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Web 2.1 and Rich Internet Applications Introduction


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Title: Web 2.1 and Rich Internet Applications Introduction

Web 2.1 and Rich Internet ApplicationsIntroductio
  • Dr Suthikshn Kumar

Course Content
  • Background
  • Client Side Technologies
  • Overview of XML
  • Web Services
  • Building Rich Internet Applications with AJAX
  • Building Rich Internet Applications with Flex-1
  • Flex-II
  • Building Advanced Web 2.0 Applications

  • What is Web 2.0?
  • Folsonomies and Web 2.0
  • Software as a Service ( SaaS) and Web 2.0
  • Convergence
  • Iterative Development
  • Rich User Experience
  • Multiple Delivery Channels
  • Social Networking
  • ( 3 hours)

Client Side Technologies
  • Web browsers and Web Servers
  • URL, MIME, HTTP, XHTML, Plugins and Filters
  • CSS
  • Javascripts, General Syntactic characteristics,
    primitives, operations and Expressions, Control
    statements, Simple Examples
  • DOM, Events and Event handling, DOM2 event model
  • ( 6 Hours)

  • Basics, syntax,
  • XML Schemas
  • Document Type Definitions
  • Displaying XML Documents
  • XML Parsors
  • ( 3 Hours)

Web services
  • SOAP
  • RPC Style SOAP
  • Document style SOAP
  • WSDL
  • REST Services
  • JSON Format
  • JSON syntax
  • JSON versus XML
  • ( 4 hours)

  • AJAX Principles
  • Technologies behind AJAX
  • Dynamic web applications through Hidden frames
    for both GET and POST methods
  • IFrames
  • Asynchronous communication and AJAX application
  • XMLHTTP Object
  • Cache control
  • AJAX Patterns Predictive fetch patterns,
    submission throttling pattern, periodic refresh,
    multi stage download, fall back patterns
  • ( 10 Hours)

Flex-I and Flex-II
  • Flash player
  • Flex Framework
  • MXML and ActionScript
  • Flex and Flash Authoring
  • Actionscript 3.0
  • Language Syntax Objects, classes, packages and
    namespaces, operators, functions, conditional and
    looping, classes, interfaces, inheritance
  • Working with XML
  • ( 18 Hours)

Advanced Web 2.0 Applications
  • Definition of mashup applications
  • Mashup techniques
  • Building a simple mashup application with AJAX
  • Remote data communication
  • Strategies for data communication
  • Simple HTTP Services
  • URL loaded in Flex
  • Example Building an RSS reader with AJAX,
    Building an RSS reader with Flex
  • ( 8 Hours)

Text Books
  • Programming the World Wide Web, by Robert
    Sebesta, ( Chapters 1-5, Chap 8), 3rd Edition
  • Professional AJAX, Nicholas C Zakas, ( Chap 1-3,
    Chap 6, Chap 7)
  • Programming Flex 2, Chafic Kazoun, ( Chap 1, 3-7,
    12, 16)
  • Amazon.com Mashups, Francis Shanahan, ( Chap 1
    and Chap 6)

Reference Books
  • Web enabled Commercial Application using HTML,
    DHTML, Javascript, Perl, CGI, Ivan Bayross
  • Essential Actionscript 3.0, Colin Moock
  • Ajax Bible, Steven Holzner
  • A Web 2.0 Primer Pragmatic Ajax, Justin Gehland

Impact of World Wide Web
  • Origin
  • History of Computers, Evolution from Dynosaurs to
    human analogy
  • Tim Berners Lee, 1990
  • W3C
  • Sun Microsystems and Java
  • Open Source, Commercial Software
  • Standards
  • Dot Com burst

Famous websites
  • Google
  • Amazon
  • CNN
  • Wikipedia
  • YouTube
  • Facebook
  • Hotmail, Yahoo
  • Napster
  • Auction

Uses of Web
  • News
  • Email
  • Photo, video, audio, Maps
  • Online Shopping
  • Online Banking
  • Online Education and Examination
  • Searching
  • Collaboration
  • Information
  • Games
  • Medical and Health
  • Applications Calender, Accounting, etc

What is Web 2.0 ?
  • What is Web 1.0?
  • Before 2000
  • Website were well insulated entities that
    executed entirely within the browser and well
    within their own sphere of influence.
  • Users were important but no one would dare
    venture so far as to suggest that users specify
    what they wanted.
  • After 2000
  • Web 2.0 like art, has no real definition.

