A system and method for modeling and evaluating resource requirements of services is disclosed. The system and method in one aspect enable describing an application session in a software model, for example, as a sequence of events in a sequence diagram, annotating the sequence diagram with information and using the sequence diagram and the information to create a mathematical model such as a Markov model that represents the application session. Once in Markov form the service can be analyzed. The system may include a user interface for allowing a user to enter annotations to the sequence diagram.