Orbeon will generate html for both groups, but one will be hidden. That's correct because group is tied to a variable that could change after model generation (you could place a control, bound to <load-b>, to change value from no to yes).
You can xinclude different xhtml through xpl (
<p:choose> element).
page-flow.xml
<config xmlns="http://www.orbeon.com/oxf/controller">
<page id="load" path-info="*" model="conditional-include.xpl"/>
</config>
conditional-include.xpl<p:config xmlns:p="http://www.orbeon.com/oxf/pipeline"
xmlns:oxf="http://www.orbeon.com/oxf/processors"
xmlns:xforms="http://www.w3.org/2002/xforms">
<!-- Get request parameter 'load-a' and 'load-b' (http://orbeon-server.../?load-a=yes&load-b=no) -->
<p:processor name="oxf:request">
<p:input name="config">
<config>
<include>/request/parameters</include>
</config>
</p:input>
<p:output name="data" id="request"/>
</p:processor>
<p:processor name="oxf:identity">
<p:input name="data"><xforms:group/></p:input>
<p:output name="data" id="empty"/>
</p:processor>
<p:choose href="#request">
<p:when test="/request/parameters/parameter[name = 'load-a']/value='yes' and /request/parameters/parameter[name = 'load-b']/value='yes'">
<p:processor name="oxf:xinclude">
<p:input name="config" href="view.xhtml"/>
<p:input name="model-a-content" href="view-a.xhtml"/>
<p:input name="model-b-content" href="view-b.xhtml"/>
<p:output name="data" id="final-view"/>
</p:processor>
</p:when>
<p:when test="/request/parameters/parameter[name = 'load-a']/value='yes' and /request/parameters/parameter[name = 'load-b']/value='no'">
<p:processor name="oxf:xinclude">
<p:input name="config" href="view.xhtml"/>
<p:input name="model-a-content" href="view-a.xhtml"/>
<p:input name="model-b-content" href="#empty"/>
<p:output name="data" id="final-view"/>
</p:processor>
</p:when>
<p:when test="/request/parameters/parameter[name = 'load-a']/value='no' and /request/parameters/parameter[name = 'load-b']/value='yes'">
<p:processor name="oxf:xinclude">
<p:input name="config" href="view.xhtml"/>
<p:input name="model-a-content" href="#empty"/>
<p:input name="model-b-content" href="view-b.xhtml"/>
<p:output name="data" id="final-view"/>
</p:processor>
</p:when>
<p:otherwise>
<p:processor name="oxf:xinclude">
<p:input name="config" href="view.xhtml"/>
<p:input name="model-a-content" href="#empty"/>
<p:input name="model-b-content" href="#empty"/>
<p:output name="data" id="final-view"/>
</p:processor>
</p:otherwise>
</p:choose>
<p:processor name="oxf:pipeline">
<p:input name="data" href="#final-view"/>
<p:input name="config" href="/config/epilogue.xpl"/>
</p:processor>
</p:config>view.xhtml
<xhtml:html xmlns:xhtml="http://www.w3.org/1999/xhtml"
xmlns:xforms="http://www.w3.org/2002/xforms"
xmlns:fr="http://orbeon.org/oxf/xml/form-runner"
xmlns:xi="http://www.w3.org/2003/XInclude">
<xhtml:head>
</xhtml:head>
<xhtml:body>
<xi:include href="input:model-a-content"/>
<xi:include href="input:model-b-content"/>
<!-- Debugger -->
<fr:xforms-inspector xmlns:fr="http://orbeon.org/oxf/xml/form-runner"/>
</xhtml:body>
</xhtml:html>
view-a.xhtml
<xhtml:html xmlns:xhtml="http://www.w3.org/1999/xhtml"
xmlns:xforms="http://www.w3.org/2002/xforms">
<xforms:group appearance="xxforms:fieldset">
<xforms:label>view-a</xforms:label>
<h1>Text from dynamic inclusion of view-a.xhtml</h1>
</xforms:group>
</xhtml:html>
view-b.xhtml
<xhtml:html xmlns:xhtml="http://www.w3.org/1999/xhtml"
xmlns:xforms="http://www.w3.org/2002/xforms">
<xforms:group appearance="xxforms:fieldset">
<xforms:label>view-a</xforms:label>
<h1>Text from dynamic inclusion of view-b.xhtml</h1>
</xforms:group>
</xhtml:html>
Another way, if your goal is to have a different instance content, is to load instance with an action bound to "xforms-ready" event:
...
<xforms:model id="main-model">
<xforms:instance id="load-model">
<instance>
<load-a>yes</load-a>
<load-b>no</load-b>
</instance>
</xforms:instance>
<xforms:instance id="instance-a">
<dummy/>
</xforms:instance>
<xforms:instance id="instance-b">
<dummy/>
</xforms:instance>
<xforms:submission id="load-instance-a" method="get" resource="instance-a-data.xml" instance='instance-a' replace='instance'/>
<xforms:submission id="load-instance-b" method="get" resource="instance-b-data.xml" instance='instance-b' replace='instance'/>
<xforms:action ev:event="xforms-ready">
<xforms:send if="instance('load-model')/load-a='yes'" submission="load-instance-a"/>
<xforms:send if="instance('load-model')/load-b='yes'" submission="load-instance-b"/>
</xforms:action>
</xforms:model>
...
Locked
include_model.ZIP (1K)