Multi-tier architecture

[Massimo Sperossi]

It is not clear to me if the 3-tier/n-tier concepts are related to software architecture, hardware architecture or both.

The wikipedia page starts with
In software engineering, multi-tier architecture (often referred to as n-tier architecture) is a client–server architecture in which the presentation, the application processing, and the data management are logically separate processes.
It use "software" word, thus is it speak about software architecture?

But sometimes it seems to speak about hardware, for example
... a layer is a logical structuring mechanism for the elements that make up the software solution, while a tier is a physical structuring mechanism for the system infrastructure
and
Data Tier. This tier consists of database servers. Here information is stored and retrieved.

What is yours thought?

If I have a classical j2ee application with jsp/servlets (presentation tier) and EJBs (business tier) and I deploy web container and EJB container in the same single app server in the same single physical server, is this 2 tier or 3 tier?
And if I have the RDBMS in the same single physical server too, this is 3, 2 or 1 tier?

[Henry Naftulin]

I think it is somewhat of both. In your case, you chose to deploy it on server - but your architecture allows it to be deployed to several servers: the web components could go to web server, and EJB components could live on a application server. Usually, in J2EE application, you would also access database, which can live in its own server box, right? So, in classical J2EE architecture you have 3 tiers, even when you choose to collapse some of them for the time being.

Hope that helps,

Henry

[Massimo Sperossi]

Thank you, you help.

I think the same of you, but I was not sure and want other people confirmations