Chapter 2- Cyganski book

Monica Stoica

Boston University

First need for the Web

• The Web was developed originally to solve a very specific problem; fortunately, it turned out to be useful for many other problems and needs as well.

• It was created to facilitate communications among nuclear physicists located throughout the world.

• These physicists make use of data gathered at specialized facilities, such as CERN (European Particle Physics laboratory) in Geneva, Switzerland, and LANL (Los Alamos National Labs) in the United States.

Email first• Thus, physicists need to communicate with each

other so that they can share analyses and hypotheses and to transfer experimental data to their own locations for analysis.

• these transactions should be rapid, and they should be able to convey information containing a mixture of text, graphics, images, and mathematics.  

• The first new communication tool to benefit these physicists in their work was e-mail. Originally, e-mail only provided for the sending of what is often called raw text between correspondents.

MIME• E-mail evolved during the first twenty years of the

operation of the Internet to address the needs of those who wished to send copies of material different than raw text.

• In 1991, a system known as MIME (Multi purpose Internet Mail Extensions) was introduced to allow e-mail users to make attachments of additional documents to an e-mail.

• Why was the MIME system needed; couldn't the mail-reader software application just be extended to read and display all the documents?• Why wasn't the MIME solution alone good enough to address the

needs that we have been considering?

No MIME?

• There were two main problems with extending the original e-mail system directly to read all possible document types:

• There are too many people simultaneously inventing too many things during this information age for any single e-mail system to supply means to handle all the possible variations of document types and related displayers. Document types, image types, multimedia content, and so forth, are all products of human invention and human convention. Thus, there is almost no end to the variations of content type and variations of ways to package and transmit that content (using the technologies that we will consider in the following chapters).

Email not enough?• For every document type display system, there may

be dozens of displayers that have been created, each expressing some personal preference, and a group of followers who want access to the displayer that suits their preference.

• Thus, the MIME e-mail extension technology was developed.

• To understand why the existence of this technology still did not satisfy the general needs of most people and organizations, we need to consider how it would be used in a common situation.

Why have the WWW?• Suppose that you are part of a fairly large

organization; this could be a formal organization such as the physicists at CERN, or an informal one such as a group of English-speaking cat lovers throughout the world who share experiences, pictures, and so forth.

• Further suppose that you have an observation you would like to share with members of your scientific group that includes some images and data. So, you write an e-mail that explains your observations, attach a set of pictures and graphs to the e-mail, and then send it.

Responses to your email!• Several of your recipients, who don't really share your

intense interest,simply delete the material and send e-mail to you indicating that they should be left off your future e-mail list because it took several minutes of precious time for your large, image-laden e-mail file to download over their slow telephone connection to the Web.

• Other recipients read your e-mail, but they suffer the need to display the various components of the package and try to figure out which images you are referring to, because the images and the text are not directly connected in any way. Some readers, in fact, completely misunderstand the observation you are making because of this confusion and attack your theory.

Responses• Still other recipients tell friends and colleagues about your

observations. This news spreads by word of mouth, and nearly every day for a month you get an e-mail from someone asking you to assemble and send the same e-mail package to them.

• Furthermore, others write their own e-mails about what your e-mail led them to try in their own laboratories. Soon, a slew of e-mail is flying across the Internet with cross references that would take a monumental effort to unwind back to your seminal message.

• Finally, when new people join the group, they are completely unaware of your work. They may go on to replicate your work, or lose time by asking around until they encounter a rumor about your observations, eventually leading to yet another request for that e-mail you composed several years ago.

We need the web

• The problem we have outlined in this example is connected with the need for asynchronous access (at any time, from any place) to stored and indexed (organized in some logical way) information that can include a wide variety of content types with some clear association between the various content components.

• In the following discussion we will see how the World Wide Web answers these needs when we revisit the above example.

Tim Berners-Lee• The WWW was the brainchild of Tim

Berners-Lee, an Oxford University graduate working at the CERN facility, who is now Director of the World Wide Web Consortium(W3C ).

