Difference between three tier vs. n-tier

Question

I just came across the following sentence:

As the industry has moved from a three tier model to n-tier models, the object relational impedance mismatch

Answer 1

n-tier implies n is any number - when n=3 then it is the same as n-tier.

The usual definition of 3-tier is presentation, logic & data (in any order), and yes, SOA can confuse the neophyte because sometimes it sits in the data tier, sometimes the logic tier and sometimes both logic & data tiers.

The whole subject is...subjective. If you need some tiers then call it n-tier - if you know that n=7 then call it 7-tier, or n-tier.

Answer 2

The quote appears to be from this codeproject page. It also seems to do a pretty good job of explaining n-tier to include things like web services, javascript, workflows, etc. All things that 3-tier models don't necessarily include.

Answer 3

hi pls check this link, so u can get good idea regarding this

http://msdn.microsoft.com/en-us/library/ms973829.aspx

Answer 4

This Wiki-book chapter on application architecture is a straightforward guide to layers, tiers, and deciding what you need to use.

Answer 5

Hey I can't even get a definition of 3 tier. Sometimes they discount javascript on the client and sometimes javascript on the client and the client web browser are considered another tier. So an ASP page that talks to a database can be 3 tier if you assume database = tier 3, web server = tier 2, client web browser = tier 1. And other times web server = tier 1, middleware = tier 2, database = tier 3. It really depends who is writing the definition/book.

In general n-tier seems to refer splitting the middleware layer up more. But aside from that I don't see consistent definitions.

Answer 6

Where is that quote from? What industry are they referring to? I would have to imagine that this has something to do with SOA because that is the only thing that makes sense for this kind of statement.

Most people that I have heard who make this kind of statement believe that in a service-oriented domain each service is somehow its own tier. I disagree as most of the time these disparate services can be logically grouped into the common three tiers anyhow (presentation, logic, and data). But again, its all pretty subjective.