2.2. Data Entry Concepts  When entering data in GnuCash, you
should be aware of the 3 levels of organization in which GnuCash
divides your data: files, accounts and transactions. These
levels are presented in their order of complexity, one file
contains many accounts and one account contains many
transactions. This division is fundamental to understanding how
to use GnuCash.  2.2.1. Files  GnuCash stores information at the
highest level in files. A file can be stored on your computer
either as a single XML file (in all versions of GnuCash), or in
a SQL database (in GnuCash version 2.4 and higher).   SQL is
pronounced sequel, so in spoken and written language we would
say a SQL database.  With the XML file format, GnuCash stores
your data in an XML data file, usually in compressed format
(although this can be changed in the General tab of the GnuCash
Preferences).  With SQL storage, GnuCash stores your data in a
SQL database under the database application you select (SQLite3,
MySQL or PostgreSQL).  You will ne