The proposed AgLOTOS formal specification language is dedicated to express BDI agent plans, according to the features and requirements of Ambient Intelligence (AmI). It offers a rich modular approach to express and compose elementary plans in order to execute them concurrently. We show how a plan is built automatically as a system of concurrent processes from the mental attitudes of the agent. In contrast to existing approaches, the plan is viewed as the realization of a whole set of partially ordered intentions. The AgLOTOS semantics accords with the possibility of updating some sub-plans on the fly, as the intention set of the BDI agent is revised.