We are interested in understanding and simulating how humans elaborate plans in situations where knowledge is incomplete and how they interact to obtain missing information. Our human interaction model is based on the speech act theory to model the utterances and it uses timed automata to describe the dynamics of the dialogs. Our human planning model is implemented as a hierarchical blackboard architecture which manages opportunistic planning. The system BDIggy we propose, is a concurrent

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... entation of the planning model and the interaction model through the BDI concept. This system is used to simulate the human processes during cooperative problem solving.