Inference in ontologies

 

Why inference changes what you can retrieve from an ontology

One of the most interesting aspects of ontologies is that the same query can produce different results depending on whether reasoning has been applied or not.

Without inference, a query only retrieves what is explicitly asserted.

With inference, the ontology can reveal knowledge that was never directly written — but logically follows from the axioms.

Example

Suppose we define:

• SevereDengue ⊑ DengueCase

• Patient123 rdf:type SevereDengue

Now consider the query:

SELECT ?x
WHERE {
  ?x a :DengueCase .
}

Without inference

Result:

• no result (if Patient123 was only declared as SevereDengue)

With inference enabled

Result:

• Patient123

Why?

Because the reasoner derives:

Patient123 rdf:type DengueCase .

even though this triple was never explicitly stored.

This means:

Inference transforms ontologies from static structures into knowledge generators.

The query remains the same.

The ontology becomes richer because logic adds new answers.

In practice:

Without reasoning → retrieve asserted facts
With reasoning → retrieve asserted + inferred facts

That is one of the key differences between querying data and querying semantic knowledge.

Examples in this post were developed with AI support.

#SemanticWeb #Ontology #OWL #SPARQL #Inference #Reasoning  #Metadata #SemanticIntegration