1. A computer-implemented process to summarize data, comprising: creating a trie-structure to index the data wherein: each node of the trie-structure represents a particular region of a domain of the data, a root node represents the whole domain of data to be indexed, each parent node fully contains the regions of its children in the trie-structure, and leaves of the trie-structure contain occupied bits indicating whether tuples in the set of data exist in the particular region of data.