  • The term folksonomy refers to the process whereby
    a group of people collaborate to organize
    information using an impromptu vocabulary.
  • A common example in the corporate world is team
    building excercises, whereby a group of
    individuals rearrange flash cards on the floor or
    stickers on a white board. By getting a large
    group of peoples input, you have a higher
    probability of getting an appropriate
    classification of the information in question.

How do Folksonomies apply to web 2.0?
  • In the web 2.0, there is a huge amount of
    information and its updated constantly.
  • It would be naïve to think that any one company
    could categorize that information so accurately
    that classification would make sense to everyone.
  • Who better to categorize data than the people
    closest to it?
  • For example Amazon allows users to tag products
    with key words. Over time, this will evolve into
    its own folksonomy where the users are adding
    value for other users simply by using amazon

Software as a Service
  • Web 2.0 is about exposing a rich functionality
    set and much more data.
  • The data is generally accessible to both humans
    and machines, leading to more automation and
    derived applications than ever before.
  • The Web 2.0 world, companies are seeing more and
    more value in offering functionality in reusable
    and interoperable channels such as web services.
  • These channels are then handed over to the user
    for them to do with as they see fit.
  • Web 2.0 puts more trust in the user than ever

  • Data is the King
  • Convergence
  • Iterative Development
  • Rich Browser Experience
  • Multiple Delivery channels
  • Social Networking
  • Rise of the Individual Developer
  • Amazon and Web 2.0

Network applications some jargon
  • user agent interfaces with user above and
    network below.
  • implements user interface application-level
  • Web browser
  • E-mail mail reader
  • streaming audio/video media player
  • Process program running within a host.
  • within same host, two processes communicate using
    interprocess communication (defined by OS).
  • processes running in different hosts communicate
    with an application-layer protocol

Applications and application-layer protocols
  • Application communicating, distributed processes
  • e.g., e-mail, Web, P2P file sharing, instant
  • running in end systems (hosts)
  • exchange messages to implement application
  • Application-layer protocols
  • one piece of an app
  • define messages exchanged by apps and actions
  • use communication services provided by lower
    layer protocols (TCP, UDP)

App-layer protocol defines
  • Public-domain protocols
  • defined in RFCs
  • allows for interoperability
  • eg, HTTP, SMTP
  • Proprietary protocols
  • eg, KaZaA
  • Types of messages exchanged, eg, request
    response messages
  • Syntax of message types what fields in messages
    how fields are delineated
  • Semantics of the fields, ie, meaning of
    information in fields
  • Rules for when and how processes send respond
    to messages

Client-server paradigm
  • Typical network app has two pieces client and
  • Client
  • initiates contact with server (speaks first)
  • typically requests service from server,
  • Web client implemented in browser e-mail in
    mail reader
  • Server
  • provides requested service to client
  • e.g., Web server sends requested Web page,
    mail server delivers e-mail

Processes communicating across network
  • process sends/receives messages to/from its
  • socket analogous to door
  • sending process shoves message out door
  • sending process assumes transport infrastructure
    on other side of door which brings message to
    socket at receiving process

controlled by app developer
controlled by OS
  • API (1) choice of transport protocol (2)
    ability to fix a few parameters (lots more on
    this later)

Addressing processes
  • For a process to receive messages, it must have
    an identifier
  • Every host has a unique 32-bit IP address
  • Q does the IP address of the host on which the
    process runs suffice for identifying the process?
  • Answer No, many processes can be running on same
  • Identifier includes both the IP address and port
    numbers associated with the process on the host.
  • Example port numbers
  • HTTP server 80
  • Mail server 25
  • More on this later

