This ontology describes sensors, observations, and related concepts. It also describes events and their correlations. The final aim is to support a better description of sensor context. This ontology is developed by DERI (http://www.deri.ie) for the SPITFIRE project (http://spitfire-project.eu). It is based on the alignment among the W3C Semantic Sensor Networks Incubator Group (SSN-XG) ontology, the Dolce-DnS Ultralite ontology and the Event Model F ontology.