Due to the propagation of personal computers, it is increasingly important to build highly usable user interfaces, taking into account users characteristics, preferences, and needs. Diverse models have been proposed to cope with the complexity of human-computer interaction (HCI) design. However, most of them deal at once with elements that should be addressed by distinct models. Moreover, many of these models are based on cognitive theories, which focus mainly on the individual interacting with an application, without exploring the fact that an application is the product of a rational decision-making process carried out by a designer. This gap is dealt with by Semiotic Engineering, a theory of HCI which views the interface as a designer-to-users message, representing the designers solution to what he believes are the users problems, needs, and preferences. In this message, he is telling users, directly or indirectly, what he had in mind when he conceived the application. Within Semiotic Engineering, this work extends scenarios, adapts an existing task model and builds a model which treats interaction as conversation. Our goal is to conceive models and representations that serve, each under a clear perspective, as epistemic tools that support the designers reflection about the interactive solution being conceived. A small case study was conducted to evaluate the quality of an interactive solution designed using the proposed task and interaction models, in comparison with CTT, a widely used task model.