What is ASP.NET?
For years, the Active Server Pages (ASP) technology was arguably the leading
choice for web developers building dynamic web sites on Windows web servers,
as it offered flexible yet powerful scripting capabilities. Early in 2002, Microsoft
released a new technology for Internet development called ASP.NET. ASP.NET
represents a leap forward from ASP both in its sophistication and the productivity
gains it achieves for developers. It continues to offer flexibility in terms of language
support, but rather than a range of simple scripting languages, several fully-fledged
programming languages are now at the fingertips of ASP.NET developers. Devel-
opment in ASP.NET requires not only an understanding of HTML and web
design, but also a firm grasp of the concepts of object oriented programming and
In the next few sections, well introduce you to the basics of ASP.NET. Well
walk through the process of installing it on your web server, and step through a
simple example that demonstrates how ASP.NET pages are constructed. But first,
lets define what ASP.NET actually is.
ASP.NET is a server-side technology for developing web applications based on the Microsoft
.NET Framework. Lets break that jargon-filled sentence down.
ASP.NET is a server-side technology; that is, it runs on the web server. Most web
designers start their careers learning client-side technologies like HTML, JavaS-
cript, and Cascading Style Sheets (CSS). When a web browser requests a web
page created with only client-side technologies, the web server simply grabs the
files that the browser (or client) requests and sends them down the line. The client
is entirely responsible for reading the markup in those files and interpreting that
markup to display the page on the screen.
Server-side technologies, like ASP.NET, are different. Instead of being interpreted
by the client, server-side code (for example, the code in an ASP.NET page) is
interpreted by the web server. In the case of ASP.NET, the code in the page is
read by the server and used to generate HTML, JavaScript, and CSS that is then
sent to the browser. Since the processing of the ASP.NET code occurs on the
server, its called a server-side technology. As Figure 1.1 shows, the client only
sees the HTML, JavaScript, and CSS. The server is entirely responsible for pro-
cessing the server-side code.
Chapter 1: Introducing ASP.NET and the .NET Platform
Figure 1.1. A user interacting with a web application
Note the three roles involved in such a transaction:
Never forget that theres a real person at the end (or beginning)
of the line.
web client
This is the software program that the person uses to interact to
the web application. The client is usually a web browser, such as
Internet Explorer or Firefox.
web server
This is the software program located on the server. It processes
requests made by the web client.
ASP.NET is a technology for developing web applications. A web application is just a
fancy name for a dynamic web site. Web applications usually (but not always)
store information in a database, and allow visitors to the site to access and change
that information. Many different programming technologies and supported lan-
guages have been developed to create web applications; PHP, JSP, Ruby on Rails,
What is ASP.NET?

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