Introduction to Web Technology

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5 Νοε 2013 (πριν από 3 χρόνια και 1 μήνα)

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IntroductiontoWebTechnology
DianaInkpen
UniversityofOttawa
SchoolofInformationTechnologyandEngineering
1
Contentofthecourse

TheInternetandtheWWW.

InternetConnectivity.

BasicInternetServices.

NavigatingtheWWW.

BuildingWebpages(HTML).

Searchengines.InformationRetrieval.

Business,Issues,andControversies.
2
WhatistheInternet?
3
WhatistheInternet?

TheInternetisaglobal
networkofnetworks
thatenables
computersofallkindstodirectlyandtransparently
communicateandshareservicesthroughouttheworld.
4
TheInternetandtheWWW

EvolutionoftheInternet.

FeaturesoftheInternet.

FeaturesoftheWWW.

Webservers.

Webclients.

SearchEngines
5
WhatyearwastheInternetborn?
6
TheevolutionoftheInternet

In1969theprecursorofInternetisborn:ARPAnet.

ARPA=AdvancedResearchProjectsAgencysponsored
bytheAmericanDepartmentofDefense(DOD).

Designedtoconnectmilitaryresearchcenters.
Distributed
computersystemabletosurviveanuclear
attack.

Fournodes:atUCLA(LosAngeles),StanfordResearch
Institute,UCSB(SantaBarbara),andUniversityofUtah.

Therewereinfacttwonetworks:MILnetandARPAnet.
7
TheevolutionoftheInternet
(2)

Problem:ARPAnetcouldconnectonlynetworksofthe
sametype.

In1970,ARPAstartsdevelopingtheTransmissionControl
Protocol/InternetProtocol(TCP/IP),atechnologyfor
connectingnetworksofdifferenttypes
(producedby
differentcompanies).

Othernetworksappear,suchasCSNETandBITNET.
8
TheevolutionoftheInternet
(3)

Theconceptof
internetworking
wasdeveloped.A
networkconnectsthrougha
gateway
thatfacilitates
communicationwithnetworksofdifferenttypes.

Thename
Internet
startstobeused.

In1980NSFnetiscreatedbyNationalScienceFoundation
toconnectsupercomputercentersforacademicresearch.
By1990,NSFnetreplacesARPAnet,whichceasesto
exists.
9
HowbigistheInternet?
Year
Computers
Newsgroups
WWWsites
1969
4
1977
100
1986
5,000
200
1990
300,000
1,000
1993
2mil
6,000
600
1994
3mil
10,000
10,000
1997
19mil
70,000
1mil
2002
350mil
100,000
1billion
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FeaturesoftheInternet

TheInternet=anetworkofnetworks.

Peoplearoundtheworldshareideas,information,
comments,andstories.
Popularservices:

Email(electronicmail)isthemostpopularservice.You
cansendandreceivemail(electronictext),fasterand
cheaperthansurfacemail.Exampleemailaddresses:
username@computer-addressdiana@site.uottawa.ca

Webbrowsingtofindinformation.Example:www.cnn.com
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FeaturesoftheInternet
(2)

Mailinglists:youcansubscribetolistsonvarious
subjectstoreceiveemails,youcanpost(send)messages,
youcanunsubscribe.Somelistsaremoderated.

Newsgroupsarecollectionsofmessagesonvarious
subjects.Examplecomp.internet

FTP(FileTransferProtocol).Youcancopyfilesfrom
onecomputertoanotherovertheInternet.
12
FeaturesoftheInternet
(3)

Telnetorremotelogin.Permitsyourcomputertolog
ontoanothercomputeranduseitasifyouwerethere.
Youneedtoprovidesyourusernameandpassword,for
securityreasons.

Chatrooms.Youcanexchangemessageswithother
people,anonymously(usinganickname).

Internetservicesforcompanies:e-commerce,etc.
13
HowdoesdatatravelonInternet?

Dataisdividedinto
packets
,thataretransmittedoverthe
Internet,andre-assembledatdestination.Nodedicated
connectionisneeded(Packetswitching).

Routing
=thepacketscanfollowdifferentroutesonthe
Internet.Theroutersreadtheaddressesanddirectthe
packets(usingtheirroutingtables).
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Internetrouting
Computer
Computer
Router
Computer
Computer
Router
Router
Computer
Router
Computer
Router
Computer
Computer
(host)
(host)
(host)
(host)
(host)
(host)
(host)
(host)
15
TCP/IPfamilyofprotocols

A
protocol
=setofrulesthatallowdifferentcomputersor
devicestocommunicatewitheachother.Implementedin
software.

IP(InternetProtocol)movespacketsbetweennodes.

IPforwardseachpacketbasedonadestinationaddress
(theIPnumber).

TCP(TransmissionControlProtocol)isresponsiblefor
verifyingthecorrectdeliveryofdatafromclienttoserver.

