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 settings in the navigation bar and then choosing Administration.

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In order to manage the access control, or the model of a dataspace,\n 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\n exactly this constructor and constraint in its namespace ontology, so the finished result can be compared against\n 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/>\nPREFIX xsd:    <http://www.w3.org/2001/XMLSchema#>\n\nCONSTRUCT\n{\n  $this schema:name [ a xsd:string ] ;\n    schema:identifier [ a xsd:string ] ;\n    schema:category [ a schema:ProductGroup ] ;\n    schema:provider [ a schema:Corporation ] .\n}\nWHERE {}

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In the administration dataspace, follow these steps:

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

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

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.

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In the administration dataspace, follow these steps:

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

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Create classes

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

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

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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> ;\n    spin:constraint <https://localhost:4443/ns#MissingName> ;\n    rdfs:label \"Product\" .\n\n<https://localhost:4443/ns#ProductConstructor> a ldh:Constructor ;\n    rdfs:label \"Product constructor\" ;\n    sp:text \"CONSTRUCT { $this schema:name [ a xsd:string ] ; … } WHERE {}\" .\n\n<https://localhost:4443/ns#MissingName> a ldh:MissingPropertyValue ;\n    rdfs:label \"Missing schema:name\" ;\n    sp:arg1 schema:name .

From now on, Product can be chosen as the Type of a new Instance created from the Create expand_more dropdown of the\n 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\n 422 Unprocessable Entity, carrying the constraint violation.

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