miw chapter 2

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Modeling the Internet and the WebSchool of Information and Computer ScienceUniversity of California, Irvine

Basic WWW Technologies

2.1 Web Documents.

2.2 Resource Identifiers: URI, URL, and URN.

2.3 Protocols.

2.4 Log Files.

2.5 Search Engines.


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What Is the World Wide Web?

The world wide web (web) is a network ofinformation resources. The web relies on threemechanisms to make these resources readilyavailable to the widest possible audience:

1. A uniform naming scheme for locating resourceson the web (e.g., URIs).

2. Protocols, for access to named resources over

the web (e.g., HTTP).3. Hypertext, for easy navigation among resources

(e.g., HTML).


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Internet vs. Web

Internet:

Internet is a more general term

Includes physical aspect of underlying networks

and mechanisms such as email, FTP, HTTPWeb:

Associated with information stored on theInternet

Refers to a broader class of networks, i.e. Webof English Literature

Both Internet and web are networks


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Essential Components of WWW

Resources:

Conceptual mappings to concrete or abstract entities, which do not

change in the short term

ex: ICS website (web pages and other kinds of files)

Resource identifiers (hyperlinks): Strings of characters represent generalized addresses that may

contain instructions for accessing the identified resource

http://www.ics.uci.edu is used to identify the ICS homepage

Transfer protocols: Conventions that regulate the communication between a browser

(web user agent) and a server
http://www.ics.uci.edu/http://www.ics.uci.edu/


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Standard Generalized Markup

Language (SGML)

Based on GML (generalized markup language),

developed by IBM in the 1960s

An international standard (ISO 8879:1986)

defines how descriptive markup should beembedded in a document

Gave birth to the extensible markup language

(XML), W3C recommendation in 1998


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SGML Components

SGML documents have three parts: Declaration: specifies which characters and delimiters

may appear in the application

DTD/ style sheet: defines the syntax of markupconstructs

Document instance: actual text (with the tag) of the

documents

More info could be found:http://www.W3.Org/markup/SGML
http://www.w3.org/markup/SGMLhttp://www.w3.org/markup/SGML


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DTD Example One

ELEMENT is a keyword that introduces a new

element type unordered list (UL)

The two hyphens indicate that both the start tag

and the end tag for this element

type are required

Any text between the two tags is treated as a listitem (LI)


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DTD Example Two

The element type being declared is IMG

The hyphen and the following "O" indicatethat the end tag can be omitted

Together with the content model

"EMPTY", this is strengthened to the rulethat the end tag must be omitted. (no

closing tag)


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HTML Background

HTML was originally developed by Tim Berners-

Lee while at CERN, and popularized by the

Mosaic browser developed at NCSA.

The Web depends on Web page authors andvendors sharing the same conventions for

HTML. This has motivated joint work on

specifications for HTML.

HTML standards are organized by W3C :

http://www.w3.org/MarkUp/
http://www.w3.org/MarkUp/http://www.w3.org/MarkUp/


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HTML Functionalities

HTML gives authors the means to:

Publish online documents with headings, text, tables,

lists, photos, etc

Include spread-sheets, video clips, sound clips, and otherapplications directly in their documents

Link information via hypertext links, at the click of a

button

Design forms for conducting transactions with remote

services, for use in searching for information, making

reservations, ordering products, etc


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HTML Versions

HTML 4.01 is a revision of the HTML 4.0 Recommendation first

released on 18th December 1997.

HTML 4.01 Specification:

http://www.w3.org/TR/1999/REC-html401-19991224/html40.txt

HTML 4.0 was first released as a W3C Recommendation on 18December 1997

HTML 3.2 was W3C's first Recommendation for HTML which

represented the consensus on HTML features for 1996

HTML 2.0 (RFC 1866) was developed by the IETF's HTML

Working Group, which set the standard for core HTMLfeatures based upon current practice in 1994.
http://www.w3.org/TR/1999/REC-html401-19991224/html40.txthttp://www.rfc-editor.org/rfc/rfc1866.txthttp://www.rfc-editor.org/rfc/rfc1866.txthttp://www.w3.org/TR/1999/REC-html401-19991224/html40.txthttp://www.w3.org/TR/1999/REC-html401-19991224/html40.txthttp://www.w3.org/TR/1999/REC-html401-19991224/html40.txthttp://www.w3.org/TR/1999/REC-html401-19991224/html40.txthttp://www.w3.org/TR/1999/REC-html401-19991224/html40.txt


