text: 1. Class expressions. This is the name of a class followed by parentheses with a parameter inside. 
  For example Customer(?c) will bind ?c to an instance of the class Customer and (assuming the 
  rest of the antecedent is satisfied) will iterate over each instance of the Customer class. 
  
  2. Property expressions. This is the name of a property followed by parentheses and two parameters: 
  
  the first for the individual that is being tested and the second to bind to the value of that property 
  for that individual. Note that since individuals can have more than one value for a property this 
  can also create iteration, where the rules will iterate over every property value for each individual. 
  E.g., purchasedPizza(?c, ?p) will bind ?p to each Pizza purchased by each customer 
  ?c. 
  
  3. Built-in functions. SWRL has a number of built-in functions for doing mathematical tests, string 
  tests, etc. The SWRL built-ins are documented here: https://www.w3.org/Submission/SWRL/ 
  All SWRL built-ins are prefaced by the swrlb prefix. E.g., the math built-in 
  swrlb:greaterThan(?np, 1) succeeds if the value of ?np is greater than 1. 