Uniform Resource Locator(URL)

URL specifies the exact location of a resource on the Internet.By definition URL is supposed to refer to only those addressing schemes currently in common use for accessing Internet resources.
There are three different types of URL's:

Absolute URL Scheme Hyperlink
Anchored Elements Named Anchors Non-text anchors

Absolute URL

Absolute URL's use complete details to give the location of a resource.To accompolish this the transfer Protocol must be specified first,then the particular server on which the file is located,and finally the actual path to the file on the server.

Relative URL

Relative URl's are used for accessing files when the full Internet address is unneccessary.When are accessed,the base part of the URL is automatically concatenated to the relative URL by the browser,so it does'nt have to be explicitly identified.They are also called as Partial URL's.

Fragment URL's

Using anchors it can be referenced in bookmark fashion as a Fragment URL.The anchor could be either <a > tag are the ID attribute of any element.The fragment identifier has scope only within the document its found in.

Absolute URL Scheme Hyperlink
Anchored Elements Named Anchors Non-text anchors

URL Schemes

The most commonly used URL schemes are as follows:

  • HTTP
  • Mail TO
  • NEWS
  • FTP

Most of the URL schemes have optional elements,which are'nt usually specified because most network administrators simply accept the default ports.

Hyper Text Transfer Protocol(HTTP)

HTTP is the web's native protocol.It's used to access HTML pages through web browsers and other client agents.

Mail To

It is used to invoke e-mail programs in the URL.The effect of mailto when invoked is to launch an e-mail program with the to field filled in with the value from email address.

NEWS

A NEWS URL simply provides their news reader software with the parameters to locate a particular news group or even a particular article,if you have the message ID for it.

File Transfer Protocol(FTP)

FTP is still in use for retrieving files from FTP servers.For most FTP sites all you need to supply is the files protocol,host,and the file address,and the software takes care of the rest

Absolute URL Scheme Hyperlink
Anchored Elements Named Anchors Non-text anchors

Hyperlink

Hypertext is the very essence and heart of the WWW.By hyperlinking files are arranged coherently and allows interlocking.
Uses of Hyperlink are:

  • Using anchor element connection to other HTML pages is provided in a particular website or to related topics from other web sites.
  • Images and sounds,can be embedded in a HTML page.
  • Connection to non HTML resources,includig portable documents such as Adobe Acrobat PDF files or video clips such as quick time movies

Hyperlinks are often used so that a website can be broken up into several different HTML pages all of which are linked to eachother.

Structure of Hyperlinks

Every hyperlink has two components:the source anchor and destination anchor.For instance,<a href="http://www.pathfinder.com/">,the destination of the link is the pathfinder website.The source end of the link is whatever HTML document contains this code.All hyperlinks are two way,the source and destination ends are equally available by clicking the back and forward buttons of your web browser.

The Anchor Element

Anchor element is specifed within the body of the HTML page.When used to turn text into a hyperlink,the text is usually coloured blue and underlined.Anchor elements that used to create named anchor points within the document are typically rendered in the same style as the surrounding text.if the anchor contains an image,either with or without accompaying text,the image is usualy outlined in blue.
The Syntax is:

<a [name=msn][href=URL]>Homepage</a>

where msn is an identifier unique to the document and URL is a URL of another network resource.Anchor tags with any attributes can still be assigned href and name values through Scripting.
While creating hyperlink href(hypertext reference)attribute is the only absoulte neccessity.
The minimum required code define a hyperlink:

<a href="'>an empty URL.</a>
Absolute URL Scheme Hyperlink
Anchored Elements Named Anchors Non-text anchors

Named Anchors

Named anchors are those elements that contain either an <a> tag with a name attribute or any element with an assigned ID.Either the name or ID attributes can be used because they are the same.Both name and ID occupy the name space,which means they share the same place in the computers memory within the scope of the HTML document where they are found.
The following is an example:

<h1>Dictionaries</h1>
<p><a href="#Ehglish">English dictionary</a></p>
<p><a href="#Hindi">Hindi dictionary</a></p>
<p><a href="#Tamil">Tamil dictionary</a></p>
<h2 ID="English">English dictionary</h2>
<h2 ID="Hindi">Hindi dictionary</h2>
<h2 ID="Tamil">Tamil dictionary</h2>

The result will be :

Dictionaries


English dictionary


Hindi dictionary


Tamil dictionary


English dictionary


Hindi dictionary


Tamil dictionary

Non-Text Anchors

Images are also used to link.This is done by substituting the textual portion of the link with in an image URL.
The Syntax:

<a href="http://www.puquest.com"><img src="graphics.gif"></a>

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