Newbie question

Hello,

I am a newbie, trying to get some pdf-slides out of docbook. Here is my
docbook-xml:
---snip---
<?xml version="1.0" encoding="ISO-8859-15"?>
<!DOCTYPE slides PUBLIC "-//Norman Walsh//DTD Slides XML V3.1.0//EN"
"http://docbook.sourceforge.net/release/slides/3.1.0/schema/dtd/slides.dtd">
<slides>
  <slidesinfo>
    <title>Testslides</title>
  </slidesinfo>
                                                                                
  <foilgroup>
    <title>test Foilgroup</title>
                                                                                
    <foil>
      <title>Test Foil</title>
                                                                                
      <para>test123</para>
    </foil>
  </foilgroup>
</slides>
---snip---

When trying to use the plain.xsl from slides I simly get:
---snip---
You must specify the sf-relid as a parameter.
Processing terminated by xsl:message at line 42
---snip---

What does this mean; what do I need to do?

Thanks in advance
Jochen

--
I love deadlines. I like that swooshing sound they make when they pass
by. -- Douglas Adams 

Jochen Witte
E-mail: 
ICQ: 172361589
pgp-fingerprint: E776 05FC 1DDD DE68 5B8B  4D03 B113 2D76 6135 D10E
Keyserver: http://www.keyserver.net
public-key: http://www.alpha-lab.net/twiki/bin/view/Main/JochenPgpKey