In this talk we will review different approaches used for the generation, publication and acesss to ontology-based data streams coming from sensor networks. We will briefly describe the work done on the characterisation of sensor-based data sources and observations in the context of the W3C Semantic Sensor Network Incubator Group, which has resulted in an ontology for describing sensor networks. We will also analyse different alternatives that can be used for the generation of sensor data in RDF, including the identification of sensors and the transformation into the Sensor Network Ontology model. We will finally describe how sensor data sources can be accessed by means of SPARQL-STR queries, and the query rewriting methods used in the query execution process.