A definition of a set of context variables to be considered is received, wherein the context variables represent categories of situations in which the computer system can be. A definition of a set of activities to be considered is also received, wherein the activities represent activities that can be performed using the computer system. For each context variable to be considered, a definition of a set of states to be considered is received, wherein the states represent situations in which the computer system can be. For each context variable to be considered, a specification of first probability distributions for each corresponding state is received. For each context variable to be considered, for each activity to be considered, a specification of second probability distributions to represent the likelihood of the activity being performed in the corresponding context is received. Usage data is generated using the first second probability distributions.