Abstract. We study the extension of context ontologies towards enhanced qualitative spatio-temporal representations and reasoning. Our goal is to model and extract events that are important to the user from her context log, i.e. the history of context data collected over a longer period. We present a case study based on actual context ontologies and context data from the ContextWatcher mobile application. The presented work has been fully implemented in the DL-based reasoning engine RACERPRO.