Common use cases for SHACL rules in RDF data modeling

Are you struggling with ensuring data quality or validating RDF data models? The Solution may be SHACL - Shapes Constraint Language. SHACL is born out of W3C, and it is a declarative language for defining constraints and shapes for RDF data models. SHACL creates an independent layer over RDF, which enables the user to add constraints and rules augmenting the data model's quality. In simpler terms, SHACL rules can help you ensure data conformity, completeness, and accuracy.

Do you wish to know how SHACL can be useful in real-life scenarios? In this article, we will explore common use cases of SHACL rules in RDF data modeling.

Ensuring terminology consistency

Suppose you have an RDF ontology representing medical procedures. It would be difficult for a clinician to understand your ontology if you use inconsistent terminologies like "operative," "procedure," and "surgery." In such a scenario, SHACL can be of great help. You can define rules that capture the consistency constraints of terminologies in your ontology. Let's have a look at an example.

ex: ProcedureShape a sh:NodeShape ;
                  sh:property
                  [
                      sh:path       ex:hasProcedureType ;
                      sh:datatype   xsd:string ;
                      sh:pattern    "surgery|operative|procedure"
                  ] .

This SHACL constraint ensures that the values for the property ex:hasProcedureType match the given pattern. In this case, the pattern is defined as a regular expression that matches exactly three terms - surgery, operative, and procedure.

Validating cardinality

The cardinality of a property is the number of values it can take for an RDF triple. SHACL rules can assist you in validating the cardinality of a property. Here is an example.

ex:Person a sh:NodeShape;
              sh:property [
                 sh:path ex:hasFather;
                 sh:maxCount 1;
              ] .
ex:hasFather a rdf:Property; 
              rdfs:domain ex:Person. 

The above SHACL specifies that every instance of ex:Person should have at most one father. It also defines that the ex:hasFather is a property for people, hence its domain is ex:Person.

Data completeness

Data quality frameworks require data to be complete to avoid incomplete data sets. Ensuring data completeness can be achieved through SHACL rules. Here is an example of a SHACL rule that validates that every Person has a name, age, and address.

ex:missingInfo a sh:NodeShape ;
                sh:property
                [
                    sh:path       ex:hasName;
                    sh:minCount        1
                ], [
                    sh:path       ex:hasAge;
                    sh:minCount        1
                ], [
                    sh:path       ex:hasAddress;
                    sh:minCount        1
                ].

ex:Person a sh:NodeShape ;
           sh:property
           [
               sh:path       ex:hasName;
               sh:datatype   xsd:string
           ], [
               sh:path       ex:hasAge;
               sh:datatype   xsd:integer
           ], [
               sh:path       ex:hasAddress;
               sh:datatype   xsd:string
           ], [
               sh:path       ex:hasFather;
               sh:class      ex:Person
           ].

If you have RDF data with a Person type, SHACL can validate whether the data includes all of the required properties (Name, age, address) for it to be considered complete. In case the particular RDF data doesn't follow the constraint, the specified rule in SHACL can detect the incompleteness of information, indicating that further information needs to be collected for that RDF data.

Chaining properties

SHACL enables you to apply a constraint across a chain of properties.

ex:DirectSiblingPropertyChain
    rdf:type sh:PropertyChain ;
    sh:property ex:hasSibling ;
                ex:hasMother ;
                ex:hasFather .
ex:PersonShape
    rdf:type sh:NodeShape ;
    sh:property
        [ sh:path  ex:hasSiblings ;
          sh:node ex:SiblingsShape ] .
          
ex:SiblingsShape
    rdf:type sh:NodeShape ;
    sh:property
        [ sh:path ( ex:hasMother ex:hasFather ex:hasSibling ) ;
          sh:minCount 2 ] .

In the example above, the DirectSiblingPropertyChain defines a chain of RDF properties that represent Sister/Brother relationships. The Person Shape is described with a specific property hasSiblings, it has a node property pointing to SiblingsShape. The SiblingsShape node shape applies a chained property of (hasMother, hasFather, hasSibling), and enforces the minCount of 2 siblings. This SHACL constraint ensures that every Person in the RDF data having at least two siblings.

Checking external vocabularies

SHACL rules are useful for ensuring the correctness of RDF data modeling and vocabularies. SHACL makes it possible to apply reference information(RDF vocabularies or ontology) into SHACL constraints. For instance, a user can use an external vocabulary schema.org to check whether their RDF data meets schema.org guidelines or ontology. Here's a simplified example that illustrates how to integrate SHACL rules with external ontologies.

PREFIX skosext: <http://www.skosext.org/skosext#>
ex:Place
    a sh:NodeShape ;
    sh:property
        [ sh:path ex:name ;
          sh:maxCount 1 ] ,
        [ sh:path skosext:spatialCoverage ;
          sh:node skos:Concept ;
          sh:property [ sh:path skos:prefLabel ] ] .

The above example applies SHACL rules using the SKOS(RDF Vocabularies) model, checking that every node of ex:Place has a name, and an example of the SKOS-specific constraint is spatialCoverage under skosext namespace should have a skos:prefLabel property. This capability is useful when using industry-related terminologies or external datasets like archives, museums or linked datasets for integrating into your own RDF data sets.

Conclusion

SHACL is a fascinating technology that serves as a validation tool for RDF semantic web data models. SHACL provides multiple advantages, such as ensuring data consistency and completeness, handling ontology imports, and even dealing with the creation of required relationships between objects. Furthermore, SHACL enables a rich set of rules, constraints and enables an ontology designer to create customized rules to suit their specific use cases. When used correctly, SHACL provides an excellent tool to validate and maintain RDF data models in complex and larger datasets.

We hope that this article has given you insights into how SHACL rules can be applied to real-world scenarios. The examples shown, i.e., terminologies consistency, specifying cardinality, ensuring data completeness, chaining properties, and checking external vocabularies, are a good starting point to apply SHACL and achieve high-quality RDF data models.

If you are interested in learning more about SHACL and its features, head over to shaclrules.com, which is an excellent source of knowledge, tutorials and projects related to SHACL.

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