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The architecture of the web today is largely founded on Tim Berners-Lee's original design. Thanks also to Berners-Lee's follow-on efforts with the W3C.The following subsections provide more information:
Addresses - Different types of URL's.
Servers - The programs that send web pages to browsers.
HTTP - The protocol servers use to communicate web pages.
Pages - Web pages are windows with links.
HTML - The language used to describe web pages.
Links - The interconnections in hypertext.
Java & JavaScript - Adding programs to web pages.
Addresses
Uniform Resource Locators (URL),the syntax and semantics of formalized information for location and access of resources via the Internet. Please go througth it for details of URL
Servers
The architecture involves two programs, a client 'browser'' and a server, communicating across a network... The server is free to generate the documents either by sending real files, or by generating virtual hypertext on the fly in response to a request.
Each web site is managed by a web server.A web server for a web site handles all of the network communications with individual user browsers. The server accepts HTTP requests for web pages, and sends the pages to the browser over the net.
Any Windows, Macintosh, or Unix computer is capable of running a web server when it is connected to the net. However, it isn't practical over a dial-up connection since they are slow, not always connected, and change their IP Address every time you log on. A dedicated connection in an office, or a high speed home connection like DSL, provides the always-on attribute needed to run a reliable web server.
Different web servers have different scalability, robustness, security, transportability, and related features. A web server may be dedicated for one domain, or maintain web sites for several domains.
HTTP
The HTTP client sends a document identifier with or without search words, and the server responds with hypertext or plain text. The protocol runs over TCP, using one connection per document request. The browser acts as a pipeline, so that as the bytes arrive from the server they can be presented to the reader as soon as they arrive.
The Hypertext Transfer Protocol (HTTP) is used when your browser connects to a web server, requests a web page from the server, and downloads the page. It is the common standard that enables any browser to connect to any server, anywhere in the world.
HTTP was originally designed by Tim Berners-Lee to support the special demands of web communications, with an emphasis on efficiency, and an original target page load time of under a tenth of a second (given a fast enough network). Modern HTTP
Your browser can open more than one HTTP connection at once to download different parts of a web page, downloading the text, graphics, and other objects on the page in different orders. That is why you may see the status messages in the bottom of your browser window switch between a message like "downloading 62% of 15K" to "downloading 38% of 47K" on the same page -- there are different HTTP connections.
Some browsers enable you to specify the download priorities so that, for example, graphics are not loaded, text is loaded before graphics, everything is loaded at once, etc. Check your individual browser preferences.
The HTTP protocol is standardized by the W3C
Consortium, which manages the standard development and enhancement.
Pages
A web page is displayed in a normal computer application window, and looks not unlike a word processing document window. Scroll bars are displayed if the page is too long or too wide, and you can perform the usual windowing functions such as minimize, maximize, change size, and close.
A web page has a similar format to a magazine page, consisting of text and graphics in a functional layout. Once created and published on a web site, the web page is communicated to web browsers by a web server.
Graphics are displayed if your browser supports them and they haven't been turned off in your configuration settings to optimize the download speed. With most browsers you can right-click on the image and select "View Image" to view it by itself, or "Save Image As" to save the image file to your computer for later viewing with another application. Graphics come in a wide range of formats. At one time GIF's were the most popular, but lately they are going out of style.
Web pages have been published on almost every
subject under the sun, by almost every type of person and organization. There
are a wide range of applications that enable the construction of web pages in
the HTML language, and most word processors now let you save documents in HTML
format.
You can sometimes tell from the name of the page whether it is an organization
or a personal home page, because individual's home pages sometimes include "~"
or "^", as in:
http://www.twenty.net/~jsmith/home.html
After you navigate through several web pages,
you can click on the Back button on your browser to go back to a previous page,
and Forward to go forward again (see surfing).
HTML
In 1966... I knew nothing about computers, but I knew there had to be a better way to produce documents than dictating them, reviewing a draft, marking up the draft with corrections, reviewing the retyped draft, and then, in frustration, seeing that the typist had introduced more errors while making the corrections...
HTML is the simple and powerful language used to describe web pages. In 1969, the same year the ARPANET was created, Charles Goldfarb, Edward Mosher, and Raymond Loriewas invented the Generalized Markup Language (GML) to facilitate text management in large information systems. GML was based on the work of Rice and Tunnicliffe with tagging schemes, and added a formal document structure, so that any computer program could automatically process and format the individual parts of the document.
