i just think that these evaluation techniques are sufficient for good results because we know that the heuristics are specific guidelines and they are different for every S/W product. questionnaires are very good tools from the user's feed back perceptive as we can get users opinions in an objective form, cognition is again very very useful tool for evaluation of the product because in this technique the experts behave as they are the real end users of the product and identify the problems and issues that a user can/will face to fulfill its goal. overall a good product must fulfill the usability goals and i think from these evaluation techniques we can achieve these goals. must listen the related lecture and students are requested to comment on it and discuss if i am right or not