# Data Property Axioms

Data properties link individuals to data values.

A set of instances connected to the property is called a property extension.

## Contents

## SubDataPropertyOf axiom

This axiom says that a property 'p1' is a subproperty 'sp1' of another property 'p2'. It also means that the instances of the subproperty are subsets to the property extension of the second property.

## Equivalent data properties axiom

Equivalent property axioms exist when two properties have the same property extension.

## Disjoint data properties axiom

Two properties are disjoint when they don't have individuals in common.

## Functional data property axiom

A functional property is a property which can only have one value.

For an individual 'x', there can be only one definite individual 'y' such that 'x' is connected by the data property expression 'DPE' to 'y'.

For example: FunctionalDataProperty( a:hasAge ) Each object can have at most one age. DataPropertyAssertion( a:hasAge a:John "21"^^xsd:integer ) John is twenty-one years old.

## Data property domain axiom

This axiom states that the class expression is the domain of the data property expression.

## Data Property range axiom

It says that the data range is the range of the data property expression.