Introduction to the Web

1
Introduction to the Web
2
Prerequisites

• Basic computer skills
• Experience using the World Wide Web
• Experience developing object-oriented software

3
Learning Objectives

• Overview of Web and Internet technologies
• Review of existing Web programming technologies

4
Agenda

• Internet Technologies
• Programming Languages and Paradigms
• Programming the Web

5
Internet Technologies The World Wide Web

• A way to access and share information
• Technical papers, marketing materials, recipes,
  ...
• A huge network of computers the Internet
• Graphical, not just textual
• Information is linked to other information
• Application development platform
• Shop from home
• Provide self-help applications for customers and
  partners

6
Internet TechnologiesWWW Architecture
PC/Mac/Unix Browser
Client
Request http//www.msn.com/default.asp
TCP/IP
Network
Response lthtmlgtlt/htmlgt
Web Server
Server
7
Internet TechnologiesWWW Architecture

• Client/Server, Request/Response architecture
• You request a Web page
• e.g. http//www.msn.com/default.asp
• HTTP request
• The Web server responds with data in the form of
  a Web page
• HTTP response
• Web page is expressed as HTML
• Pages are identified as a Uniform Resource
  Locator (URL)
• Protocol http
• Web server www.msn.com
• Web page default.asp
• Can also provide parameters ?nameLeon

8
Internet TechnologiesWeb Standards

• Internet Engineering Task Force (IETF)
• http//www.ietf.org/
• Founded 1986
• Request For Comments (RFC) at http//www.ietf.org/
  rfc.html
• World Wide Web Consortium (W3C)
• http//www.w3.org
• Founded 1994 by Tim Berners-Lee
• Publishes technical reports and recommendations

9
Internet TechnologiesWeb Design Principles

• Interoperability Web languages and protocols
  must be compatible with one another independent
  of hardware and software.
• Evolution The Web must be able to accommodate
  future technologies. Encourages simplicity,
  modularity and extensibility.
• Decentralization Facilitates scalability and
  robustness.

10
Internet TechnologiesHypertext Markup Language
(HTML)

• The markup language used to represent Web pages
  for viewing by people
• Designed to display data, not store/transfer data
• Rendered and viewed in a Web browser
• Can contain links to images, documents, and
  other pages
• Not extensible
• Derived from Standard Generalized Markup Language
  (SGML)
• HTML 3.2, 4.01, XHTML 1.0

11
Internet TechnologiesHTML Forms

• Enables you to create interactive user interface
  elements
• Buttons
• Text boxes
• Drop down lists
• Check boxes
• User fills out the form and submits it
• Form data is sent to the Web server via HTTP when
  the form is submitted

12
Internet TechnologiesHypertext Transport
Protocol (HTTP)

• The top-level protocol used to request and return
  data
• E.g. HTML pages, GIFs, JPEGs, Microsoft Word
  documents, Adobe PDF documents, etc.
• Request/Response protocol
• Methods GET, POST, HEAD,
• HTTP 1.0 simple
• HTTP 1.1 more complex

13
Internet TechnologiesHTTP Request
Method
File
HTTP version
Headers

• GET /default.asp HTTP/1.0
• Accept image/gif, image/x-bitmap, image/jpeg,
  /
• Accept-Language en
• User-Agent Mozilla/1.22 (compatible MSIE 2.0
  Windows 95)
• Connection Keep-Alive
• If-Modified-Since Sunday, 17-Apr-96 043258 GMT

Blank line
Data none for GET
14
Internet TechnologiesHTTP Response
HTTP version
Status code
Reason phrase
Headers
HTTP/1.0 200 OK Date Sun, 21 Apr 1996 022042
GMT Server Microsoft-Internet-Information-Server/
5.0 Connection keep-alive Content-Type
text/html Last-Modified Thu, 18 Apr 1996
173905 GMT Content-Length 2543 ltHTMLgt Some
data... blah, blah, blah lt/HTMLgt
Data
15
Internet TechnologiesHTTP Server Status Codes
Code Description
200 OK
201 Created
301 Moved Permanently
302 Moved Temporarily
400 Bad Request not understood
401 Unauthorized
403 Forbidden not authorized
404 Not Found
500 Internal Server Error
16
Internet TechnologiesHTTP

