The Web Ontology Language (OWL) is a standard for defining the meaning of data in RDF knowledge graphs. While RDF tells you what the data is (triples), OWL tells you what it means — the rules, constraints, and relationships that govern your domain.
Think of OWL as the schema language for the Semantic Web. Just like a relational database has table definitions with foreign keys and constraints, OWL lets you define classes, properties, and logical axioms that describe your data's structure.
OWL constructs enable three powerful capabilities:
Automated Inference — Reasoners can derive new facts from existing data. If you say "every Employee is a Person" and "Nancy is an Employee", a reasoner automatically infers "Nancy is a Person."
Consistency Checking — Detect logical contradictions in your data. If you say "Products and People are disjoint" (nothing can be both), and some data says "Chai is both a Product and a Person," the reasoner flags the error.
Data Integration — When combining datasets from different sources, OWL axioms help align and merge data by making implicit relationships explicit.
Not all OWL features work the same way in every triplestore. OWL defines several profiles (subsets):
The Northwind ontology uses constructs that work across all profiles, with a few important distinctions:
subClassOf
equivalentClass
disjointWith
inverseOf
FunctionalProperty
propertyChainAxiom
allValuesFrom
someValuesFrom
AsymmetricProperty
IrreflexiveProperty
hasKey
This guide is organized into sections that mirror what you see in the RDF Studio Ontology Editor:
Each section includes real examples from the Northwind ontology — the same data you're exploring in RDF Studio right now.
Tip: Open the MODEL > Ontologies tab alongside this guide. Click on any class mentioned here to see its full definition in the editor.