Opening SGML

[Serge De Beil]

Hello,

For a new project, we receive a SGML file from our customer.
This SGML file is an export from a database.
What do I need to "parse" this SGML file to Framemaker?

What I've tried is following:
I start Framemaker in Structured Mode.
When I "open" the SGML file, I just get a plain text with all the  
SGML codes in it.
When I use the "Parse Structured Document" function, I'm asked which  
Structured Application I want to use (DocBook, DocBook 2.1, XDocBook  
and XHTML).
I choose one of them, and then I get an error "Could not find  
external document type <name>".

What do I need to open or parse the SGML file in a way that I get a  
decent document with all SGML codes 'interpreted'?

Many thanks in advance.
Serge