In CSS, it is possible to have containers where all its resources conform to a given SHACL shape. Providing shape validation ensures that applications can then rely on the fact that the structure of the graph in the resources is valid.
A container can be made shape constrained by editing its description resource.
A triple of the form ?container ldp:constrainedBy ?shape . must be added,
where ?container is the URL of the container being made constrained and ?shape is the URL of the SHACL shape.
A precondition for making a container constrained is that the container must not contain any resources. Furthermore, it is only possible to initialise one shape resource per container.
Exposing that a container is constrained by shape is done through advertising a Link Header
with "rel" http://www.w3.org/ns/ldp#constrainedBy as is defined in LDP 4.2.1.6.
Only resources can be created that conform to the constraints of a constrained container. However, some additional restrictions are enforced by the server on that container:
- It is not possible to add any non-RDF resources.
- Creating containers within this constrained container is not allowed.
- Requests that result in a resource where no
sh:targetClassesfrom the shape are present are prohibited and will thus produce an error.
In this example, we want to constrain a container http://localhost:3000/container/ with a SHACL shape.
We have started the CSS with the default configuration and have already created a container at http://localhost:3000/container/
and added a SHACL shape at http://localhost:3000/shape.
We make the container constrained by adding the constraint to the description resource of the container.
curl -X PATCH 'http://localhost:3000/container/.meta' \
-H 'Content-Type: text/n3' \
--data-raw '@prefix solid: <http://www.w3.org/ns/solid/terms#>.
<> a solid:InsertDeletePatch;
solid:inserts { <http://localhost:3000/container/> <http://www.w3.org/ns/ldp#constrainedBy> <http://localhost:3000/shape>. }.'After this update, we can verify that the container is indeed constrained with a shape by
performing a HEAD request to the container.
curl --head http://localhost:3000/container/
which will produce a response with at least this header:
Link: <http://localhost:3000/shape>; rel="http://www.w3.org/ns/ldp#constrainedBy"The container is now indeed constrained by the shape. This means that all the resources that will be added to this container conform to the shape.
In this example, we used a SHACL shape that was stored on the server. However, we can use any SHACL shape that can be fetched on the web via HTTP.