• HTTP is a stateless protocol
• Each HTTP request is independent of previous and
  subsequent requests
• HTTP 1.1 introduced keep-alive for efficiency
• Statelessness has a big impact on how scalable
  applications are designed

17
Internet TechnologiesCookies

• A mechanism to store a small amount of
  information (up to 4KB) on the client
• A cookie is associated with a specific web site
• Cookie is sent in HTTP header
• Cookie is sent with each HTTP request
• Can last for only one session (until browser is
  closed) or can persist across sessions
• Can expire some time in the future

18
Internet TechnologiesHTTPS

• A secure version of HTTP
• Allows client and server to exchange data with
  confidence that the data was neither modified nor
  intercepted
• Uses Secure Sockets Layer (SSL)/Transport Layer
  Security (TLS)

19
Internet TechnologiesURIs, URLs and URNs

• Uniform Resource Identifier (URI URL or URN)
• Generic term for all textual names/addresses
• Uniform Resource Locator (URL)
• The set of URI schemes that have explicit
  instructions on how to access the resource over
  the Internet, e.g. http, ftp, gopher
• Uniform Resource Name (URN)
• 1) A URI that has an institutional commitment to
  availability, etc.
• 2) A particular scheme intended to identify
  resources
• e.g. urnschemashttpmailsubject

20
Internet TechnologiesMultipurpose Internet Mail
Extensions (MIME)

• Defines types of data/documents
• text/plain
• text/html
• image/gif
• image/jpeg
• audio/x-pn-realaudio
• audio/x-ms-wma
• video/x-ms-asf
• application/octet-stream

21
Internet TechnologiesMIME

• Specifies character sets, e.g. ASCII
• Supports multi-part messages
• Originally designed for email, but also used in
  other places, such as HTTP

22
Internet TechnologiesBrowsers

• Client-side application
• Requests HTML from Web server and renders it
• Popular browsers
• Netscape
• Internet Explorer
• Opera
• others
• Also known as a User Agent

23
Internet TechnologiesClients Servers

• Client and Server computers both have
• CPU
• Memory
• I/O
• Disks
• Network
• Bus
• Multi-tasking operating system
• Applications

24
Internet TechnologiesClients Servers

• Clients
• Generally supports a single user
• Optimized for responsiveness to user
• User interface, graphics
• Servers
• Supports multiple users
• Optimized for throughput
• More CPUs (SMP), memory, disks (SANs), I/O
• Provide services (e.g. Web, file, print,
  database, e-mail, fax, transaction, telnet,
  directory)

25
Internet TechnologiesProxy Servers Firewalls

• Proxy Server
• A server that sits between a client (running a
  browser) and the Internet
• Improves performance by caching commonly used Web
  pages
• Can filter requests to prevent users from
  accessing certain Web sites
• Firewall
• A server that sits between a network and the
  Internet to prevent unauthorized access to the
  network from the Internet

26
Internet TechnologiesNetworks

• Network an interconnected collection of
  independent computers
• Why have networks?
• Resource sharing
• Reliability
• Cost savings
• Communication
• Web technologies add
• New business models e-commerce, advertising
• Entertainment
• Applications without a client-side install

27
Internet TechnologiesNetworks

• Network scope
• internet a collection of connected networks
• Internet a specific world-wide network based on
  TCP/IP, used to connect companies, universities,
  governments, organizations and individuals.
  Originated as ARPANET, funded by the US DoD.
• intranet a network based on Internet
  technologies that is internal to a company or
  organization
• extranet a network based on Internet
  technologies that connects one company or
  organization to another

