Here is first xml file input.xml,
input.xml:
<Mapping>
<Common>
<Apps>
<App ID = "id1">
<config key = "Format" value = "PDF"/>
</App>
<App ID = "id2">
<config key = "Logging" value = "no"/>
<config key = "ExtraLogging" value = "no"/>
</App>
</Apps>
<All>
<config key="log1" value="N"/>
</All>
</Common>
</Mapping>
Need to read from input.xml and Add/Remove/update respective entry in output.xml.
output.xml:
<Mapping>
<Common>
<Apps>
<App ID = "id1">
<config key = "Format" value = "DOC"/>
</App>
<App ID = "id2">
<config key = "Logging" value = "yes"/>
</App>
</Apps>
<All>
<config key="log1" value="N"/>
</All>
</Common>
</Mapping>