[Zope] What am I doing wrong?

[Glenn Rogers]

Warning - newbie alert!  I'm playing around with zope to see what it
does and have come up with a problem that I don't understand.

I have an sql method sqlSelectTopic which returns 'topic':

    select * from topic_table 

I have another sql method sqlSelectSiteByTopic:

    argument 'topic'
    select * from site_table where topic = '<dtml-var topic>'

In another method:

    <!--#in sqlSelectTopic-->
      <h3><!--#var topic--></h3>
      <!--#in sqlSelectSiteByTopic-->
        <p><!--#var href_from_site_table--></p>
      <!--#/in-->
    <!--#/in-->

Whereupon I get (from sqlSelectSiteByTopic ???):

    Error Type: Bad Request
    Error Value: ['topic']

It was my understanding that the 'topic' returned from sqlSelectTopic
would be used by sqlSelectSiteByTopic, but this seems to be wrong. 
Whats going on?  How can I get it to behave?


Thanks for your help, 

Glenn