Help needed with xi.include in docbook5 (convert from docbook4)

Hi,

How do I use xi:include in docbook5?

In the main document I have following entry:

<xi:include href="overview/overview.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>

The overview.xml is currently defined as docbook4 (see extract from overview.xls below). May this the problem?

When I try to create the html file

xsltproc --output darktable.html /home/pierre/Downloads/docbook-xsl-1.79.2/xhtml/docbook.xsl darktable.xml

I get following message:

Element include in namespace 'http://www.w3.org/2001/XInclude' encountered in book, but no template matches.

What does the message mean?

And the overview.xml looks like:

<?xml version="1.0" encoding="utf-8"?>

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"

"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [

<!ENTITY % ownChar_dtd SYSTEM "../dtd/ownChar.dtd">

%ownChar_dtd;

]>

<chapter status="final" xml:id="overview_chapter">

....

Thanks

Pierre