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provide a language that is called Description Logic or DL for short. One of the key features of DL is that 
these superclass-subclass relationships (aka subsumption relationships) can be computed automatically by 
a reasoner – more on this later. Figure 3.3 shows a representation of some classes containing individuals – 
classes are represented as ovals, like sets in Venn diagrams. 
In OWL classes can be built up of descriptions that specify the conditions that must be satisﬁed by an 
individual for it to be a member of the class. How to formulate these descriptions will be explained as the 
tutorial progresses.