The need to improve communication between humans and computers has been instrumental in de ning new modalities of communication, and new ways of interacting with machines. Gestures can convey information for which other modalities are not e cient or suitable. In natural and user-friendly interaction, gesturescanbeused, asasinglemodality, orcombinedinmultimodalinteraction schemes which involvespeech, or textual media. Speci cation methodologiescan be developed to design advanced interaction processes in order to de ne what kind of gestures are used, which meaning they convey, and what the...