XML identity references

I am creating an interface based on a card layout.  I would like to
put the view in each card into a different XML file using entity
references, like so:

<?xml version="1.0"?>
<!DOCTYPE swixml
	[
		<!ENTITY foo SYSTEM "foo.xml">
		<!ENTITY bar SYSTEM "bar.xml">
	]>

<frame size="480, 360" title="Hello SWIXML World"
DefaultCloseOperation="JFrame.EXIT_ON_CLOSE">
	
	<panel Layout="CardLayout(15, 15)">
	&foo;
	&bar;
	</panel>

</frame>

This leads to the following error:   
org.jdom.input.JDOMParseException: Error on line 4: Relative URI
"foo.xml"; can not be resolved without a base URI.

All of the xml files are in the same directory, but I guess the parser
isn't smart enough to look there for them.   How do I specify the base
URI?

thanks in advance