How would I describe how a browser connects?
Now let’s look at the details of how the browser finds a particular web page.
URLS: ADDRESSES FOR WEB PAGES Before your browser can connect with a website, it needs to know the site’s address, the URL. The URL (Uniform Resource Locator) is a string of characters that points to a specific piece of information anywhere on the web. In other words, the URL is the web- site’s unique address.
panel 2.7
Internet Explorer (top) and Mozilla Firefox (bottom)
Notice the different tool- bar and tool setups.
Survival Tip
Do Home Pages Endure?
The contents of home pages often change. Or they may disappear, and so the con- necting links to them in other web pages become links to nowhere. To find out how to view “dead” pages, go to:
http://web.ticino.com/
multilingual/Search.htm
66
Chapter 2
A URL consists of (1) the web protocol, (2) the domain name or web server name, (3) the directory (or folder) on that server, and (4) the file within that directory (perhaps with an extension such as html or htm ). Consider the fol- lowing example of a URL for a website offered by the National Park Service for Yosemite National Park:
Protocol
Domain name (web server name)
Directory name,
or folder
File (document)
name and extension
http://www.nps.gov/yose/home.htm
Let’s look at these elements.
•
The protocol: http:// As mentioned, a protocol is a set of communicationrules for exchanging information. The web protocol, HTTP, was developed by Tim Berners-Lee, and it appears at the beginning of some web
addresses (as in http://www.mcgraw-hill.com ). It stands for HyperText Transfer Protocol (HTTP) , the communications rules that allow browsers to connect with web servers. (Note: Most browsers assume that all web addresses begin with http://, and so you don’t need to type this part; just start with whatever follows, such as www. )
•
The domain name (web server name): www.nps.gov/A domain issimply a location on the internet, the particular web server. Domain names tell the location and the type of address. Domain-name components are separated by periods (called “dots”). The last part of the domain, called the top-level domain, is a three-letter extension that describes the domain type: . gov, .com, .net, .edu, .org, .mil, .int— government, commercial, network, educational, nonprofit, military, or international organization. In our example, the www stands for “World Wide Web,” of course; the . nps stands for “National Park Service,” and . gov is the top-level domain name indicating that this is a government website.
panel 2.8
Home page
This is a website’s first page, or welcome page.
The Internet & the World Wide Web 67 The meanings of other internet top-level domain abbreviations appear in
the box on the next page. (
•
See Panel 2.9. ) Some top-level domain names also include a two-letter code extension for the country—for example, . us for United States, . ca for Canada, . mx for Mexico, . uk for United Kingdom, . jp for Japan, . in for India, . cn for China. These country codes are optional.•
The directory name: yose/ The directory name is the name on the serverfor the directory, or folder, from which your browser needs to pull the file.
Here it is yose for “Yosemite.” For Yellowstone National Park, it is yell.
•
The file name and extension: home.htm The file is the particular pageor document that you are seeking. Here it is home.htm, because you have gone to the home page, or welcome page, for Yosemite National Park.
The . htm is an extension to the file name, and this extension informs the browser that the file is an HTML file. Let us consider what HTML means.
URLs & EMAIL ADDRESSES: NOT THE SAME A URL, you may have observed, is not the same thing as an email address. The website for the White House (which includes presidential information, history, a tour, and a guide to fed- eral services) is www.whitehouse.gov. Some people might type president@
whitehouse.gov and expect to get a website, but that won’t happen. We explain email addresses in another few pages.
Domain Name Authorized Users Example
.aero air-transport industry [email protected]
.biz businesses [email protected]
.com originally commercial; now any- one can use
[email protected] .coop cooperative associations [email protected] .edu postsecondary accredited
educational and research institutions
.gov U.S. government agencies and bureaus
[email protected] .info generic information service
providers
[email protected] .int organizations established
by international treaties between governments
sectretary_general@unitedna- tions.int
.jobs human resources managers [email protected] .mil U.S. military organizations [email protected] .mobi providers of mobile products and
services
.museum museums [email protected]
.name individuals [email protected]
.net generic networking organizations [email protected] .org generic organizations, often non-
profit and professional (non- commercial)
.post Universal Postal Union* [email protected] .pro credentialed professionals &
related entities
[email protected] tel. For businesses and individuals to
publish their contact data
.travel travel industry [email protected]
.xxx adults-only website [email protected]
Note: The number of domain names is expanding; for a list of current domain names, go to www.
iana.org/gtld/gtld.htm.
*Some groups pay $45,000 or more to ICANN for a particular domain name.
panel 2.9
Internet top-level domain abbreviations and users
68
Chapter 2
panel 2.10
An HTML document and hyperlinks
Using the mouse to click on the hyperlinked (underlined) text con- nects you to another location in the same website or at a different site.