A subproperty is a property that is a specialization of another property (its superproperty). Specialization or IsA relationship means that:
1. all instances of the subproperty are also instances of its superproperty,
2. the intension of the subproperty extends the intension of the superproperty, i.e. its traits are more restrictive than that of its superproperty,
3. the domain of the subproperty is the same as the domain of its superproperty or a subclass of that domain,
4. the range of the subproperty is the same as the range of its superproperty or a subclass of that range,
5. the subproperty inherits the definition of all of the properties declared for its superproperty without exceptions (strict inheritance), in addition to having none, one or more properties of its own.

A subproperty can have more than one immediate superproperty and consequently inherits the properties of all of its superproperties (multiple inheritance). The IsA relationship or specialization between two or more properties gives rise to the structure we call a property hierarchy. The IsA relationship is transitive and may not be cyclic.
Some object-oriented programming languages, such as C++, do not contain constructs that allow for the expression of the specialization of properties as sub-properties.
Alternatively, a property may be subproperty of the inverse of another property, i.e. reading the property from range to domain. In that case,
1. all instances of the subproperty are also instances of the inverse of the other property,
2. the intension of the subproperty extends the intension of the inverse of the other property, i.e. its traits are more restrictive than that of the inverse of the other property,
3. the domain of the subproperty is the same as the range of the other property or a subclass of that range,
4. the range of the subproperty is the same as the domain of the other property or a subclass of that domain,
5. the subproperty inherits the definition of all of the properties declared for the other property without exceptions (strict inheritance), in addition to having none, one or more properties of its own. The definitions of inherited properties have to be interpreted in the inverse sense of direction of the subproperty, i.e., from range to domain.