Wow this was a mouthful. I have many of these same scenarios and need to understand best way to size it. I use the NESMA Estimated sizing method.
I use USPS to validate address so in this case, it seems I would have an EIF (for the address that USPS is going to return to me) and an EQ for the USPS address returned to the customer at the request of validation (in other words, the EQ which is what the user see’s as the USPS address and can select it or keep the one they entered) and an EIF for the address that USPS keeps and maintains. As far as an additional EQ (which is the message from my system to the USPS web service) and the EI (for the message back with the valid address)…I am choosing to not count these separately as they are part of the primary EQ that the customer receives as the USPS address to use or keep what customer entered into the system.
I also use Google maps to verify address is valid and to see where to deliver. I would imagine it is counted the same as the USPS scenario above.
Frank, I looked back at my rules and here is what we captured as far as using a web service or application for the back end.
When data is being passed (not owned or maintained by the system being counted) to a web service or another layer, we consider these systems as part of the same system so in this case we consider an ILF, and EI/EO/EQ.
When data is stored or referenced in the system being counted and in turn the data is passed to a web service or another application, we consider these systems as separate so in this case we consider an ILF and EI/EO/EQ for the main system and also EI/EO for the communication with the other system (or user in this case). Additionally, an EIF is considered for the permanent data returned to the main system.
So for the above example, it would fall into my second paragraph since the address entered is stored in the main system and passed on to USPS for validation (and once confirmed is replaced with the address from USPS or not depending on the users response). So in this case the EI/EO would be considered along with the EIF.