Bài giảng Web technologies and e-Services - Bài 1: Overview - Nguyễn Bình Minh
IT4409: Web Technologies and e-Services
Term 2020-2
Instructor: Dr. Thanh-Chung Dao
Slides by Dr. Binh Minh Nguyen
Department of Information Systems
School of Information and Communication Technology
Hanoi University of Science and Technology
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Reasonable Questions
• What is the World Wide Web?
• Is it the same thing as the Internet?
• Who invented it?
• How old is it?
• How does it work?
• What kinds of things can it do?
• What does it have to do with programming?
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Web ¹ Internet
• Internet : a physical network connecting millions of computers using the same protocols for
sharing/transmitting information (TCP/IP)
§ in reality, the Internet is a network of smaller networks
• World Wide Web: a collection of interlinked multimedia documents that are stored on the
Internet and accessed using a common protocol (HTTP)
Key distinction: Internet is hardware; Web is software along with data,
documents, and other media
Many other Internet-based applications exist
e.g., email, telnet, ftp, usenet, instant messenging services, file-sharing services, …
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(A Very Brief) History of the Internet
• the idea of a long-distance computer network traces back to early 60's
§ Joseph Licklider at M.I.T. (a “time-sharing network of computers”)
§ Paul Baran at Rand (tasked with designing a “survivable” communications
system that could maintain communication between end points even after
damage from a nuclear attack)
§ Donald Davies at National Physics Laboratory in U.K.
• in particular, the US Department of Defense was interested in the
development of distributed, decentralized networks
§ survivability (i.e., network still functions despite a local attack)
§ fault-tolerance (i.e., network still functions despite local failure)
contrast with phone system, electrical system which are highly
centralized services
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The Internet
• In 1969, Advanced Research Project Agency funded the ARPANET
§ connected computers at UC Los Angeles, UC Santa Barbara, Stanford Research
Institute, and University of Utah
§ allowed researchers to share data, communicate
56Kb/sec communication lines (vs. 110 b/sec over phone lines)
• Technical origin
§ One of earliest attempts to network heterogeneous, geographically dispersed
computers
§ Email first available on ARPANET in 1972 (and quickly very popular!)
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The Internet
• Open-access networks
§ Regional university networks (e.g., SURAnet)
§ CSNET for CS departments not on ARPANET
• NSFNET (1985-1995)
§ Primary purpose: connect supercomputer centers
§ Secondary purpose: provide backbone to connect regional networks
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The 6 supercomputer centers connected by the early NSFNET backbone
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Internet Growth
• throughout the 70's, the size of the ARPANET doubled every year
§ first ARPANET e-mail sent in 1971
§ decentralization mades adding new computers easy
§ TCP/IP developed in the mid 1970s for more efficient packet routing
§ migration of ARPANET to TCP/IP completed 1 January, 1983
§ ~1000 military & academic host computers connected by 1984
• in 80‘s, U.S. government took a larger role in Internet development
§ created NSFNET for academic research in 1986
§ ARPANET was retained for military & government computers
• by 90's, Internet connected virtually all colleges & universities
§ businesses and individuals also connecting as computing costs fell
§ ~1,000,000 computers by 1992
• in 1992, control of the Internet was transferred to a non-profit organizations
§ Internet Society:
Internet Engineering Task Force
Internet Architecture Board
Internet Assigned Number Authority
World-Wide-Web Consortium (W3C)
. . .
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Internet Growth (cont.)
Computers
on
Internet has exhibited exponential growth,
doubling in size every 1-2 years
(stats from Internet Software Consortium)
the Internet
Year
(at any one
time?)
2011
2006
2004
2002
2000
1998
1996
1994
1992
1990
1988
1986
1984
1982
~605,000,000
439,286,364
285,139,107
162,128,493
93,047,785
36,739,000
12,881,000
3,212,000
992,000
United Kingdom has 52.7 million users (approx.
83.6% of the population)
313,000
56,000
5,089
1,024
235
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Internet users in Vietnam
From dammio
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(A Very Brief) History of the Web
• the idea of hypertext (cross-linked and inter-linked documents) traces back to
Vannevar Bush in the 1940's
§ online hypertext systems began to be developed in 1960's
e.g., Ted Nelson and Andy van Dam's Hypertext Editing System (HES), Doug Englebert's
NLS (oN-Line System)
§ in 1987, Apple introduced HyperCard (a hypermedia system that predated the WWW)
• in 1989, Tim Berners-Lee at the European Particle Physics Laboratory (CERN)
designed a hypertext system for linking documents over the Internet
§ designed a (Non-WYSIWYG) language for specifying document content
• evolved into HyperText Markup Language (HTML)
§ designed a protocol for downloading documents and interpreting the content
• evolved into HyperText Transfer Protocol (HTTP)
§ implemented the first browser -- text-based, no embedded media
the Web was born!
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History of the Web (cont.)
• the Web was an obscure, European research tool until 1993
• in 1993, Marc Andreessen and Eric Bina (at the National Center for
Supercomputing Applications, a unit of the University of Illinois) developed
Mosaic, one of the early graphical Web browsers that popularized the WWW for
the general public (Erwise was the first one, ViolaWWW the second)
§ the intuitive, clickable interface helped make hypertext accessible to the masses
§ made the integration of multimedia (images, video, sound, …) much easier
§ Andreessen left NCSA to found Netscape in 1994
cheap/free browser further popularized the Web (75% market share in 1996)
• in 1995, Microsoft came out with Internet Explorer
• Opera web browser released in 1996
• Netscape bought by AOL in 1998 for US$4.2 billion in stock
• Firefox web browser, version 1.0, released in 2004
• Google Chrome released in 2008
• today, the Web is the most visible aspect of the Internet
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Popular websites in Vietnam
From dammio
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World Wide Web
• The Web is the collection of machines (Web servers) on the Internet that
provide information, particularly HTML documents, via HTTP.
