Hi Claudio,
>I am planning to move my business rule from VCX file (today it is external of my app.) to DLL..

I'ld redesign your plan perhaps.
Calling a COM Dll incurs a much greater overhead
than calling objects directly / from an app.

If there is any chance that quite a few calls need to be made
at one singular time, I'ld opt for calling the business rule objects
directly if I work on a desktop app. Even in web-centered solutions
I'ld keep all code in one COM object if possible -
even in-process DLL's are noticeably slower.

With a little bit more work you can get the same functionality
in COM and normal VFP compiled from the same business sources -
for COM you wrap the objects.

my 0.02 EUR

thomas