In our previous works, we issued a significant difference between active Web services, that help carry out an action - e.g. buying a ticket to next Saturday?s representation in the theater - and informative Web services that merely search for information - e.g. querying some databases to get a list of available CD?s. This paper presents a dynamic logic for modeling accurately this distinction among composite Web services. We use a logical formalism allowing a calculus on complex Web services preconditions and effects. On the one hand, this formalism enlightens that activeWeb services modeling does not fall back to database update, when resources are taken into account (e.g. the number of seats in the theater). On the other hand, it models active Web service as a composed one : an informative Web service gathers information, a choice function is applied and feeds the input of an updating Web service.