net 1

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Network (internet) applications

• WWW
• Client-server
• Semantic Web
• (Client server side processing)

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World Wide Web
Internet
Web server
Borg
Public_html
Index.html

• Parts of the puzzle
• URL
• HTTP
• HTML

Web browser
Your Machine
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HTTP Hyper Text Transfer Protocol

• Lightweight protocol that browsers and servers
  use to communicate with one another
• On top of (in the application layer of) the
  TCP/IP model
• HTTP session begins when a clients browser
  requests a Web page. Once the server responds by
  sending the page requested, the HTTP session ends

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GET /index.html HTTP/1.1User-Agent
Lynx/2.4Connection Keep-AliveHost
www.openaccess.comAccept text/html
client request
Server response
HTTP/1.1 200 OKDate Thu, 22 July 1998 184055
GMTServer Apache 1.3.5 (Unix)
PHP/3.0.6Last-Modified Mon, 19 July 1997
160322 GMTContent-Type text/htmlContent-Lengt
h 12987...
MIME type (Multipurpose Internet Mail Extension)
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HTTP is stateless!!!

• stateless because every request that a browser
  makes opens a new connection that is immediately
  closed after the document is returned
• even a web page with many objects (graphics,
  sound, video, etc) requires separate HTTP
  requests for each object
• each operation is unaware of any other connection
• the server cannot maintain state information
  about successive requests easily

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Client-Server Model
Not mainframe-terminal, not necessarily big vs.
small (rather specialized)
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Type of servers

• Database servers
• Web servers
• Mail servers
• Print Servers
• Object servers
• Groupware servers
• etc

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A three-tier architecture
What is middleware?
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Peer-to-peer vs. Client-Server

• The new hype
• Uniform role of all nodes
• Direct communication
• Decentralized control
• Scalable

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Web client-server

• Web client (browser) an application program that
  runs on a client computer and requests and
  displays web pages
• can also support other features such as email and
  newsgroups
• Web server a server-side application program
  that runs on a host computer and responds to
  requests for web pages

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Commercial Web browsers

• Statistics from August 20021
• Internet Explorer (96)
• Netscape Navigator (3.4)
• Other browsers (0.6)
• Opera fastest browser
• NeoPlanet - customizable, including skins
• How has IE become such a dominant player in the
  browser market?

1Source http//www.statmarket.com/cgi-bin/sm.cgi?
smfeatureweek_stat retrieved Sept. 15, 2002.
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Web client/server communication

• Like any other client/server application, web
  browsers and servers need a way to
• Locate each other so they can send requests and
  responses back and forth
• Uniform Resource Locator (URL)
• Communicate with one another
• Hypertext Transport Protocols (HTTP)
• (See networking section)

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(X)HTML

• Hypertext Markup Language
• presentation language
• embedded text that tells the clients browser how
  to display the page elements
• standard formatting language that all browsers
  understand
• theoretically !
• example tag
• lth1gt ECMM 6000 lt/h1gt

ECMM 6000
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Interactivity

• HTML is a presentation language not a
  programming language
• controls the appearance of the information on the
  clients screen but does not support processing
  or manipulating information
• early web browsers were limited to displaying
  static pages
• But many business applications require
  interactivity ? Client-side server-side
  processing

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Thin vs. Fat Clients

• where the processing takes place
• Early browsers were thin clients primary
  function was to display web documents containing
  text and simple graphics
• Todays browsers are not thin, they provide a
  great deal of functionality and processing on the
  client side
• Scripting, active object support, email, web page
  authoring, audio, streaming media, Instant
  messaging

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• Web Hub
• Content Management Console

Google News
Admin
XML Content Repository
Retrieve
General Public
Modify
Control Panel
Front End Site
P u b l i c
Modify
Database
Members Section
Alumni
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TML (XML)
ltthomasgt ltlecture typeearlygt ltopeninggt Gu
ten Morgen lt/openinggt ltmessagegt bla
bla lt/messagegt ltlecturegt ltresearchgt ltpapergt
lt/papergt lt/researchgt lt/thomasgt
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DTD
lt!ELEMENT ele_name (list of child elements
?)gt Leaf element lt!ELEMENT name
(PCDATA)gt lt!ATTLIST ele_name att_name
att_type att_valuegt lt!ENTITY ent_name
ent_valuegt
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DTD
XML Document
XML Parser Syntax Validator
valid / not valid
DTD Document
For example MSXML
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XSLT
XML Document
XSLT Processor
XSL Document
XSLT Document
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XSLT
Include in XML document lt?xml-stylesheet
typetext/xsl hrefURL ?gt XSLT
document ltxslstylesheet version 1.0
xmlnsxsl url of xslt xmlns url of
xhtmlgt ltxsltemplates match rootgt
lthtmlgt ltheadgt lt/headgt ltbodygt lth1gt
.. ltxslfor-each select taggt
ltspan style whatevergt message lt/spangt
ltxslvalue-of select subtag /gt
ltother html tagsgt . lt/xslfor-eachgt lt/html
gt lt/xsltemplategt lt/xslstylesheetgt
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Tim Berners-Lee
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Web service architecture
http//www.w3.org/2002/ws/
Adopted from Clabby, 2002
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SOAP

• Simple Object Access Protocol
• XML-based protocol
• Exchange of information between applications over
  HTTP
• Seems to become the widely accepted solution to
  electronic data interchange (EDI) and remote
  procedure call (RPC, CORBA, etc)

http//www.w3.org/TR/soap12-part0/
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Latest Web Service Architecture (W3C, 2004)
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From http//www.w3.org/2001/sw/
Semantic Web The Semantic Web provides a common
framework that allows data to be shared and
reused across application, enterprise, and
community boundaries. It is a collaborative
effort led by W3C with participation from a large
number of researchers and industrial partners. It
is based on the Resource Description Framework
(RDF), which integrates a variety of applications
using XML for syntax and URIs for naming. "The
Semantic Web is an extension of the current web
in which information is given well-defined
meaning, better enabling computers and people to
work in cooperation." -- Tim Berners-Lee, James
Hendler, Ora Lassila, The Semantic Web,
Scientific American, May 2001
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RDF (Web) Resource Description Framework
Create meaning for automated processing
intelligent agents
http//www.w3.org/TR/rdf-primer/
Web Ontology OWL
http//www.w3.org/TR/owl-features/
Standardized Query Language SPARQL
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Web Ontology OWL
http//www.w3.org/TR/owl-features/