Can we consider a design pattern as a tier in j2ee application

Question

Recently i got this question in my interview..

He had asked me about N tier ,I was telling him about 3 tier applications Suddenly he asked me Can i have 5 tiers :) I told him may be but i never used that..

IV: Ok now tell me what can be the 5 tiers ME: BLa bla

After the interview i asked him for the answer and he gave me a example like below

Web or client layer -> delegate(pattern)Ejb layer(business)->value objects(pattern)-Implemenatation of dao layer-then ur db

He added one more point when your application talks with another application then urs will be N tier application

Is it so friends?

Answer 1

I think he confused tiers with layers.

In an architecture, tiers are the coarsest building blocks, seperating concerns like presentation, business logic and persistence, sometimes even in a physical manner. However, a design can introduce additional layers for reasons like reusability, but that doesn't affect the number of tiers the architecture is made of.

Answer 2

Then what can be the 5 tiers?

Answer 3

You can have more than 3 physical tiers, e.g. if you have (1) presentation accessing (2) business logic using (3) web services to wrap (3) legay application which uses a (4) database. But I think like torbengee that it was rather a confusion between logical layer and physical tiers.

Answer 4

Here is an example (I'm not saying follow it, only hardware vendors and application servers vendors like to sell this monster):

1. Client Tier: browser
2. Presentation Tier: Servlet/JSP
3. Service Tier: Session Beans
4. Domain Tier: Entity Beans (writing this makes my eyes bleed).
5. EIS Tier: database

Now, to answer your question, a design pattern is certainly not a tier in itself. But a tier can be made of components implementing a pattern (e.g. the Session Beans of the Service Tier implement the Facade pattern).