text: 4.6 OWL Properties 
  OWL Properties represent relationships. There are three types of properties, Object properties, Data 
  properties and Annotation properties. Object properties are relationships between two individuals. Data 
  properties are relations between an individual and a datatype such as xsd:string or xsd:dateTime. 
  Annotation properties also usually have datatypes as values although they can have objects. An 
  annotation property is usually meta-data such as a comment or a label. In OWL only individuals can have 
  values for object and data properties, but any entity can have an annotation property value since meta-data 
  applies to all entities. Annotation properties usually can’t be reasoned about. For example, SWRL rules 
  which we will cover later cannot view or change the value of annotation properties. In this chapter we 
  will focus on Object properties. Data properties are described in Chapter 5. In the current version of the 
  tutorial we are only discussing the annotation property rdfs:label (see chapter 7) however they are 
  fairly intuitive. 
  
  Properties may be created using the Object Properties sub-tab of the Entities tab shown in figure 4.11. 
  Just as all OWL classes ultimately are a subclass of owl:Thing, all properties are ultimately a sub- 
  property of owl:topObjectProperty. A sub-property is similar to a subclass except it is about the 
  tuples in a property. For example, hasFather would be a sub-property of hasParent because all the 
  tuples in hasFather are in hasParent but not vice versa. E.g., if Sasha hasFather Barack then she 
  also hasParent Barack. However, she also hasParent Michelle but it is not the case that she 
  hasFather Michelle. Rather she hasMother Michelle, i.e., hasMother is also a sub-property of 
  hasParent. 