how find parent app?

[Mark Mitchell]

This is probably a stupid question, but:
I want to be able to open a word processing document with its own parent application.  For example, 

launch file myfile with myApp

Is there a way to automatically determine what myApp should be?  Really, I just
want the file to open as if I had clicked on it in the finder.  So should I be using an appleScript?

thanks,
mark mitchell
japan