28
Internet TechnologiesNetworks

• Network technology is largely determined by
  scale
• Local Area Network (LAN) Span up to a few
  kilometers. Bus vs. ring topologies
• Wide Area Networks (WAN) Can span a country or
  continent. WANs use routers as intermediate
  nodes to connect transmission lines

29
Internet TechnologiesNetworks

• Network technology
• Broadcasting
• Packets of data are sent from one machine and
  received by all computers on the network
• Multicast packets are received by a subset of
  the machines on a network
• Point-to-point
• Packets have to be routed from one machine to
  another there many be many paths
• In general, geographically localized networks use
  broadcasting, while disperse networks use
  point-to-point

30
Internet TechnologiesNetworks
OSI Model Layers
TCP/IP Protocol Architecture Layers
TCP/IP Protocol Suite
Application Layer
Presentation Layer
Application Layer
Telnet
FTP
SMTP
DNS
RIP
SNMP
HTTP
Session Layer
Host-to-Host Transport Layer
TCP
UDP
Transport Layer
Network Layer
Internet Layer
IP
ICMP
IGMP
ARP
Data Link Layer
Network Interface Layer
Token Ring
Ethernet
ATM
Frame Relay
Physical Layer
31
Internet TechnologiesNetwork Protocol Stack
HTTP
HTTP
TCP
TCP
IP
IP
Ethernet
Ethernet
32
Internet TechnologiesNetworks - Internet Layer

• Internet Protocol (IP)
• Responsible for getting packets from source to
  destination across multiple hops
• Not reliable
• IP address 32 bit value usually written in
  dotted decimal notation as four 8-bit numbers (0
  to 255) e.g. 130.50.12.4

33
Internet TechnologiesNetworks - Transport Layer

• Provides efficient, reliable and cost-effective
  service
• Uses the Sockets programming model
• Ports identify application
• Well-known ports identify standard services
  (e.g. HTTP uses port 80, SMTP uses port 25)
• Transmission Control Protocol (TCP)
• Provides reliable, connection-oriented byte
  stream
• UDP
• Connectionless, unreliable

34
Internet TechnologiesNetworks - Application Layer

• Telnet Remote sessions
• File Transfer Protocol (FTP)
• Network News Transfer Protocol (NNTP)
• Simple Network Management Protocol (SNMP)
• Simple Mail Transfer Protocol (SMTP)
• Post Office Protocol (POP3)
• Interactive Mail Access Protocol (IMAP)

35
Internet TechnologiesNetworks - Domain Name
System (DNS)

• Provides user-friendly domain names, e.g.
  www.msn.com
• Hierarchical name space with limited root
  names
• DNS servers map domain names to IP addresses

• .com
• .net
• .gov
• .edu

• .org
• .mil
• .in

36
Internet TechnologiesExtensible Markup Language
(XML)

• Represents hierarchical data
• A meta-language a language for defining other
  languages
• Extensible
• Useful for data exchange and transformation
• Simplified version of SGML

37
Agenda

• Internet Technologies
• Programming Languages and Paradigms
• Programming the Web
• .NET Overview

38
Programming Languages

• Machine code
• Assembly language
• High-level languages
• Fortran, LISP, Cobol
• C, Pascal, Basic, Smalltalk
• C, Eiffel
• Java, C
• Scripting languages
• Shell scripts, Perl, TCL, Python, JavaScript,
  VBScript

39
Programming Paradigms

• Unstructured programming
• Structured programming
• Object-oriented programming
• Component-based programming
• Event-based programming

40
Programming ParadigmsUnstructured Programming

• See Go To Statement Considered Harmful at
  http//www.acm.org/classics/oct95/

41
Programming ParadigmsStructured Programming

• Sequence
• Conditional
• if then else
• switch
• Looping
• for i from 1 to n
• do while
• do until
• Functions
• Exceptions