• Machines that access information on the Web are known as Web clients.
A Web browser is software used by an end user to access the Web.
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Hypertext Transport Protocol (HTTP)
• HTTP is based on the request-response communication model:
§ Client sends a request
§ Server sends a response
• HTTP is a stateless protocol:
§ The protocol does not require the server to remember anything about the client
between requests.
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HTTP
• Normally implemented over a TCP connection (80 is standard
port number for HTTP)
• Typical browser-server interaction:
§ User enters Web address in browser
§ Browser uses DNS to locate IP address
§ Browser opens TCP connection to server
§ Browser sends HTTP request over connection
§ Server sends HTTP response to browser over connection
§ Browser displays body of response in the client area of the browser window
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HTTP Request
Structure of the request:
§ start line
§ header field(s)
§ blank line
§ optional body
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HTTP Request
Structure of the request:
§ start line
§ header field(s)
§ blank line
§ optional body
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HTTP Request
Start line
§ Example: GET / HTTP/1.1
Three space-separated parts:
§ HTTP request method
§ Request-URI (Uniform Resource Identifier)
§ HTTP version
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HTTP Request
Start line
§ Example: GET / HTTP/1.1
Three space-separated parts:
§ HTTP request method
§ Request-URI
§ HTTP version
We will cover 1.1, in which version part of start line must be exactly as shown
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HTTP Request
Start line
§ Example: GET / HTTP/1.1
Three space-separated parts:
§ HTTP request method
§ Request-URI
§ HTTP version
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HTTP Request
• Uniform Resource Identifier (URI)
§ Syntax: scheme : scheme-depend-part
Ex: in http://www.example.com/
the scheme is http
§ Request-URI is the portion of the requested URI that follows the host name (which is
supplied by the required Host header field)
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URI
• URI’s are of two types:
§ Uniform Resource Name (URN)
o Can be used to identify resources with unique names, such as books (which
have unique ISBN’s)
o Scheme is urn
§ Uniform Resource Locator (URL)
o Specifies location at which a resource can be found
o In addition to http, some other URL schemes are https, ftp, mailto,
and file
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HTTP Response
Structure of the response:
§ status line
§ header field(s)
§ blank line
§ optional body
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HTTP Response
Structure of the response:
§ status line
§ header field(s)
§ blank line
§ optional body
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HTTP Response
Status line
§ Example: HTTP/1.1 200 OK
Three space-separated parts:
§ HTTP version
§ status code
§ reason phrase (intended for human use)
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HTTP Response
Status code
§ Three-digit number
§ First digit is class of the status code:
1=Informational
2=Success
3=Redirection (alternate URL is supplied)
4=Client Error
5=Server Error
§ Other two digits provide additional information
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HTTP Response
Structure of the response:
§ status line
§ header field(s)
§ blank line
§ optional body
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HTTP Response
Common header fields:
§ Connection, Content-Type, Content-Length
§ Date: date and time at which response was generated (required)
§ Location: alternate URI if status is redirection
§ Last-Modified: date and time the requested resource was last
modified on the server
§ Expires: date and time after which the client’s copy of the resource
will be out-of-date
§ ETag: a unique identifier for this version of the requested resource
(changes if resource changes)
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HTTP Request/Response Examples
{
Trying 192.0.34.166...
(192.0.34.166).
Connect
Escape character is ’^]’.
GET / HTTP/1.1
Send
Request
{
HTTP/1.1 200 OK
Date: Thu, 09 Oct 2003
20:30:49 GMT
…
Receive
Response
{
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Web Browsers
First graphical browser running on general-purpose platforms:
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Web Browsers
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Web Browsers
Primary tasks:
§ Convert web addresses (URL’s) to HTTP requests
§ Communicate with web servers via HTTP
§ Render (appropriately display) documents returned by a server
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Static vs. Dynamic pages
• most Web pages are static
§ contents (text/links/images) are the same each time it is accessed
e.g., online documents, most homepages
HyperText Markup Language (HTML) is used to specify text/image format
• as the Web continues to move towards more and more online services and e-
commerce continues to grow, Web pages must also provide dynamic content
§ pages can be fluid, changeable (e.g., rotating banners)
§ must be able to react to the user's actions, request and process info, tailor services
e.g., amazon.com
• this course is about applying your programming skills to the development of
dynamic Web pages and applications
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Web server/client
Server
Client
1. HTTP request for image
2. HTTP response containing image
Web
Server
Browser
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Client Caching
Server
Client
1. HTTP request for image
2. HTTP response containing image
Web
Server
Browser
3. Store image
Cache
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Client Caching
Server
Client
Web
Server
Browser
I need that
image
again…
Cache
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Client Caching
Server
Client
This…
HTTP request for image
Web
Server
Browser
HTTP response containing image
I need that
image
again…
Cache
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Client Caching
Server
Client
Web
Server
Browser
I need that
image
again…
Get
image
… or this
Cache
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Client Caching
• Cache advantages
§ (Much) faster than HTTP request/response
§ Less network traffic
§ Less load on server
• Cache disadvantage
§ Cached copy of resource may be invalid (inconsistent with remote version)
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