What transport service does an app need?
  • Data loss
  • some apps (e.g., audio) can tolerate some loss
  • other apps (e.g., file transfer, telnet) require
    100 reliable data transfer
  • Bandwidth
  • some apps (e.g., multimedia) require minimum
    amount of bandwidth to be effective
  • other apps (elastic apps) make use of whatever
    bandwidth they get
  • Timing
  • some apps (e.g., Internet telephony, interactive
    games) require low delay to be effective

Transport service requirements of common apps
Time Sensitive no no no yes, 100s msec yes,
few secs yes, 100s msec yes and no
Application file transfer e-mail Web
documents real-time audio/video stored
audio/video interactive games instant messaging
Bandwidth elastic elastic elastic audio
5kbps-1Mbps video10kbps-5Mbps same as above few
kbps up elastic
Data loss no loss no loss no loss loss-tolerant
loss-tolerant loss-tolerant no loss
Internet transport protocols services
  • TCP service
  • connection-oriented setup required between
    client and server processes
  • reliable transport between sending and receiving
  • flow control sender wont overwhelm receiver
  • congestion control throttle sender when network
  • does not provide timing, minimum bandwidth
  • UDP service
  • unreliable data transfer between sending and
    receiving process
  • does not provide connection setup, reliability,
    flow control, congestion control, timing, or
    bandwidth guarantee
  • Q why bother? Why is there a UDP?

Internet apps application, transport protocols
Application layer protocol SMTP RFC
2821 Telnet RFC 854 HTTP RFC 2616 FTP RFC
959 proprietary (e.g. RealNetworks) proprietary (
e.g., Dialpad)
Underlying transport protocol TCP TCP TCP TCP TCP
or UDP typically UDP
Application e-mail remote terminal access Web
file transfer streaming multimedia Internet
Domain Name System
  • Sending email to Ip address such as
    tana_at_128.111.24.41 complicates the matter
  • Every time tana changes her machine, her email id
    has to change
  • Numbers complicate the matter
  • Hence ASCII names were introduced i.e.,
  • Since network only understands the numerical
    addresses, DNS was introduced to convert ASCII
    strings to network addresses.

  • In early days of ARPANET, there was simply a
    file, hosts.txt, that listed all the hosts and IP
    addresses. For a network of few hundred machines,
    this approach worked very well.
  • However, when thousands of PCs and computers were
    connected to net, a new approach was needed.
  • The DNS was invented to solve this problem
  • DNS is a hierarchical, domain based naming scheme
    and a distributed database system.
  • DNS is used for mapping host names and email
    destinations to IP addresses.

DNS Domain Name System
  • . The DNS Name Space
  • . Resource Records
  • . Name Servers
  • Domain Name System
  • distributed database implemented in hierarchy of
    many name servers
  • application-layer protocol host, routers, name
    servers to communicate to resolve names
    (address/name translation)
  • note core Internet function, implemented as
    application-layer protocol
  • complexity at networks edge
  • People many identifiers
  • SSN, name, passport
  • Internet hosts, routers
  • IP address (32 bit) - used for addressing
  • name, e.g., gaia.cs.umass.edu - used by humans
  • Q map between IP addresses and name ?

DNS Name Space
  • Managing a large and constantly changing set of
    names is a nontrivial task.
  • In postal system, name management is done by
    requiring letters to specify country, state,
    city, street address, house number.
  • Thus there is no confusion between Marvin
    anderson on Main st. in white palms in NY and
    Marvin Anderson on Main St. in Austin Texas.
  • DNS works the same way.

The DNS Name Space
  • The internet is divided into over 200 top level
  • Each domain covers many hosts.
  • Each domain is partitioned into sub domains and
    these are further partitioned etc.
  • A portion of the Internet domain name space.

DNS name servers
  • no server has all name-to-IP address mappings
  • local name servers
  • each ISP, company has local (default) name server
  • host DNS query first goes to local name server
  • authoritative name server
  • for a host stores that hosts IP address, name
  • can perform name/address translation for that
    hosts name
  • Why not centralize DNS?
  • single point of failure
  • traffic volume
  • distant centralized database
  • maintenance
  • doesnt scale!