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Sample Webpage


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Sample Webpage HTML

Structure

The title of the webpage

Body of the webpage


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HTML Structure

An HTML document is divided into a head section

(here, between and ) and a body

(here, between and )

The title of the document appears in the head (alongwith other information about the document)

The content of the document appears in the body. The

body in this example contains just one paragraph,

marked up with


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Resource Identifiers

URI: Uniform Resource Identifiers

URL: Uniform Resource Locators

URN: Uniform Resource Names


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Introduction to URIs

Every resource available on the Web has anaddress that may be encoded by a URI

URIs typically consist of three pieces:

The naming scheme of the mechanism usedto access the resource. (HTTP, FTP)

The name of the machine hosting the

resource The name of the resource itself, given as a

path


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URI Example

http://www.w3.org/TR

There is a document available via the HTTP

protocol

Residing on the machines hosting

www.w3.org

Accessible via the path "/TR"
http://www.w3.org/TRhttp://www.w3.org/http://www.w3.org/http://www.w3.org/TR


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Protocols

Describe how messages are encoded and

exchanged

Different Layering Architectures

ISO OSI 7-Layer Architecture

TCP/IP 4-Layer Architecture


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ISO OSI Layering Architecture


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ISOs Design Principles

A layer should be created where a different levelof abstraction is needed

Each layer should perform a well-defined

function The layer boundaries should be chosen tominimize information flow across the interfaces

The number of layers should be large enough

that distinct functions need not be throwntogether in the same layer, and small enoughthat the architecture does not become unwieldy


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TCP/IP Layering Architecture


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TCP/IP Layering Architecture

A simplified model, provides the end-to-

end reliable connection

The network layer

Hosts drop packages into this layer, layer

routes towards destination

Only promise Try my best

The transport layer

Reliable byte-oriented stream


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Hypertext Transfer Protocol (HTTP)

A connection-oriented protocol (TCP) used

to carry WWW traffic between a browser

and a server

One of the transport layer protocol

supported by Internet

HTTP communication is established via a

TCP connection and server port 80


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GET Method in HTTP


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Domain Name System

DNS (domain name service): mapping fromdomain names to IP address

IPv4:

IPv4 was initially deployed January 1st

. 1983 andis still the most commonly used version.

32 bit address, a string of 4 decimal numbersseparated by dot, range from 0.0.0.0 to

255.255.255.255.IPv6:

Revision of IPv4 with 128 bit address


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Top Level Domains (TLD)

Top level domain names, .com, .edu, .gov and ISO

3166 country codes

There are three types of top-level domains:

Generic domains were created for use by the Internetpublic

Country code domains were created to be used by

individual country

The .arpa domain Address and Routing ParameterAreadomain is designated to be used exclusively for Internet-

infrastructure purposes
http://www.iana.org/gtld/gtld.htmhttp://www.iana.org/cctldhttp://www.iana.org/arpa-dom/http://www.iana.org/arpa-dom/http://www.iana.org/cctldhttp://www.iana.org/gtld/gtld.htm


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Registrars

Domain names ending with .aero, .biz,

.com, .coop, .info, .museum, .name, .net,

.org, or .pro can be registered through

many different companies (known as"registrars") that compete with one another

InterNIC at http://internic.net

Registrars Directory:

http://www.internic.net/regist.html
http://internic.net/http://www.internic.net/regist.htmlhttp://www.internic.net/regist.htmlhttp://internic.net/


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Server Log Files

Server Transfer Log: transactions between a

browser and server are logged

IP address, the time of the request

Method of the request (GET, HEAD, POST) Status code, a response from the server

Size in byte of the transaction

Referrer Log: where the request originated

Agent Log: browser software making the request (spider)

Error Log: request resulted in errors (404)


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Server Log Analysis

Most and least visited web pages

Entry and exit pages

Referrals from other sites or searchengines

What are the searched keywords

How many clicks/page views a pagereceived

Error reports, like broken links


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Server Log Analysis


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Modeling the Internet and the WebSchool of Information and Computer Science 32

Search Engines

According to Pew Internet Project Report

(2002), search engines are the most popular

way to locate information online

About 33 million U.S. Internet users query on

search engines on a typical day.

More than 80% have used search engines

Search Engines are measured by coverage and

recency
http://www.pewinternet.org/reports/pdfs/PIP_Search_Engine_Data.pdfhttp://www.pewinternet.org/reports/pdfs/PIP_Search_Engine_Data.pdf