Hi EnthDegree_ and welcome,
We built a loosely coupled (data- or schema-driven) Web service back in 2004 to solve the data normalization problem you are referring to - in other words, rather than build a separate hard-coded Web service for every template, we built one generic Web service that works with all templates. The Web service is called DBXL and there's a free trial available on Qdabra's site. You can definitely look at how we did it. Of course, we've invested significantly in this Web service over the years and now have hundreds of customers using it. We think it's a very low cost way for you to solve the problem of connecting your forms to your SQL database. Saves you money up front because you don't have to create a Web service. Saves you money down-the-road because its been tested over many years in production environments and new templates don't require much more than a data mapping configuration. Take a look at how we did it for ideas - download the trial, read the docs. It's way cheaper than it would take you to write your own and by now it has a ton of extra features and tools that use it.
There's no way to explain how to build a data-driven Web service for InfoPath in one forum post, but I think you have one key idea - the XSF must be linked to the document when you submit it to the Web service so that the Web service knows how to map the data. Of course, you'll need to map the data from XSD to wherever it's going (SQL or a downstream line-of-business process).
At any rate, sorry there's no silver bullet here for you to implement your own, but do take a look at the free trial and you might get ideas for how you can write your own.
Best regards,