>I've always developed single-tier FP/VFP apps. I've been meaning to try out some C/S stuff for at least two years (honest!), but now it looks like I should go straight to three tier for the in-house project we'll be starting in a few months. So I have a couple of questions.

3-tier is an excellent way to go. There really are limitations in the two-tier model.

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>First, can anyone point me to the incurably self-taught programmer's guide to 3-tier development, if there is one?


Jim Booth has one on his web site. You should also look at the book Designing Component-based Applications from Microsoft Press.

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>Second, can anyone answer a couple of very basic questions:
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>1. When we say that the back end handles integrity, do we really mean only relational integrity? No business rules and no triggers? To me and my single-tier background, integrity was always synonymous with FP-style validation. That is, it handles relational integrity, business rules, and triggers that run after a user changes a value.

Data handles referential integrity. If triggers are needed to do that, then you have triggers.

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>2. The middle tier is for business rules, then, right? Such as, can't save the sales order if the customer is over credit limit. Also, the triggers go here? Such as, user has entered a sales tax code, recalculate the total value of the sales order.

Business Rules and data validation are handled in the middle tier. Your example of not saving the sales order is correct. Do triggers go here? If the triggers enforce referential integrity, then no. If they require a specific process to happen, then yes, they belong here.


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>3. Finally, then, the front end is just to submit queries and updates to the middle, and report middle-layer errors to the user?

Display only. You may have some minor data validation, such as a field can't be blank, but that's the extent of validation at this point.


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>As always, TIA...