Recently, evaluating the usability of mobile applications is gaining a lot of attention. The interest is focused on the user interface design choices that may lead to the rejection of the application. The evaluation is usually performed at the last stage of the development life cycle when the system is fully implemented. At this stage, it is difficult/expensive to go back to the design and make the required changes to solve usability issues. This problem may be alleviated by using the

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... en Engineering (MDE) approach, where conceptual models (elaborated at the design phase) undergo a series of transformations to generate the final applications, as automatically as possible. The transformation process establishes a mechanism of traceability between these conceptual models and the final application. Due to this mechanism, the analysis of these models to improve their usability is likely to preserve this usability at the final application or improve it. The present paper presents a model-based approach to evaluate the usability of mobile applications in the design phase. The proposed approach provides a set of usability metrics that are defined based on conceptual primitives that constitute the conceptual models. The objective is to allow the measurement of usability issues from the conceptual models. Prior validation of our proposal is presented in this paper.