call with mapping function

Hallo at all!

My problem is the way of work from Tamino.

I have developed two functions for Server extensions. One is a mapping function and the other is a query function, The mapping function recalls data from another database to the node of my schema instance. The query function ?molsel? gets two parameters. First is a node entry from the Instance with the mapping function (but not the node which is mapped). The other has no influence of my problem.
My query looks like that:

CGI[CGIPart= molsel(/CGI/CGIPart, 'parameter?)]/
or
CGI[CGIRoot/CGIPart= molsel(/CGI/CGIRoot/CGIPart, 'parameter?)]/

And now for all Instances of /CGI/CGIPart or /CGI/CGIRoot/CGIPart Tamino makes a call with the mapping function. I tried it with schemas like:

-CGI
CGIPart
anything
CGIRoot
CGINo with mapping function

-CGI
CGINo with mapping function
Anything
CGIRoot
CGIPART

By both it is the same, Tamino calls the mapping function although the node with this function is not the Parameter.

I hope anybody can help me.

Kind regard

Elke