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UNIFORM RESOURCE LOCATOR
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There were three question that had to be answered before a selected page could be displayed:
1. What is the page called?
2. Where is the page located?
3. How can the page be accessed?
Each page is assigned a URL (Uniform Resource Locator) that effectively serves as the page’s worldwide name.
URL is like a sign pointing to something on the internet service tell that what type of internet service to use.
URL have three part:
how_to_get_there://where_to_go/what_to _get the protocol The DNS name of the host Local name uniquely indicating the specific page
For example…
http://www.cs.vu.nl/welcome.html
protocol is http
DNS name of the host www.cs.vu.nl
file name is welcome.html
URL scheme is open-ended in the sense that it is straight forward to have protocol other than HTTP
Name Used for Examplehttp Hypertext http://www.cs.vu.nl/ast/
ftp FTP ftp://ftp.cs.vu.nl/pub/minix/README
File Local file /user/suzanne/prog.c
News News group News:comp.os.minix
Gopher Gopher Gopher://gopher.tc.umn.edu/11/libraries
mailto Sending email mailto
telnet Remote login telnet://www.w3.org:80
LOCATING INFORMATION IN WEB The web contain wast amout of
information,finding the right item is not so easy.
Programs that search the web are sometimes called search engines,spiders,crawlers,worms,orknowbots.
pointer to URLS
Pointers to title String
storage
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21 44
Hash code
Overflow chains
url_table heap Hash table
HTML
What it is…
HTML is an application of ISO standard 8879,specialized to hypertext and adapted to the web.
Very structured markup language for building web pages.
A markup language is a collection of elements, which are used to indicate structure and format of a document
Browser simply has to understand the markup commands
HTML standards
When Mosaic was the only browser, the language it interpreted,HTML 1.0,was the de facto standard.
When new browser came along, there was a need for a formal standard, so HTML2.0 standard was produced.
HTML3.0 was initially created as a reserch effort to add many features to HTML2.0,including tables,toolbars,mathematical formulas, advanced stylesheets,and more
A complete html element is defined by a start tag, an end tag, possible attributes and a content model
The commands inside the tags are called directives
A proper web page consists of a head and a body enclosed by <HTML>and</HTML> tag.
Common HTML tags Tag Description
<HTML>…</HTML> Declares the web page to be written in HTML
<HEAD>…</HEAD> Delimits the page’s head
<title>…</title> Defines the title
<body>…</body> Delimits the page’s body
<Hn>…</Hn> Delimits a level n heading
<B>…</B> Set…in boldface
<l>…</l> Set…in italics
<UL>…</UL> Brackets an unordered
<OL>…</OL> Brackets a numbered list
<MENU>…</MENU> Brackets a menu of<LI>items
Tag Description
<LI> Start of a list item
<BR> Force a break here
<p> Start of paragraph
<HR> Horizontal rule
<PRE>…</PRE> Preformatted text; do not reformat
<IMG SRC=“ ...”> Load an image here
<A HRFE=“…”>…</A> Define a hyper link
Forms
Forms contain boxes or buttons that allow users to fill in information or make choices and then send the information back to the page’s owner.
Using the <INPUT> tag for this purpose. Most common forms are blank fields for
accepting user text, boxes that can be checked, active maps, and submit buttons.
Thank you
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