US Patent 7567973 Storing a sparse table using locality groups

Each of a plurality of data items is stored in a table data structure. The table structure includes a plurality of columns. Each of the columns is associated with one of a plurality of locality groups. Each locality group is stored as one or more corresponding locality group files that include the data items in the columns associated with the respective locality group. In some embodiments, the columns of the table data structure may be grouped into groups of columns and each group of columns is associated with one of a plurality of locality groups. Each locality group is stored as one or more corresponding locality group files that include the data items in the group of columns associated with the respective locality group.