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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

0

1

2

3

20

1

2

3

4

5 19 6

21 44

Hash code

Overflow chains

url_table heap Hash table

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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