George Lagogiannis Nikos A. Lorentzos Spyros Sioutas Theodoridis Evaggelos A Time Efficient Indexing Scheme for Complex Spatiotemporal Retrieval http://arxiv.org/abs/0805.1487 2008 CoRR abs/0805.1487 db/journals/corr/corr0805.html#abs-0805-1487 informal publication