Class Node

A Class Node is used as a potential range for a Property Node.

It is represented by an object with "@type": "sh:NodeShape" that is wrapped by the term sh:node. This NodeShape is used to express all the characteristics and constraints of the Class Node. The most important constraint is sh:class, which constraints the class(es) that the target entity must have. For sh:class arrays are allowed, which are supposed to represent multi-typed entities (MTE).

The @id of a Class Node is used to reference it in other parts of the Domain Specification, and so reuse already defined constraints for a specific Class. Details below.

1. Example

{
  "sh:node": {
    "@id": "https://semantify.it/ds/OBbzsh4_B#DpruH",
    "@type": "sh:NodeShape",
    "sh:class": [
      "schema:Airport"
    ],
    "sh:closed": true,
    "sh:property": [
      ...
    ]
  }
}

2. Key-value Table

The following table lists all possible terms that can be used by a Class Node. The order in the table reflects the recommended order of these terms within a Class Node (optional).

key	required	value type	description	related error
@id	true	IRI	The IRI of the Class Node, which is based on the DS IRI it is in
@type	true	"sh:NodeShape"	The fixed type for a Class Node
sh:class	true	[ IRI ]	The IRI(s) of the Class(es) that the entity must have	Non-conform range
sh:closed	false	Boolean	Specifies if additional properties are allowed or not	Non-conform property
sh:property	false	List of PropertyNode	A list of property nodes that apply to the entity	Missing Property, Non-conform Property

3. Semantics

3.1. Class-Matching

See SHACL specification.

A Class Node includes sh:class to specify the class(es) that the verified entity MUST match. Domain Specifications use custom semantics for class matching.

Examples:

"sh:class": [
  "schema:LodgingBusiness",
  "schema:Restaurant
]

"sh:class": [
  "schema:Article"
]

3.2. Properties

The terms sh:property and sh:closed are used in a Class Node to give further restrictions on the properties of the corresponding entity. Such a Class Node with property restrictions is also called Restricted Class Node. A Class Node without further property restrictions is called a Standard Class Node.

3.2.1. sh:property

See SHACL specification.

The term sh:property lists the property shapes that the target entity must comply with. For every property, there is a corresponding Property Node in this list.

Example:

"sh:property": [
  {
    "@type": "sh:PropertyShape",
    "sh:order": 0,
    "sh:path": "schema:identifier"
    "sh:maxCount": 1,
    "sh:or": [
      {
        "sh:datatype": "xsd:string",
      }
    ]
  },
  {
    "@type": "sh:PropertyShape",
    "sh:order": 1,
    "sh:path": "schema:alternateName"
    "sh:maxCount": 1,
    "sh:or": [
      {
       "sh:datatype": "xsd:string",
      }
    ]
  }
]

3.2.2. sh:closed

See SHACL specification.

The term sh:closed can be used to specify if additional properties (other than the properties allowed by sh:property) are allowed or not. In the past, Domain Specifications had "sh:closed": true implicitly in all NodeShapes. Now the DS creator should specify the wished behaviour.

Example:

"sh:closed": true

3.3. Use of Internal references

In order to reference NodeShapes that are part of a DS, those NodeShapes need an IRI. It makes sense to give them the same BaseIRI as the DS in which they are in, with the addition of a fragment id, e.g. in the DS with the IRI https://semantify.it/ds/OBbzsh4_B there could be a NodeShape with the IRI https://semantify.it/ds/OBbzsh4_B#DpruH.

Example Class Node (inner NodeShape):

{
  "sh:node": {
    "@id": "https://semantify.it/ds/OBbzsh4_B#DpruH",
    "@type": "sh:NodeShape",
    "sh:class": ["schema:PostalAddress"],
    "sh:closed": true,
    "sh:property": [
      ...
    ]
  }
}

Example Property node that references the previous example Class node:

{
  "@type": "sh:PropertyShape",
  "sh:path": "schema:address",
  "sh:or": [
    {
      "sh:node": {
        "@id": "https://semantify.it/ds/OBbzsh4_B#DpruH"
      }
    }
  ]
}

In order to make the use of internal references more convenient, we introduce the following rules:

• Every NodeShape inside a DS receives an IRI, even if it hasn't been referenced yet.

• The NodeShape that specifies the class node (the referenced NodeShape) contains "@type": "sh:NodeShape" and all the constraints needed.

• The internal references contain only the @id property. They can not add additional constraints.

• Only valid matches can be used as a reference for a range, for this, the sh:class constraint of the target NodeShape is checked. If the target class of a NodeShape is schema:Hotel, but the property in question can not have that class as a valid range, then that NodeShape can not be referenced.

• It is possible to create circular Domain Specifications.