1. A method for searching objects in a database by means of an index data structure which associates object attribute values to collections of spatial elements—for example tiles of a quadtree or cuboids of an octtree—defined to partition a space, especially a two-dimensional plane or a three-dimensional space, herein a predefined number of spatial elements being combinable to a next-level spatial element, the method comprising: searching the index data structure for a first input search pattern and, if the first input search pattern is associated to a first collection of spatial elements through the index data structure, including all spatial elements from the first collection into a first candidate set of spatial elements, wherein, if the number of spatial elements in the first candidate set exceeds a certain limit, some or all of the spatial elements are combined to a reduced number of next-level spatial elements; searching the index data structure for a second input search pattern and, if the second input search pattern is associated to a second collection of spatial elements through the index data structure, including all spatial elements from the second collection into a second candidate set of spatial elements, wherein, if the number of spatial elements in the second candidate set exceeds a certain limit, some or all of the spatial elements are combined to a reduced number of next-level spatial elements; forming, from the first candidate set and the second candidate set, a combined candidate set of spatial elements; searching, in the combined candidate set of spatial elements, for objects that match the first input search pattern and the input second search pattern to obtain a set of result objects wherein in the combined candidate set formed from the first candidate set and the second candidate set some or all of the spatial elements are combined to a reduced number of next-level spatial elements if the number of spatial elements in the combined candidate set exceeds a predefined threshold value.
1. A method for searching objects in a database by means of an index data structure which associates object attribute values to collections of spatial elements—for example tiles of a quadtree or cuboids of an octtree—defined to partition a space, especially a two-dimensional plane or a three-dimensional space, herein a predefined number of spatial elements being combinable to a next-level spatial element, the method comprising: searching the index data structure for a first input search pattern and, if the first input search pattern is associated to a first collection of spatial elements through the index data structure, including all spatial elements from the first collection into a first candidate set of spatial elements, wherein, if the number of spatial elements in the first candidate set exceeds a certain limit, some or all of the spatial elements are combined to a reduced number of next-level spatial elements; searching the index data structure for a second input search pattern and, if the second input search pattern is associated to a second collection of spatial elements through the index data structure, including all spatial elements from the second collection into a second candidate set of spatial elements, wherein, if the number of spatial elements in the second candidate set exceeds a certain limit, some or all of the spatial elements are combined to a reduced number of next-level spatial elements; forming, from the first candidate set and the second candidate set, a combined candidate set of spatial elements; searching, in the combined candidate set of spatial elements, for objects that match the first input search pattern and the input second search pattern to obtain a set of result objects wherein in the combined candidate set formed from the first candidate set and the second candidate set some or all of the spatial elements are combined to a reduced number of next-level spatial elements if the number of spatial elements in the combined candidate set exceeds a predefined threshold value. 21. The method according to claim 1 , wherein the first and second search pattern are input through a medium such as a voice input device yielding a multitude of search query variants each consisting of several input search patterns instead of a single search query, and wherein the estimated cardinality of candidate sets computed for search patterns from the search query variants through a lookup in an index data structure or the cardinality of combined candidate sets computed for search query variants is used to guide the selection of a subset of search query variants for further processing or to guide the assignment of priorities to the individual search query variants influencing the order of their further processing.