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257 lines
7.2 KiB
XML
257 lines
7.2 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.11 $ -->
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<reference id="ref.dba">
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<title>Database (dbm-style) abstraction layer functions</title>
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<titleabbrev>dba</titleabbrev>
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<partintro>
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<section id="dba.intro">
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&reftitle.intro;
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<para>
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These functions build the foundation for accessing Berkeley DB
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style databases.
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</para>
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<para>
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This is a general abstraction layer for several file-based databases.
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As such, functionality is limited to a common subset of features
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supported by modern databases such as
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<ulink url="&url.sleepycat;">Sleepycat Software's DB2</ulink>.
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(This is not to be confused with IBM's DB2 software, which is
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supported through the <link linkend="ref.odbc">ODBC functions</link>.)
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</para>
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</section>
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<section id="dba.requirements">
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&reftitle.required;
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<para>
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The behaviour of various aspects depends on the implementation of the
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underlying database. Functions such as <function>dba_optimize</function>
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and <function>dba_sync</function> will do what they promise for one
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database and will do nothing for others. You have to download and install
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supported dba-Handlers.
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<table>
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<title>List of DBA handlers</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Handler</entry>
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<entry>Notes</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><literal>dbm</literal></entry>
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<entry>
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Dbm is the oldest (original) type of Berkeley DB style
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databases. You should avoid it, if possible. We do not support
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the compatibility functions built into DB2 and gdbm, because
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they are only compatible on the source code level, but cannot
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handle the original dbm format.
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</entry>
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</row>
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<row>
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<entry><literal>ndbm</literal></entry>
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<entry>
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Ndbm is a newer type and more flexible than dbm. It still has
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most of the arbitrary limits of dbm (therefore it is
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deprecated).
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</entry>
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</row>
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<row>
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<entry><literal>gdbm</literal></entry>
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<entry>
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Gdbm is the <ulink url="&url.gdbm;">GNU database
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manager</ulink>.
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</entry>
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</row>
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<row>
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<entry><literal>db2</literal></entry>
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<entry>
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DB2 is <ulink url="&url.sleepycat;">Sleepycat Software's
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DB2</ulink>. It is described as "a programmatic toolkit that
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provides high-performance built-in database support for both
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standalone and client/server applications.
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</entry>
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</row>
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<row>
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<entry><literal>db3</literal></entry>
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<entry>
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DB3 is <ulink url="&url.sleepycat;">Sleepycat Software's
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DB3</ulink>.
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</entry>
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</row>
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<row>
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<entry><literal>db4</literal></entry>
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<entry>
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DB4 is <ulink url="&url.sleepycat;">Sleepycat Software's
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DB4</ulink>. This is available since PHP 5.0.0.
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</entry>
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</row>
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<row>
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<entry><literal>cdb</literal></entry>
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<entry>
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Cdb is "a fast, reliable, lightweight package for creating and
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reading constant databases." It is from the author of qmail and
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can be found <ulink url="&url.cdb;">here</ulink>. Since it is
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constant, we support only reading operations. And since PHP 4.3.0
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we support writing (not updating) through the internal cdb library.
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</entry>
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</row>
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<row>
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<entry><literal>cdb_make</literal></entry>
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<entry>
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Since PHP 4.3.0 we support creation (not updating) of cdb files
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when the bundeled cdb library is used.
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</entry>
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</row>
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<row>
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<entry><literal>flatfile</literal></entry>
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<entry>
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This is available since PHP 4.3.0 for compatibility with the deprecated
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<link linkend="ref.dbm">dbm</link> extension only and should be avoided.
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However you may use this where files were created in this format. That
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happens when configure could not find any external library.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</para>
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<para>
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When invoking the <function>dba_open</function> or
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<function>dba_popen</function> functions, one of the
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handler names must be supplied as an argument. The actually
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available list of handlers is displayed by invoking
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<function>phpinfo</function> or <function>dba_handlers</function>.
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</para>
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</section>
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&reference.dba.configure;
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<section id="dba.runtime">
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&reftitle.runtime;
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&no.config;
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</section>
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<section id="dba.resources">
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&reftitle.resources;
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<para>
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The functions <function>dba_open</function> and
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<function>dba_popen</function> return a handle to the specified
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database file to access which is used by all other dba-function calls.
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</para>
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</section>
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<section id="dba.constants">
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&reftitle.constants;
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&no.constants;
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</section>
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<section id="dba.examples">
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&reftitle.examples;
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<para>
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<example>
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<title>DBA example</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$id = dba_open ("/tmp/test.db", "n", "db2");
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if (!$id) {
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echo "dba_open failed\n";
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exit;
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}
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dba_replace ("key", "This is an example!", $id);
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if (dba_exists ("key", $id)) {
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echo dba_fetch ("key", $id);
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dba_delete ("key", $id);
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}
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dba_close ($id);
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<para>
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DBA is binary safe and does not have any arbitrary limits.
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However, it inherits all limits set by the underlying
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database implementation.
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</para>
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<para>
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All file-based databases must provide a way of setting the file
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mode of a new created database, if that is possible at all. The
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file mode is commonly passed as the fourth argument to
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<function>dba_open</function> or <function>dba_popen</function>.
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</para>
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<para>
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You can access all entries of a database in a linear way by using the
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<function>dba_firstkey</function> and <function>dba_nextkey</function>
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functions. You may not change the database while traversing it.
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</para>
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<para>
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<example>
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<title>Traversing a database</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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// ...open database...
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$key = dba_firstkey ($id);
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while ($key != false) {
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if (...) { // remember the key to perform some action later
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$handle_later[] = $key;
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}
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$key = dba_nextkey ($id);
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}
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for ($i = 0; $i < count($handle_later); $i++)
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dba_delete ($handle_later[$i], $id);
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?>
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]]>
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</programlisting>
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</example>
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</para>
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</section>
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</partintro>
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&reference.dba.functions;
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</reference>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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