In order to design interactive applications, the first step is usually the definition of user needs. While performing this step, activities may be modeled using task models. Some task model components express scheduling information that describes the task dynamics. According to a model-based approach, the dynamics of applications (i.e.: the dialog) can be formalized using a dialog model. Several approaches seek to exploit the task model information to perform the dialog model. This paper aims to show that the use of the hierarchical dialog model facilitates its design according to task model information during the whole iterative design process.