Regarding the complexity of actual software systems, including web portals, it is becoming more and more difficult to develop software systems such that their real usage will satisfy their intended usage. To tackle this problem, we can compare the a priori assumptions about how the system should be used with the actual user behavior in order to decide how the system could be improved. For this aim, we propose to employ the same formalism to express the intended usage, the web portal model and the real usage extracted from system usage traces by data mining algorithms. Inspired from BioCham, we propose to use temporal logic and Kripke structure as such a common formalism.