text: 4.10.1 Property restrictions 
  In OWL properties define binary relations with the same semantics and characteristics as binary relations 
  in First Order Logic. There are two types of OWL properties for describing a domain: Object properties 
  and Data properties. Object properties have classes as their domain and range. Data properties have 
  classes as their domain and simple datatypes such as xsd:string or xsd:dateTime as their range. In 
  figure 3.3 the individual Michael is related to the individual USA by the property livesIn. Consider all 
  the individuals who are an instance of Person and also have the same relation, that each livesIn the 
  USA. This group is a set or OWL class such as USAResidents. In OWL a class can be defined by 
  describing the various properties and values that hold for all individuals in the class. Such definitions are 
  called*restrictions*in OWL. 