These functions build the foundation for accessing Berkeley DB style
databases.

This is a general abstraction layer for several file-based databases. As
such, functionality is limited to a common subset of features supported
by modern databases such as Sleepycat Software's DB2. (This is not to be
confused with IBM's DB2 software, which is supported through the ODBC
functions.)

This extensions allows to work with the following databases:
dbm      DBM is the oldest (original) type of Berkeley DB style databases.
         You should avoid it, if possible. We do not support the
         compatibility functions built into DB2 and gdbm, because they are
         only compatible on the source code level, but cannot handle the
         original dbm format.
ndbm     NDBM is a newer type and more flexible than dbm. It still has
         most of the arbitrary limits of dbm (therefore it is deprecated).
gdbm     GDBM is the GNU database manager.
db2      DB2 is Sleepycat Software's DB2. It's described as "a programmatic
         toolkit that provides high-performance built-in database support
         for both standalone and client/server applications.
db3      DB3 is Sleepycat Software's DB3.
db4      DB4 is Sleepycat Software's DB4. This is available since PHP 5.0.
cdb      CDB is "a fast, reliable, lightweight package for creating and
         reading constant databases." It is from the author of qmail and
         can be found at http://cr.yp.to/cdb.html. Since it is constant,
         we support only reading operations. And since PHP 4.3.0 we support
         writing (not updating) through the internal cdb library.
cdb_make Since PHP 4.3.0 we support creation (not updating) of cdb files
         when the bundled cdb library is used.
flatfile This is available since PHP 4.3.0 for compatibility with the
         deprecated dbm extension only and should be avoided. However you
         may use this where files were created in this format. That happens
         when configure could not find any external library.
inifile  This is available since PHP 4.3.3 to be able to modify php.ini
         files from within PHP scripts. When working with ini files you
         can pass arrays of the form array(0=>group,1=>value_name) or
         strings of the form "[group]value_name" where group is optional.
         As the functions dba_firstkey() and dba_nextkey() return string
         representations of the key there is a new function dba_key_split()
         available since PHP 5 which allows to convert the string keys into
         array keys without losing FALSE.
qdbm     This is available since PHP 5.0.0. The qdbm library can be loaded
         from http://qdbm.sourceforge.net.


After configuring and compiling PHP you must execute the following test
from commandline:
  php run-tests.php ext/dba.
This shows whether your combination of handlers works. Most problematic
are dbm and ndbm which conflict with many installations. The reason for
this is that on several systems these libraries are part of more than one
other library. The configuration test only prevents you from configuring
malfaunctioning single handlers but not combinations.