TCPaddssupporttodetecterrorsorlostdataandto
triggerretransmissionifneeded.
16
Internetaddresses

TheInternetauthoritiesassignrangesof
IPaddresses
to
differentorganizations.Theorganizationsassigngroups
oftheirnumberstodepartments.

IPaddress=fournumbers:
n.n.n.n
,where0

n

255.
Example:130.63.236.137

Domainnames
wereinventedinordertoavoidtheneed
tomemorizenumbers.
Example:ugate.site.uottawa.ca
17
Internetaddresses
(2)

DomainNameServers
(DNS)translatedomainnames
intoIPaddresses.

Hierarchicalstructure,readfromrighttoleft.

Top-leveldomains:

.com.org.net.edu.int.mil.gov

countrycodes:.ca.de.fr

Example:ugate.site.uottawa.ca
Example:www.microsoft.com
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Internetaddresses
(3)

WhoassignsIPnumbers?
InternetAssignedNumbersAuthority(IANA).

Whoassignsdomainnames?

Toplevel:TheInternetCorporationforAssigned
NamesandNumbers(ICANN).

Secondlevel:NetworkSolutionsInc.,andother
registrarsaccreditedbyICANN.
Seehttp://www.internic.org/foralist.
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FeaturesofWWW

WorldWideWeb(WWW,theWeb)=alinkedcollection
ofdocumentsresidingoncomputersconnectedtothe
Internet,namedWebservers.

Hypertext
=atextdocumentthatinclude
links
toother
documents.

Hypermedia
=alsoincludesimages,video,andsound.

WWWhypertextsystembeganatCERN(European
CentreforNuclearResearch)inGeneva,underTim
Berners-Lee,in1989.
20
FeaturesofWWW
(2)

Problem:ifthedocumentshavevariousformats,they
cannotbeviewedbyeveryone.

Textdocuments(ASCII)canbeviewedbyeveryone,but
theycannotencodelinks,format,andmultimedia.

ThedocumentsontheWeb(webpages)aretextfilesthat
containformatinformationcodedin
HyperTextMarkup
Language(HTML)
.
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Webpages(HTMLdocuments)

Textappearance:bold,italic,fontsize.

Linkstootherpages(hyperlinks).

Images,sound,videocanbeembedded.

Fill-informsallowinteractionwiththeuser.

Interfacestodatabases.DynamicHTMLpages.

Webpagescancontainexecutables,suchasJavaapplets.

Webprogramminglanguages:Java,Javascript,Perl.
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ExampleofHTMLpage

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




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Webservers

ThewebpagesareonWebservers.

WebserversrunsoftwarethatimplementsHTTP:httpd,
Apache.

OfferaccesstoacollectionofWebpages(aWWWsite).

URL=UniformResourceLocator.Uniquelyidentifya
webpage:http://server-name/directory/filename

Example:http://www.site.uottawa.ca/index.htm
Example:http://www.site.uottawa.ca/
24
Webclients

Browsers:Mosaic,NetscapeNavigator,InternetExplorer.

HTMLpagesaretextfilesthatcontaininformationabout
theirformat.

TheWebbrowserusesthisinformationtorecreatethe
pageonyourcomputer.
25
HyperTextTransferProtocol
HTTPactsasaninterfacebetweenaWebclientsoftware(i.e.
abrowsersuchasNetscapeNavigatororInternetExplorer)
andaWebserversoftware.A
server
canservemany
clients
.

Client’sHTTPrequestsconnectiontotheserver.

Server’sHTTPsendsbackserverstatus.

Client’sHTTPrequestsdocument.

Server’sHTTPsendsdocument(ifavailable).

Connectionisbrokenafterdocumentisdownloadedon
yourcomputer.Itisnotmaintainedwhileyouviewit.
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Searchengines

FindandretrieveinformationontheWWW.

Documentindexing=eachdocumentontheWebis
representedintheindexbyitsURLandsome
keywords
.

AsearchenginerunsonaWebserver.Youaccessit
throughanHTMLinterface.Youprovideyourqueryin
thefill-inform.ThesearchenginewillgiveyouURLsof
pagesthatmatchyourquery.

Searchengines:Google,AltaVista,Yahoo,etc.

Meta-searchengines:Metacrawler,etc.
27
HowbigistheWeb?

Googleannounced(December2001)thattheitstotal
collectionofindexeddocumenthavepassed3billions.
Thisfigureisbrokendowninto:

2billionswebpages(HTMLdocuments,butalsoother
filessuchasAdobeAcrobatorMSWordfiles).

330millionsimages.

700millionsnewsgroupmessages.
28
Summary
Youlearned:

WhatistheInternet?

WhatistheWWW?

DatatransferontheInternet.

Hypertext,HTMLpages.

WebserversandWebclients.

Searchengines.
29
References
http://www.isoc.org/internet/
http://www.internet-guide.co.uk/
http://library.albany.edu/internet/
http://www.northernwebs.com/bc/
Books:
IntroductiontotheInternet,byScottD.James,2001
Hownetworkswork,byFrankDerflerandLesFreed,2000
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