In the last years, researchers are devoting many efforts to improve technological aspects of the Internet of Things (IoT), while little attention has dedicated to social and practical sides. Professional developers program the behavior of smart objects. In addition, often the functionality exposed by a single object are not able, alone, to exhaustively support the end users' tasks. The opportunities offered by IoT can be amplified if new highlevel abstractions and interaction paradigms enable also non-technical users to compose the behavior of multiple objects. To fulfill this goal, we present a model to express rules for smart object composition, which includes new operators for defining rules coupling multiple events and conditions exposed by smart objects, and for defining temporal and spatial constraints on rule activation. Such model has been implemented in a Web application whose composition paradigm has been designed during an elicitation study with 25 participants
