A quick dope on how Application Architectures have evolved from 2-tier to "gear-tier"

1. Application Architecture
An Introduction

2. 2-Tier Architecture
Database
Clients made
in IDE’s like
Visual Basic

3. 3-Tier Architecture

4. Web Based Model is essentially a
3-tier architecture
Browser
Web Server
(PHP / ASP)
Database
(MySQL, Oracle)

5. The latest Application Architecture
paradigm is
XML / JSon
Presentation Layer
Business Logic
or or
API
Layer
Data Layer
(PHP / ASP)
(HTML / JavaScript) Custom Messaging
Format

6. Result
• Any web based application is written as two independent
applications
– HTML Pages (with Jscript code) which define how the User
Interface will look like
– PHP / ASP pages which send / receive and process data
• The HTML and PHP pages exchange information using
XML / JSon or a custom developed messaging format
(plain text)
• Each HTML page loads, it sends data request to a PHP
page using Ajax and receives data and updates the
information on the page
• The PHP pages act like an Application programming
Interface (API) which receive requests from HTML pages
and send back raw data to them.

7. What Google Says
Source: http://code.google.com/apis/gears/architecture.html
In most web applications today there is no real data layer.
Figure: No data layer
In general, isolating the data layer is a good first step.
When you add a local datastore to your application, you will have a single place through
which all data storage and retrieval requests pass.

8. The Next Stage
(for offline availability)