In 1980, the American National Standards Institute (ANSI) committee built on GML and published a working draft of Standard GML, or SGML. Major adopters of the standard included the US Internal Revenue Service and Department of Defense. A draft international standard was adopted by the European Community in 1985, and a final standard was published as ISO 8879:1986. The final standard was published with a working SGML system developed by Anders Berglund, then of the European Particle Physics Laboratory (CERN).
A few years later another scientist at CERN, Tim Berners-Lee, invented the HyperText Markup Language (HTML) to define the structure of web pages. Tim never planned HTML to be more than a structure into which a wide range of multi-media documents would be fitted, but it was designed well enough that it came to be used to present a wide range of content itself.
The main structure of modern HTML was agreed at a meeting at the first WWW conference held the week of 25 May, 1994, including incorporation of tables, graphics, and mathematics symbols.
HTML is designed to be as simple as possible. Each command consists of an opening tag, and a closing tag with an added "/". Some of the most common HTML commands are listed below, together with the result displayed when the HTML is read by a web browser.
e.g if we write HTML code "The water is
<b>very</b> blue " .The Web Page Result will be "The water
is very blue"
Every web page is written in HTML. The language is text based, so it's easily and quickly communicated across the net. You can view the HTML for any web page you visit (including this one) by selecting the menu item "View / Source" on most web browsers. When you are finished viewing the web page source you can safely close that window without affecting any of the pages you are viewing.
Dan Connolly, Jon Bosak, and others at the W3C have also developed a successor to SGML called the Extensible Markup Language (XML), which provides the structure to enable design of a range of languages like HTML for various purposes.
You can copy the HTML source from a web page to learn from it, but you should not copy someone else's unique work in your own web site without getting their permission and giving them credit on your site.
Other technologies used to dynamically create web pages on the server often give their pages a different three-letter extension, although the final page served up to the browser is still constructed in HTML:
Links
Links are used to connect web pages. The key feature of the web page is the hypertext link, first popularized by Ted Nelson, and used by Douglas Engelbart and Tim Berners-Lee.
A link is a piece of text or graphic that transfers you to another web page when you click on it. The standard link is blue and underlined like this. Links to other pages within the LivingInternet.com site are specially designated in italics. Graphics that contain embedded links sometimes have a blue border.
When you click on a link it is recorded in your history file, and then usually changes to a darker blue so you can tell later if you've already visited it.
When your cursor passes over a link, most browsers display the URL of the linked page is shown on the bottom border of the window. Sometimes you can tell just from the URL whether or not you want to visit the link.
Navigation of links through pages is called surfing. A link can be to another section of the same page, to another page on the same web site, or to another web page somewhere else in the world. When you jump to a new page, you can continue from there, go back to the page you came from, or click on another link to jump to a new location.
The cursor will turn into a hand when you pass it over a graphic containing links. Some pictures contain more than one link, and the x-y position coordinates of the cursor in the graphic may be displayed on the bottom window border, which the web site uses to determine which link in the graphic to select.
Sometimes when you click on a link it opens a
new window. You can deliberately open any page in a new window by right-clicking
on it and selecting "Open in new window". You can close or minimize
a new page and return to the first page whenever you wish.
Java & JavaScript
Applets extend the capabilities of a web page on-the-fly. Web pages consist of more than text and graphics -- they also often contain a range of programs that scroll text, display graphics, calculate results, and perform other actions. These programs are written in text-based computer languages, so they are downloaded very quickly, and are sometimes called "applets" as a diminutive of "applications". The most common applets are Java programs and JavaScript / ECMAScript scripts.
These programs are written in compact, text-based computer languages, so they take up little bandwidth and are downloaded very quickly, making them ideal for adding sophisticated custom functionality to a web page that may be accessed over low bandwidth connections.
JavaScript programs are usually embedded in the page when it is downloaded. This site LivingInternet.com is run by JavaScript programs -- you can view some of the code by selecting "View / Source" from your browser menu. Java programs may be downloaded with the page, or downloaded quickly when the user performs an action that requires one.
Applets run on a software engine in your web browser or on your computer called a "virtual machine". Most web browsers include a virtual machine for JavaScript, and most operating systems include a virtual machine for Java.
You can sometimes tell when an applet is running when a message is displayed in the browser border saying something like: "Applet ThisApplet running".
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