A Bigtable is a sparse, distributed, persistent multidimensional sorted map.
The map is indexed by a row key, column key, and a timestamp; each value in the map is an uninterpreted array of bytes.
HBase uses a data model very similar to that of Bigtable. Users store data rows in labelled tables. A data row has a sortable key and an arbitrary number of columns. The table is stored sparsely, so that rows in the same table can have crazily-varying columns, if the user likes.