DNS Root name servers
  • contacted by local name server that can not
    resolve name
  • root name server
  • contacts authoritative name server if name
    mapping not known
  • gets mapping
  • returns mapping to local name server

13 root name servers worldwide
Name Servers
  • Part of the DNS name space showing the division
    into zones.

Name Servers (2)
  • Resolver on flits.cs.vu.nl wants to know the IP
    address of the host linda.cs.yale.edu
  • How a resolver looks up a remote name in eight
  • Step1 flits.cs.vu.nl sends query to local name
    server cs.vu.nl
  • Step2 Local name server sends a UDP packet to
    the server edu-server.net
  • Step3 edu-server.net queries the name server
  • Step4 yale.edu forwards the request to
    cs.yale.edu which has the authoritative resource
  • Step5-8 The resource record requested works its
    way back
  • This query method is also known as Recursive

Simple DNS example
root name server
  • host surf.eurecom.fr wants IP address of
  • 1. contacts its local DNS server, dns.eurecom.fr
  • 2. dns.eurecom.fr contacts root name server, if
  • 3. root name server contacts authoritative name
    server, dns.umass.edu, if necessary

authorititive name server dns.umass.edu
requesting host surf.eurecom.fr
DNS example
root name server
  • Root name server
  • may not know authoritative name server
  • may know intermediate name server who to contact
    to find authoritative name server

authoritative name server dns.cs.umass.edu
requesting host surf.eurecom.fr
DNS iterated queries
root name server
  • recursive query
  • puts burden of name resolution on contacted name
  • heavy load?
  • iterated query
  • contacted server replies with name of server to
  • I dont know this name, but ask this server

iterated query
authoritative name server dns.cs.umass.edu
requesting host surf.eurecom.fr
DNS caching and updating records
  • once (any) name server learns mapping, it caches
  • cache entries timeout (disappear) after some time
  • update/notify mechanisms under design by IETF
  • RFC 2136
  • http//www.ietf.org/html.charters/dnsind-charter.h

DNS Resource records
  • Every domain can have a set of resource records
    associated with it.
  • For single host, the most common resource record
    is its IP Address.
  • When a resolver gives a domain name to the DNS,
    it gets back the RRs associated with that name
  • TypeCNAME
  • name is alias name for some cannonical (the
    real) name
  • www.ibm.com is really
  • servereast.backup2.ibm.com
  • value is cannonical name
  • TypeA
  • name is hostname
  • value is IP address
  • TypeNS
  • name is domain (e.g. foo.com)
  • value is IP address of authoritative name server
    for this domain
  • TypeMX
  • value is name of mailserver associated with name

Resource Record
  • Domain name tells the domain to which this
    record applies.
  • Time_to_live field gives an indication of how
    stable the record is. Information that is highly
    stable is assigned large value such as 86400.
    Information that is highly volatile is assigned a
    smaller value as 60.
  • Class field is always IN for internet
    information. For non-internet information, other
    codes can be used.
  • Type field tells what kind of record this is.

Resource Records
  • The principal DNS resource records types.

Resource Records (2)
  • A portion of a possible DNS database for cs.vu.nl.

DNS protocol, messages
  • DNS protocol query and reply messages, both
    with same message format
  • msg header
  • identification 16 bit for query, reply to
    query uses same
  • flags
  • query or reply
  • recursion desired
  • recursion available
  • reply is authoritative

DNS protocol, messages
Name, type fields for a query
RRs in response to query
records for authoritative servers
additional helpful info that may be used
The World Wide Web
  • Architectural Overview
  • Static Web Documents
  • Dynamic Web Documents
  • HTTP The HyperText Transfer Protocol
  • Performance Ehnancements
  • The Wireless Web

Architectural Overview
  • (a) A Web page (b) The page reached by clicking
    on Department of Animal Psychology.

Architectural Overview (2)
  • The parts of the Web model.
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