Writing SHACL shapes

This session is about expressing syntactic constraints on RDF graph using the Shapes Constraint Language SHACL.

Objectives

• Understand existing shape schemas.
• Define constraints on what graph shapes are expected in the case of product data.
• Validate your shapes against RDF data.

Existing shapes for schema.org

TopQuadrant, a software company specialised in Semantic Web data management, provides a shape schema that expresses some of the constraints described informally in Schema.org specifications.

Answer the following questions in the email you send at the end of the session to Antoine Zimmermann and Victor Charpenay.

• When was this version of the SHACL schema of schema.org edited?
• Find where the schema:Order class is defined. What is the datatype for the value of the rdfs:comment for schema:Order?
• You should see that there are lots of values for sh:property. Consider schema:Order-orderDate. Find its definition in the file. What is the type of this entity?
• There is a constraint defined for schema:Order-orderDate as an sh:or constraint. Assuming ex:order is an instance of schema:Order, to which kind of entities does this constraint apply?. What is the constraint about? Guess what the constraint is telling by providing a correct example and an incorrect example. Write your answer in the email to us.
• Using the SHACL playground, you can test if an RDF graph validates a SHACL document. The box on the top left is where you enter the shape document. You can copy-paste the document from TopQuadrant. The box on the top right is where you put the RDF graph for the things of interest. For example, describe the order ex:order using schema.org, assming it has been placed today on LDLC for a Seagate BarraCuda hard disk drive at the price indicated in the offer. Include a description of the product and the offer as well (hint: the product and the offer are already described in JSON-LD in the web page). Refer to the documentation for schema:Order to describe the order. Then validate your entire graph against the SHACL schema. Copy the input RDF graph and the validation report to your email to us (both graphs should be in Turtle).

Write your own shape constraints

DBpedia generates RDF triples from Wikipedia infoboxes. On Wikipedia, infoboxes are in fact templates documented in special pages in the wiki. One such template is Infobox university. You will write SHACL shapes that capture the constraints of this template and validate DBpedia entities against these shapes.

For this part, write all your answers in a Turtle file with only SHACL shapes. No DBpedia statements should be included.

• First read general documentation about infoboxes on Wikipedia, then read the documentation of the Infobox university template. Compare with an instance of university on DBpedia, e.g. Arizona State University. How are template parameters turned into RDF properties? In future questions, make sure you map template parameters to existing properties under the dbp: namespace in your SHACL shapes.
• Write a shape for universities specifying that they have a name, a logo, a number of students, a president, that they are located in a city and that they were established a certain year. What node type do you choose for each of these properties?
• As per the documentation, the number of students can be expressed with the parameter students or, equivalently, the parameter enrollment. Use sh:or in your shape to express this alternative.
• Some of the properties, such as motto and image_alt, are optional but must be unique. How can you express that constraint?
• The geo-coordinates associated with a university must themselves be provided via a template (Coord). Write another shape for geo-coordinates as per this new template and link to it in the university shape (with sh:node).
• Many Wikipedia pages use the university template. The full list is here. Choose several examples of universities on Wikipedia, find their counterpart in DBpedia and use the RDF playground to validate DBpedia statements about these universities, as per your shapes.