OWL vs. SHACL: A Practical Guide to Semantic Modeling and Data Validation

As semantic technologies become essential for data standardization and exchange, knowing what to put in OWL (Web Ontology Language) and SHACL (Shapes Constraint Language) is critical. Here’s a simple rule of thumb based on practices followed in the SEMIC context:

Rule of Thumb:

In practice, we follow this approach (especially in SEMIC):

• OWL: Use for lightweight vocabulary declaration.
• SHACL: Use for defining instantiation constraints and ensuring data consistency (e.g., domain, range, cardinality, controlled lists).

Why?
OWL defines what exists in your domain (classes, properties).
SHACL defines how it should be used in data (rules, constraints, validation).

OWL: Lightweight Ontology for Vocabulary Declaration

In OWL, define the vocabulary that represents your domain. This includes the basic constructs needed for describing classes and object properties.

• Declare Classes & Properties: Use owl:Class, owl:ObjectProperty, and owl:DatatypeProperty for domain concepts and relationships.
• Avoid Complexity: Keep the ontology simple and focused to maximize reusability.
• Add Clear Labels & Definitions: Use rdfs:label and skos:definition annotations to provide clarity and meaning to your concepts.

Inventory of OWL Statement Types:

• Classes: owl:Class for domain entities.
• Object Properties: owl:ObjectProperty for relationships between entities.
• Datatype Properties: owl:DatatypeProperty for linking classes to literal values.
• Restrictions: Use owl:Restriction to define constraints on properties (e.g.,minCardinality, maxCardinality).

For a more precise list of statements and modelling convention, check the SEMIC style guide.

SHACL: Data Validation and Constraints

SHACL helps ensure that the data follows the rules and constraints defined in the ontology.

• Domains & Ranges: Ensure that properties are used within their defined domains and ranges.
• Define Cardinality: Specify the minimum and maximum occurrences of properties.
• Control Data Values: Use controlled lists to validate data values and enforce patterns.

SHACL Statement Types:

In SHACL, the most common statement types for enforcing data validation include:

• Node Shapes: Define constraints on the nodes of a graph (e.g., sh:NodeShape, sh:PropertyShape).
• Property Shapes: Define constraints on the properties of nodes (e.g., sh:property).
• Data Types and Literals: Validate that data conforms to specific types or formats.

Example: The eProcurement Ontology (ePO)

The eProcurement Ontology (ePO) defines the concepts and constraints related to EU public procurement. You can explore the ontology and the related SHACL shapes in the ePO GitHub repository.

Key Takeaway

• Use OWL for the vocabulary (concepts and relationships).
• Use SHACL for enforcing data constraints (cardinality, domains, ranges, controlled lists).

Together, they help create a clear, reusable, and validated semantic model.

Let’s Discuss

How do you balance OWL and SHACL in your projects? Share your tips or practices.

Contributed by Meaningfier Jana Ahmad.

___

Meaningfy continues to support the European Commission’s initiatives, leading the charge toward a transparent, efficient, and interconnected European public sector. If you represent a European Institution or a public company that needs to implement an interoperability solution, visit this page or contact us for tailored support and effective implementation.