Very Computer

I'm using XML to represent some bits of data that I'm passing between
a server and a client. They're actually bits of abstract syntax tree
representing some expressions, but that's not really important here. I
have a DTD which describes what the format of the expressions should
be.

So my XML data looks something like:

<?xml version="1.0"?>
<!DOCTYPE EXPR SYSTEM "expr.DTD">
<EXPR>
...
</EXPR>

I have a couple of questions.

1) I'd like to validate the XML. How do I get the parser to look the
DTD up in some external catalogue? Say I know that the DTD is
available from:

http://somehost/expr.dtd

I guess I use an EntityResolver, but I'm not quite sure how I go about
that.

2) I don't want to go away and have to look the DTD up *every* time I
get one of these things to parse, so is there a way I can pull the DTD
in once and then pass the parser some kind of in-memory object
representing the DTD?

I'm using Sun's Project X Technology Release 1 along with JDK
1.2. Thanks in advance for any assistance.

Cheers,

        Sean B

==========================================================================
| Sean Bechhofer               |                                         |
| Research Fellow              |                                         |
| Information Management Group |                                         |
| Computer Science Department  |                                         |

| Oxford Road                  | Tel: +44-161-275-6145                   |
| Manchester M13 9PL           | Fax: +44-161-275-6932                   |
|------------------------------------------------------------------------|
| WWW: http://potato.cs.man.ac.uk/seanb                                  |
==========================================================================