• Berners-Lee undertook the task of finding a simple, extendible, and distributed approach to solving the communication problems of the particle physicists described above.

A Web Server• in 1992 the CERN team introduced the first version

of a Web browser, along with the required Web server software.

• An Internet Web server is a software application that executes on a computer connected to the Internet and offers a service to other computers on the Internet.

• The purpose of a Web server is to receive requests for information from Web browsers, and to send, via the Internet, the requested documents (a term we will use to refer to any content type).

Web Browsers• In the early 1990s, the programmers at the National Center

for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign (funded by the National Science Foundation) saw the utility of this communication technology and undertook writing their own improved Web browser. However, they developed it on a generic software base, so that it would be transport able to the much larger number of Unix operating system based work stations in use by scientific users.

• The Mosaic Web browser introduced extensive graphical rendering and text font and format flexibility. Mosaic 1.0 for the UNIX Xwindows was introduced in April of 1993, and it ignited the interest of computer users throughout the world.

Netscape• By late 1993, Version 2.0 had been released, and

versions for the PC and Apple McIntosh were introduced.

• The lead programmer in the effort to create Mosaic, Marc Andreessen, soon left NCSA along with several others from the team to form the company Netscape Communications.

• Here they developed the Netscape Navigator Web browser that was to catapult the Web to fame. Since then, the Web has become an essential tool on computers in homes, businesses, and schools.

URL• When you complete the document, you

``publish'' the document by delivering it to a computer that runs a Web server program.

• This process involves freedom on your part to assign a name that will be associated with this new document; this name is called the document's Universal Resource Locator(URL) address.

• the URL identifies your document uniquely among all other documents in the world.

URLs

• the URL is a single, universal address mechanism that denotes an information service or document type, the location of the hosting server within the Internet, and the location of that information within the host, and may also actually include information to be forwarded to that server for processing.

• The URL address was immediately embraced by the entire industry as a standard for referencing services as well as data.

.• .

The advantage of using URLs• This is a similar situation to having a post office box;

no matter where you move, your mail can still find its way to you via a simple, unchanging address.

• Virtual path addressing, which is handled by the server, permits flexible movement of content files and directories while keeping the original URL address.

• In fact, material can change host computers or even be distributed among several host computers while URLs can remain unchanged with appropriate configuration of the server. 

Virtual Paths• The path addressing scheme which is allowed is actually a virtual path scheme. What this means is that there need not really be any hierarchy of directories (or folders) in the computer's permanent storage area corresponding to those portrayed by the path name in the URL.

• The software administrator who configures the behavior of the Web server has the opportunity to name and rename parts of the path and to assemble a virtual (i.e., in name only) tree from branches spread out all over the actual permanent memory of the computer.

• This allows Web administrators to present a simple,intuitive, and unchanging form to the information available from their web servers despite the often messy and/or changing forms that real information tends to have in real organizations.

Post script and plug-ins• Postscript was a language developed by the Adobe

corporation to describe exactly how a printer should create a printed copy of that document. Wishing not to waste paper, we sometimes want to see a postscript-described document on our computer screen. Several software applications, called postscript viewers, are available to render a postscript document on our display.

• If we have such a viewer application on our computer, we can configure our Web browser to automatically call the application when encountering a hypertext link to a  postscript-style document.

The success of the WWW• The ability to access remote information instantly and

conveniently; • The potential for every user to be a world wide publisher; • The ability to incorporate formatted text, images and, later,

interactive components, permitting artistic expression. This was important in attracting widespread participation by individuals and by the commercial sector, which found the Web to be a ready-made canvas for high quality advertising;

• Multimedia communications capability all channeled through a single device, your computer;  

• Hyperlinks that enable the user to pursue desired topics immediately without regard to location of the source material;  

• Powerful search capabilities to locate desired information anywhere on the Web; and

• Flexibility and upgrade capability--the fact that different computer architectures running different operating systems can simply display the same information and be upgraded via various plug-ins to deal with new data types.