Validating interactive system design through the verification of formal task and system models

This paper addresses the problem of the articulation between task modelling and system modelling in the design of interactive software. We aim at providing solutions allowing the software designers to use efficiently task models during the design process, and to check that the software being built actually corresponds to the requirements elicited during the task analysis phase. The proposed approach is twofold : Firstly, we use the User Action Notation, a semi-formal task modelling formalism, and we present a translation scheme allowing to transform the User Action Notation constructs into Petri nets. Secondly, we use the Interactive Cooperative Objects formalism (based on Petri nets and on the object-oriented approach) to build the model of the system. We finally use the mathematical analysis techniques stemming from the Petri net theory to analyse and validate the cooperation between task models and system model. The approach is presented through a case study, showing the User Action Notation task models, the equivalent Petri net models and the Interactive Cooperative Object system model.