Matt Gerrans
Posts: 1153
Nickname: matt
Registered: Feb, 2002
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Re: J2EE is a TWO Tier Application What DO You SAY!
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Posted: Oct 8, 2003 10:01 AM
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It doesn't matter how many machines are involved, you could be running a browser right on the server and that doesn't turn it into a 1-tier application. Conversely, you don't do a traceroute and claim you've written a 10-tier application.
The tiers are separation of logic into general subsystems that interact with one another through (hopefully) well-defined interfaces. So in the three-tier scheme, you have 1) the database/persistence, 2) the business logic and then 3) the presentation logic. A two-tier system would be doing database queries directly from the presentation logic (you could do this with JSP or ASP); that is, it would have a combined presentation/business logic tier.
Probably a lot of "3-tier" systems have some bleeding of one tier into another. This is not just because of sloppy design or implementation, either, although it could be. It might be a good performance enhancement. For instance, you might have stored procedures that do some business logic.
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