29 September 2026 11:52
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Define classes, attach SPIN constructors that drive create forms, and add constraints that validate instances

To manage instances, you first need classes that represent them in your dataspace's model. Not only will they serve as RDF types of the instances, but they will also have constructors attached that define the default properties and their (data)types for that class.

The model is managed in the administration dataspace of a dataspace. Head there by clicking the in the navigation bar and then choosing Administration.

In order to manage the access control, or the model of a dataspace, the agent needs to be a member of the owners group.

This guide uses the Northwind Traders model and its schema:Product class as the example — the demo app ships exactly this constructor and constraint in its namespace ontology, so the finished result can be compared against admin/model/ns.ttl.

Create a constructor

Use the following SPARQL CONSTRUCT query as a constructor for the Product class. The typed blank nodes tell the form which control to render: a string input for the name and identifier, resource typeaheads for the category and supplier.

PREFIX schema: <https://schema.org/>
PREFIX xsd:    <http://www.w3.org/2001/XMLSchema#>

CONSTRUCT
{
  $this schema:name [ a xsd:string ] ;
    schema:identifier [ a xsd:string ] ;
    schema:category [ a schema:ProductGroup ] ;
    schema:provider [ a schema:Corporation ] .
}
WHERE {}

In the administration dataspace, follow these steps:

  1. Click the Create dropdown at the bottom of the page
  2. Click on CONSTRUCT in the dropdown list that appears
  3. Switch the Blank node dropdown to URI and enter https://localhost:4443/ns#ProductConstructor
  4. Fill out the mandatory fields in the form:
    Label
    Enter Product constructor
    IsDefinedBy
    Select Namespace from the list — the dataspace’s namespace ontology, in which the query is defined
    Text
    Enter the SPARQL CONSTRUCT query string
  5. Click Save

Follow the same steps for Category (schema:ProductGroup) if you want its instances to be creatable too.

Read more about constructors.

Create a constraint

To control data quality, you may want to make some of the instance properties mandatory. For example, a schema:Product instance should always have a schema:name value.

In the administration dataspace, follow these steps:

  1. Click the Create dropdown at the bottom of the page
  2. Click on Missing property value in the dropdown list that appears
  3. Fill out the fields in the form:
    Label
    Enter Missing schema:name
    IsDefinedBy
    Type Namespace into the input (which provides autocomplete)
    Select Namespace from the list — the dataspace’s namespace ontology, in which the query is defined
    Arg1
    Enter https://schema.org/name
  4. Click Save

Read more about constraints.

Create classes

In the administration dataspace, follow these steps to create the product class:

  1. Click the Create dropdown at the bottom of the page
  2. Click on Class in the dropdown list that appears
  3. Switch the Blank node dropdown to URI and enter https://schema.org/Product — reusing the schema.org term rather than minting your own
  4. Fill out the mandatory fields in the form:
    Label
    Enter Product
    IsDefinedBy
    Select Namespace from the list — the dataspace’s namespace ontology, in which the class is defined
    Constructor
    Type Product constructor into the input (which provides autocomplete)
    Select Product constructor from the list — this is the query you created beforehand
  5. Click Save

Read more about classes.

What ended up in the model

The three steps added the following description to the namespace ontology document — the same wiring the demo app ships:

schema:Product spin:constructor <https://localhost:4443/ns#ProductConstructor> ;
    spin:constraint <https://localhost:4443/ns#MissingName> ;
    rdfs:label "Product" .

<https://localhost:4443/ns#ProductConstructor> a ldh:Constructor ;
    rdfs:label "Product constructor" ;
    sp:text "CONSTRUCT { $this schema:name [ a xsd:string ] ; … } WHERE {}" .

<https://localhost:4443/ns#MissingName> a ldh:MissingPropertyValue ;
    rdfs:label "Missing schema:name" ;
    sp:arg1 schema:name .

From now on, Product can be chosen as the Type of a new Instance created from the Create dropdown of the end-user dataspace, and its form is then generated from the constructor, offering title, name, identifier, description, category, supplier and offer controls. A submission without a name is rejected with 422 Unprocessable Entity, carrying the constraint violation.

The generated Product create form, with the Missing schema:name violation shown after an empty submit