Mixed Interactive Systems (MIS) is a generic term encompassing mixed and augmented reality, augmented virtuality, and tangible interfaces systems. The work we present in this paper deals with the design of such systems. Several models have been proposed to describe mixed interactive systems. However, these models neither integrate MIS in the global user activity, nor take into account the dynamics of mixed interactive situations. Task models offer an interesting approach to cover these aspects. The purpose of our work is to contribute to the design of MIS by articulating mixed interaction models and tasks models. This paper presents complementarities and common points between these models, which will be used as the basis for the rules to articulate the task and interaction models.