Features.

The general idea of shite is to introduce a vocabulary for if-then-else that macro-transforms to the respective and-or-not expressions.

shite defines

1. conditional terms shite:if, shite:then and shite:else
2. a grammar for if-then-else enforced by SHACL shapes
3. macro-expander shapes that transform shite terms into sh:and/sh:or/sh:not constructs

Example

The following SHACL shapes graph uses shite terms to define conditional constraints such that, if the target node has <urn:x> asserted about it, it must also have <urn:y> asserted about it; else, it must have <urn:z> asserted about it.

@prefix ex: <http://example.org#> .
@prefix shite: <https://github.com/lu-pl/shite#> .
@prefix sh: <http://www.w3.org/ns/shacl#> .

ex:Shape a sh:NodeShape ;
	sh:targetNode <urn:target> ;
	shite:if [
		sh:property [
			sh:path <urn:x> ;
			sh:minCount 1 ;
			sh:maxCount 1
			]
		] ;
	shite:then [
		sh:property [
			sh:path <urn:y> ;
			sh:minCount 1 ;
			sh:maxCount 1
			]
		] ;

	shite:else [
		sh:property [
			sh:path <urn:z> ;
			sh:minCount 1 ;
			sh:maxCount 1
			]
		] .

Running a SHACL AF processor with shite as the shapes graph and the above SHACL graph as the data graph validates and expands the given shite terms and transforms the data graph like so:

@prefix ex: <http://example.org#> .
@prefix shite: <https://github.com/lu-pl/shite#> .
@prefix sh: <http://www.w3.org/ns/shacl#> .

ex:Shape a sh:NodeShape ;
	sh:targetNode <urn:target> ;
	sh:or (
		[
			sh:not [
				sh:property [
					sh:minCount 1 ;
					sh:maxCount 1 ;
					sh:path <urn:x>
					]
			]
		]
		[
			sh:property [
				sh:minCount 1 ;
				sh:maxCount 1 ;
				sh:path <urn:y>
				]
		]
	),
	(
		[
			sh:property [
				sh:minCount 1 ;
				sh:maxCount 1 ;
				sh:path <urn:x>
			]
		]
		[
			sh:property [
				sh:minCount 1 ;
				sh:maxCount 1 ;
				sh:path <urn:z>
			]
		]
	) .

The expanded data graph can then be used as a shapes graph to validate another data graph.

According to the above expansion, the following validates

<urn:target> <urn:x> "literal" ;
	<urn:y> "other literal" .

<urn:target> <urn:z> "yet another literal" .

<urn:target> <urn:y> "other liteal" ;
	<urn:z> "yet another literal" .

while the triples below do not pass validation:

<urn:target> <urn:x> "literal" .

<urn:target> <urn:y> "other literal" .

<urn:target> <urn:x> "literal" ;
	<urn:z> "yet another literal" .