Generate a JSON schema

JSON Schema generation from SHACL

The algorithm follow these steps to generate the JSON Schema:

Constant declarations

• A declaration is always added for @context since we are targeting JSON-LD
• schema version is always set to https://json-schema.org/draft/2020-12/schema
• a container_language declaration is always added with a patternProperty declaration with properties being language codes to deal with "@container": "language" properties.

Schema header

• title is populated from an owl:Ontology dct:title or rdfs:label
• version is populated from an owl:Ontology owl:versionInfo
• description is populated from an owl:Ontology dct:description

Node shapes conversion

Each node shape with at least one non-deactivated property shape is turned into an object schema in the $defs section of the schema, with the URI local name as the name of the schema. Node shapes with no non-deactivated property shapes are turned into string schemas being simple iri-reference.

• title is populated from the node shape rdfs:label
• description is populated from the node shape rdfs:comment
• There is always a required id property
• If there is an sh:pattern associated to the node shape, it is turned into a pattern constraint on the id key
• If there is a skos:example associated to the node shape, it is turned into an example constraint on the id key
• If node shape is closed, then additionalProperties is set to false, except if the flag "never set additional properties" is set.
• Then each property shape is processed as described below

Property shapes conversion

Non-deactivated property shapes are processed this way:

• If a JSON-LD context was provided, it is probed to determine the term for the property. The context probing works if it matches the property @type in the context (either an @id property, or the datatype for literal properties).
• If context was not provided, the corresponding JSON key is read from shacl-play:shortName annotation, otherwise the local name of the property in sh:path is used as the JSON key
• title is populated from the property shape sh:name
• description is populated from the property shape sh:description
• The property shape is mapped to a schema this way:
  • If the property shape has an sh:hasValue, a const schema is created with the value. If a JSON-LD context was provided, an attempt is made to simplify the value to its actual mapping from the context, either because it is directly declared in the vocab, or because a prefix is declared.
  • If the property shape has an sh:in, an enum schema is created with the list of possible values. If a JSON-LD context was provided, an attempt is made to simplify the list of possible values to their actual mapping from the context, either because they are directly declared in the vocab, or because a prefix is declared.
  • If the property shape has an sh:pattern, a string schema is generated with a pattern constraint. If a JSON-LD context was provided, the pattern constraint is "reduced" so that patterns matching complete IRIs may match only the end of IRI if they are shortened due to @base in the context
  • If the property shape has an sh:node, then :
    • If the property shape is annotated with shacl-play:embed shacl-play:EmbedNever, then a string schema with format iri-reference is generated
    • Otherwise, create a $ref schema with a reference to one of the schemas in the #/$defs section
    • Then the algorithm determines whether the property requires an array:
      • If a JSON-LD context was provided, try to compact a test of the property to determine if the context mandates a @container : @set. If the compaction test returns an array, then an array will be declared in the output schema
      • Otherwise, if there is a sh:qualifiedMaxCount and it is > 1, then wrap the generated schema into an array schema
      • Otherwise, if there is no sh:maxCount or a sh:maxCount that is > 1, then wrap the generated schema into an array schema
  • If the property shape has an sh:pattern, then turn it into a string schema with a pattern constraint.
  • If the property shape has an sh:datatype, or an sh:qualifiedValueShape that has an sh:datatype then:
    • If it is rdf:langString, then make a reference to the container_language in the #/$defs section
    • Create a string, boolean or numeric schema according to the datatype-to-schema mapping
  • If the property shape has an sh:nodeKind pointing to sh:IRI, generate a string schema of format iri-reference.
  • Otherwise, return an empty schema
• If the sh:minCount, or the sh:qualifiedMinCount of the property is > 0, the JSON key is added to the list of requiredProperties of the schema

Root node shape

With the provided root node shape IRI, create a reference to the corresponding schema from the #/$defs section.