Saxon

The XML parser (Xerces from Apache) is presenting Saxon with a tree as follows:

<root xmlns:xi="...">
   <child xml:base="subfolder/child.xml">
      <otherchild xml:base="subfolder/otherchild.xml"/>
   </child>
</root>

The XML Base specification (§4.3) says: The base URI for a URI reference appearing in an xml:base attribute is the base URI of the parent element of the element bearing the xml:base attribute, if one exists within the document entity or external entity, otherwise the base URI of the document entity or external entity containing the element.

So the base URI for resolving otherchild/@xmlbase is the base URI of child, which is subfolder/child.xml, and this makes the base URI of the otherchild element subfolder/subfolder/otherchild.xml.

I believe that Apache Xerces is getting this wrong, and I don't think there's very much that Saxon can do about it (other than, in extremis, substituting our own implementation of XInclude for the one in Xerces).

The built-in version of Xerces in the Java 8 JDK gives the same result.

I can't comment on the oXygen result. Perhaps they are using their own XInclude processor rather than the Xerces one.

Perhaps we need to read the spec more carefully:

The base URI for a URI reference appearing in an xml:base attribute is the base URI of the parent element of the element bearing the xml:base attribute, if one exists within the document entity or external entity, otherwise the base URI of the document entity or external entity containing the element.

Now "the element bearing the xml:base attribute" isn't actually in any entity, because it's constructed on-the-fly by the XInclude processor, but perhaps this is referring to the original element before it acquired the xml:base attribute, in which case the parent of otherchild is not in the sane entity as child, and therefore perhaps the "otherwise" clause should apply. But the base URI of the entity containing the (original) otherchild element is xxx/subfolder/otherchild.xml, so we still get the same problem.

I'm going to throw this one at the experts on xml-dev.

I believe that you are facing the following bug:

https://issues.apache.org/jira/browse/XERCESJ-1102