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<?xml version="1.0" encoding="ISO-8859-1"?>
<!--
-
- This file is part of the OpenLink Software Virtuoso Open-Source (VOS)
- project.
-
- Copyright (C) 1998-2018 OpenLink Software
-
- This project is free software; you can redistribute it and/or modify it
- under the terms of the GNU General Public License as published by the
- Free Software Foundation; only version 2 of the License, dated June 1991.
-
- This program is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- General Public License for more details.
-
- You should have received a copy of the GNU General Public License along
- with this program; if not, write to the Free Software Foundation, Inc.,
- 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
-
-
-->
<refentry id="xpf_id">
<refmeta>
<refentrytitle>id</refentrytitle>
<refmiscinfo>XPATH</refmiscinfo>
</refmeta>
<refnamediv>
<refname>id</refname>
<refpurpose>Returns an entities whose ID attributes are in the given list</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis id="xpf_syn_id">
<funcprototype id="xpf_proto_id">
<funcdef>sequence <function>id</function></funcdef>
<paramdef><parameter>ids</parameter> any</paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 id="xpf_desc_id"><title>Description</title>
<para>
The function gets a list of strings, where every string is a list of IDs delimited by whitespace characters.
For every listed ID, the function checks if the document that contains the context entity also contains
an entity with such ID; if the entity with the listed ID exists, it is added into the sequence.
</para>
<para>
To avoid searches of every ID inside the whole document, the function uses "ID cache" that is
created if "IdCache=ENABLE" DTD configuration option is specified in the call of function that
parses the XML document. In some cases, it is possible to build such cache on demand if it is not built
by a parser, but it consumes time and in any case it requires the saved DTD information from the XML parser,
so the parser should be specially configured anyway.
</para>
<para>
Note that any attribute of types ID, IDREF or IDREFS is a good input string for the function id().
So while XQuery "pointer operator" is not available in XPath expression, the id() function
is a good replacement for it.
</para>
</refsect1>
<refsect1 id="xpf_params_id"><title>Parameters</title>
<refsect2><title>ids</title>
<para>The list of strings that consist of IDs</para></refsect2>
</refsect1>
<refsect1 id="xpf_ret_id"><title>Return Types</title><para></para></refsect1>
<refsect1 id="xpf_errors_id"><title>Errors</title>
<para>The function ignores any sort of syntax errors on input.</para>
</refsect1>
<refsect1 id="xpf_examples_id"><title>Examples</title>
<example id="xpf_ex_id"><title>List errors in census data</title>
<para>List every person who is not a spouse of his own spouse.</para>
<screen>document ("census.xml")//person[@spouse and not (. = id (id (@spouse)/person/@spouse)]</screen>
</example>
</refsect1>
<refsect1 id="xpf_seealso_id"><title>See Also</title>
<para><link linkend="xpf_document">document()</link></para>
</refsect1>
</refentry>
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