42
Programming ParadigmsObject-Oriented Programming

• Objects have data and behavior
• Data members, fields, variables, slots,
  properties
• Behavior methods, functions, procedures
• Using objects is easy
• First instantiate the type of object desired
• Then call its methods and get/set its properties
• Designing new types of objects can be hard
• Design goals often conflict simplicity,
  functionality, reuse, performance

43
Programming ParadigmsObject-Oriented Programming

• Key object-oriented concepts
• Identity
• Encapsulation
• Data behavior
• Information hiding (abstraction)
• Classes vs. instances
• Polymorphism
• Interfaces
• Delegation, aggregation
• Inheritance
• Patterns

44
Programming ParadigmsComponent-Based Programming

• Components
• Independent modules of reuse and deployment
• Coarser-grained than objects (objects are
  language-level constructs)
• Includes multiple classes
• Often language-independent
• In the general case, the component writer and the
  component user dont know each other, dont work
  for the same company, and dont use the same
  language

45
Programming ParadigmsComponent-Based Programming

• Component Object Model (COM)
• Initial Microsoft standard for components
• Specifies a protocol for instantiating and using
  components in-process, across processes or
  across machine boundaries
• Basis for ActiveX, OLE, and many other
  technologies
• Can be created in Visual Basic, C, .NET,
• Java Beans
• Java standard for components
• Not language-independent

46
Programming ParadigmsEvent-Based Programming

• When something of interest occurs, an event is
  raised and application-specific code is executed
• Events provide a way for you to hook in your own
  code into the operation of another system
• Event callback
• User interfaces are all about events
• onClick, onMouseOver, onMouseMove
• Events can also be based upon time or
  interactions with the network, operating system,
  other applications, etc.

47
Agenda

• Internet Technologies
• Programming Languages and Paradigms
• Programming the Web
• .NET Overview

48
Programming the WebClient-Side Code

• What is client-side code?
• Software that is downloaded from Web server to
  browser and then executes on the client
• Why client-side code?
• Better scalability less work done on server
• Better performance/user experience
• Create UI constructs not inherent in HTML
• Drop-down and pull-out menus
• Tabbed dialogs
• Cool effects, e.g. animation
• Data validation

49
Programming the WebClient-Side Technologies

• DHTML/JavaScript
• COM
• ActiveX controls
• COM components
• Remote Data Services (RDS)
• Java
• Plug-ins
• Helpers
• Remote Scripting

50
Programming the WebDynamic HTML (DHTML)

• Script that is embedded within an HTML page
• Usually written in JavaScript (ECMAScript,
  JScript) for portability
• Internet Explorer also supports VBScript and
  other scripting languages
• Each HTML element becomes an object that has
  associated events (e.g. onClick)
• Script provides code to respond to browser events

51
Programming the WebDHTML

• The DHTML Document Object Model (DOM)

window
history
document
location
screen
navigator
frames
event
all
location
children
selection
forms
body
links
text
button
radio
textarea
select
password
checkbox
submit
option
file
reset
52
Programming the WebServer-Side Code

• What is server-side code?
• Software that runs on the server, not the client
• Receives input from
• URL parameters
• HTML form data
• Cookies
• HTTP headers
• Can access server-side databases, e-mail servers,
  files, mainframes, etc.
• Dynamically builds a custom HTML response for a
  client

53
Programming the WebServer-Side Code

• Why server-side code?
• Accessibility
• You can reach the Internet from any browser, any
  device, any time, anywhere
• Manageability
• Does not require distribution of application code
• Easy to change code
• Security
• Source code is not exposed
• Once user is authenticated, can only allow
  certain actions
• Scalability
• Web-based 3-tier architecture can scale out

54
Programming the WebServer-Side Technologies

• Common Gateway Interface (CGI)
• Internet Server API (ISAPI)
• Netscape Server API (NSAPI)
• Active Server Pages (ASP)
• