Business logic layer - what to use?

[Michael Hipp]

I've got a shot at a job to create a fairly sophisticated vertical app 
for a client. Backend will probably be several Postgresql databases. 
Client side will likely be a custom gui app written in C++ with 
wxWindows (mix of Linux & Windows clients).

What I'm struggling with is what to program the "business logic" in?

Like any transaction-oriented app, there will be lots of data validation 
and cross-checking before committing anything into the db. But writing 
this in something like C++ gives me the creeps.

Suggestions?

Michael