University of Wisconsin-Madison CS 638 Web Programming
Lecture 1 – Introducing the web
The web started out as a distributed solution for accessing through the Internet documents
hosted by various organizations on their servers. The most revolutionary feature of the
web is that it allows the documents to contain hyperlinks pointing to other documents on
a server somewhere on the Internet. These hyperlinks (for short links) form a global web
of connected documents hence the name “the world-wide web”.
Today’s web is much more than a distributed repository of static documents. Clients can
send information to the servers, web pages can be generated dynamically, and rich forms
of interaction between the user and the web client are supported. The web has become the
dominant method for interacting with server-based computerized systems. Web-based
applications range from publicly accessible weather forecasting pages to complex
systems tracking everything from customer information to inventories of spare parts that
allow companies large and small to function more efficiently.
At the core of the technical definition of the web are the rules for encoding the web
documents and the rules for how the client and the server software interact with each
other (called protocol). To be able to build web applications one also needs to understand
what the web client and the server do and how they can be extended. This lecture gives a
brief introduction into these four central topics. Future lectures will address each of them
in more detail.
The web client software
The term web client can be used to denote the computer a user uses to access the web, or
the software on that computer that is used to access the web. In this class we most often
use the second meaning and it should be clear from the context what we mean. The web
client software, also called the web browser, is a complex program. Its main goal is to
request and receive web pages from various servers as directed by the user and to render
(to display) them. Protocols describe the rules for how the browser interacts with the
server. Various standards describe how it should display the documents it receives.
Unfortunately, to build web pages one needs not only understand the standards for
displaying documents, but also to some extent how various browser implementations
behave. There are small details about how documents should be displayed that the
standards do not specify. Individual browser implementations sometimes make different
choices. It is also common for browsers to use non-standard extensions. It is not
uncommon for later versions of standards to incorporate popular browser-specific
extensions. Currently the dominant browsers are various versions of Microsoft’s Internet
Explorer and various browsers based on open-source the Mozilla core such as Firefox.
Apple’s Safari and Opera are also used by a significant number of people. Some browser
variants are specifically customized to operate on handheld devices (personal digital
assistants, mobile phones). Compared to desktop or laptop computers, these devices have
smaller screens, less memory, weaker processors, and more limited forms of user
Cristian Estan and Perry Kivolowitz, last updated on 9/1/2007 1/4
