One proposed way to realize the AmI vision is to turn everyday objects into artifacts (by adding sensing, computation and communication abilities) and then use them as components of Ubiquitous Computing (UbiComp) applications within an Ami environment. The (re)configuration of associations among these artifacts will enable people to set up their living spaces in a way that will serve them best minimizing at the same time the required human intervention. During the development and deployment of UbiComp applications, a number of key issues arise such as semantic interoperability and service discovery. The target of this paper is to show how ontologies can be used into UbiComp systems so that to address such issues. We support our approach by presenting the ontology that we developed and integrated into a framework that supports the composition of UbiComp applications.