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Combining XML Documents and Fragments Using XInclude

XInclude is a standard for assembling XML instances into another XML document through inclusion. A main file can be dynamically created from smaller XML documents without having to physically duplicate the content of the smaller files. The advantage of using XInclude instead of the DTD Entities method is that each of the assembled documents is permitted to contain a Document Type Declaration (DOCTYPE). This means that each file is a valid XML instance and can be independently validated. It also means that the main document, which includes smaller instances, can be validated without having to remove or comment out the DOCTYPE (as is the case with External Entities).

Enabling XInclude Support in Oxygen XML Author

The XInclude support in Oxygen XML Author is enabled by default. It is controlled by the Enable XInclude processing option in the XML > XML Parser preferences page. When enabled, Oxygen XML Author will be able to validate and transform documents comprised of parts added using XInclude.

Example: Using XInclude to Combine Files

A chapter file (introduction.xml) looks like this:

<?xml version="1.0"?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
"http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">
<chapter>
    <title>Getting started</title>
    <section>
        <title>Section title</title>
        <para>Para text</para>
    </section>
</chapter>

The main article (main file) looks like this:

<?xml version="1.0"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
"http://www.docbook.org/xml/4.3/docbookx.dtd"
[ <!ENTITY % xinclude SYSTEM "../frameworks/docbook/dtd/xinclude.mod">
%xinclude;
]>
<article>
    <title>Install guide</title>
    <para>This is the install guide.</para>
    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" 
                    href="introduction.xml">
      <xi:fallback>
        <para>
          <emphasis>FIXME: MISSING XINCLUDE CONTENT</emphasis>
        </para>
      </xi:fallback>
    </xi:include>
</article>

In this example, note the following:

The DOCTYPE declaration defines an entity that references a file containing the information to add the xi namespace to certain elements defined by the DocBook DTD.
The href attribute of the xi:include element specifies that the introduction.xml file will replace the xi:include element when the document is parsed.
If the introduction.xml file cannot be found, the parser will use the value of the xi:fallback element - a FIXME message.

Example: Using XInclude to Combine Fragments of Files

If you want to include only a fragment of a file in the main file, the fragment must be contained in a tag having an @xml:id attribute and you must use an XPointer expression pointing to the @xml:id value.

Notice: Oxygen XML Author supports the XPointer Framework and the XPointer element() Scheme, but it does NOT support the XPointer xpointer() Scheme.

For example, if the main file is:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-model href="test.rng" type="application/xml" 
        schematypens="http://relaxng.org/ns/structure/1.0"?>
<test>
    <xi:include href="a.xml" xpointer="a1"
        xmlns:xi="http://www.w3.org/2001/XInclude"/>
</test>

and the file (a.xml) is:

<?xml version="1.0" encoding="UTF-8"?>
<test>
    <a xml:id="a1">test</a>
</test>

after resolving the XPointer reference, the document is:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-model href="test.rng" type="application/xml" 
          schematypens="http://relaxng.org/ns/structure/1.0"?>
<test>
    <a xml:id="a1" xml:base="a.xml">test</a>
</test>

Viewing the Expanded Content in Oxygen XML Author

When a transformation scenario is applied on the main file, an intermediary file combines all the referenced content and it will be expanded in the final output. If you want to see how the referenced content will be expanded before applying the transformation, you can do one of the following:

Simply switch to Author mode.

Create a minimal XSLT stylesheet that simply copies the XML content, then create a new XSLT transformation scenario that applies the stylesheet over the XML. The XSLT stylesheet would look like this:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:math="http://www.w3.org/2005/xpath-functions/math"
    exclude-result-prefixes="xs math"
    version="3.0">
    <xsl:template match="node() | @*">
        <xsl:copy>
            <xsl:apply-templates select="node() | @*"/>
        </xsl:copy>
    </xsl:template>
    
</xsl:stylesheet>

XInclude 1.1 Features

Oxygen XML Author offers partial support for XInclude 1.1 features. This includes support for fragment identifiers and attribute copying.

Fragment Identifiers

You can use <xi:include> to reference a text file and specify the @fragid value so that you only get part of that text file in the main document. For some examples and to see how the <xi:include> gets expanded when the @fragid specifies a line range or character range, see Textual Inclusion Examples with RFC5147 Fragment Identifiers.
Attribute Copying

Any namespaced attribute defined on the <xi:include> element will be passed to the root element of the included content.
For example, if you have this:
```
<xi:include href="section2.xml" xmlns:xi="http://www.w3.org/2001/XInclude" 
  set-xml-id="sectInner1"/>
```
and section2.xml looks like this:
```
<sect2 xmlns="http://docbook.org/ns/docbook" version="5.0"
    xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="section2">
    <title>FS2</title>
    <para>P2</para>
</sect2>
```
then the final processed result will have the original xml:id="section2" replaced with the value specified in the xi:included section.

For more information, see Attribute Copying when Processing XML. Also, to see more examples, see Attribute Copying Examples.