code: public double getAttributeNumber(ScoreAttribute sa) {
  		if (!(sa.getDefaultValue() instanceof Number))
  			throw new RuntimeException(sa.toString()
  					+ " is not a number attribute");
  		return ((Number) getAttributeObject(sa)).doubleValue();
  	}
docs: Returns the number value associated to an attribute, as
  a double.
  
  @throws RuntimeException if sa doesn't accept boolean value