>Hi,
> I am wonder that we could build .dll file for implement the business logic to allow public access in 3-tier architecture. Why we put the business logic in .dll? May be it can be accessed by other application, if the logic was designed for an application only, do i still build it in .dll form or vcx? What is the comparison between both in any aspect?? What is the major purposes for each?

A VFP-created .DLL is an in-process OLE Automation server, which can be accessed by an application that supports OLE Automation (and through FPOLE, even some that don't.) A .VCX is a VFP-specific visual class library that can only be accessed from a VFP application; classes in a .VCX declared as OLEPUBLIC can be made available in VFP-created in-process and out-of-process servers.

If you're coding exclusively in VFP, there is no OLE interface overhead in VFP-instantiated classes from a .VCX, and you can use a .VCX to define and subclass visual as well as non-visual classes for use in VFP applications.