I don’t know whether you said that a CEP application must necessarily have a model. It may have, or it may not. A rule-based approach (in its general acceptation) is not considered as a model. In the AI terminology, rules are considered as “shallow knowledge”, while models are considered as “deep knowledge”. Shallow knowledge expresses the people’s experience, links symptoms to causes directly, while deep knowledge establishes the links using a model, and the model can be interpreted. Shallow knowledge is very helpful in many cases, and as deep knowledge it also allows detecting situations. Of course, the cooperation of both is desirable to build more powerful systems. I did a rapid search, and below are 3 entries for reference: