||Abstract database is a set of interfaces to use on-memory hash database, on-memory tree
database, hash database, B+ tree database, fixed-length database, and table database with the
||B+ tree database is a file containing a B+ tree and is handled with the B+ tree database API.
||Cursor is a mechanism to access each record of B+ tree database in ascending or descending
||Fixed-length database is a file containing an array of fixed-length elements and is handled
with the fixed-length database API.
||Hash database is a file containing a hash table and is handled with the hash database API.
||Table database is a file containing records composed of the primary keys and arbitrary columns
and is handled with the table database API.
||Query is a mechanism to search for and retrieve records corresponding conditions from table
||Set of utility methods.