Breaking it down further (Client Tier)

As mentioned in my earlier post, the logical tiers that make up "Application Architecture" are (in my mind) the Client Tier, Application Tier, and the Integration (or Data) Tier. Some of the application architecture tiers can be further broken down into logical layers (see my previous blog about how I differentiate between "tiers" and "layers"). Let's start with the Client Tier.

Client Tier
These days, the client tier generally maps to the browser, as is the case with any web application. When referring to "Client-Server" type applications where there is a separate application client program installed on the client machine, things are a little different (and there would be cases where it makes sense to break this down into logical layers), but in the web-world, the client is generally used only as a presentation vehicle for the application user.

The Web 2.0 model has complicated that a bit as well (with AJAX having the potential to move functionality/business logic to the Client Tier). This would be another case where it makes sense to break the tier down into additional logical layers. However, that is a topic for another day.

Thus, the Client Tier (for non-AJAX web applications) is generally responsible for:

• Display of HTML resources
• Issuing HTTP requests for resources,
• Processes HTTP responses

Generally, this means that the Client Tier will be mainly interacting with the Application Tier, sending requests and receiving responses that are then rendered for the user. Pretty straightforward stuff here (except when you bring this whole "Web 2.0" thing and the AJAX that goes along with it).