code: @Override
  	public String getKey(Object wrapped)
  	{
  		if (wrapped instanceof BioPAXElement)
  		{
  			return ((BioPAXElement) wrapped).getUri();
  		}
  
  		throw new IllegalArgumentException("Object cannot be wrapped: " + wrapped);
  	}
docs: RDF IDs of elements is used as key in the object map.
  @param wrapped Object to wrap
  @return Key