Panayotis Partsinevelos Nectaria Tryfona Handling High-Level Queries in Location-Based Services for User Groups. 213-234 2006 10 GeoInformatica 2 http://dx.doi.org/10.1007/s10707-006-7580-7 db/journals/geoinformatica/geoinformatica10.html#PartsinevelosT06