Exploring the Client-Server Relationship 311
The Client and the Server
Understanding web applications means that you must also examine the interaction
between client and server that occurs in this environment. A server application is hosted
on a web server and is designed to be accessed remotely via a web browser or web-enabled
application. Typically this environment allows for multiple client applications to access the
server simultaneously, either to retrieve data or to view or modify data. The client performs
minimal processing of information and typically is optimized to present the information to
the user. Information is stored on the server.
So why choose a web application over other client-server models? Well, there are many
potential benefits that arise from this hosting environment over other models. One of the
biggest benefits is that a client application does not have to be developed for each platform
as it would have to be in traditional setups. Since many web applications are designed to be
run within a web browser, the underlying architecture becomes largely unimportant. The
client can be running a wide range of operating systems and environments without penalty
to the application.
Web applications are dependent in many cases on the use of technologies
such as Active Server Pages (ASP), Microsoft ASP.NET, and PHP to allow
them to function. These technologies are referred to as server-side
technologies, which means that they process and manipulate information
on the server. Other technologies such as Dynamic HTML (DHTML),
JavaScript, and related languages are processed on the client, which puts
them in the category of client-side technologies.Most of the commonly encountered web applications are based on the client-server
model and function on a system where data is entered on the client and stored on the server.
Applications such as cloud storage or web-based e-mail services like Yahoo!, Gmail, and
others use this setup as part of their normal functioning.
The past few years have seen the rise of applications for smartphones that perform the
bulk of their processing on the server instead of locally. Google Apps, Microsoft Office
Live, and WebEx WebOffice are examples of the newest generation of web applications.
Closer Inspection of a Web Application
Web applications are designed to run on web servers and send their output over the
Internet. Let’s examine the running of such applications in their environment.
You can visualize a web application not only as consisting of a client and server, but as
layers. These layers are as follows:
Presentation Layer Responsible for the display and presenting of information to the user
on the client side
Logic Layer Used to transform, query, edit, and otherwise manipulate information to and
from the forms it needs to be stored or presented in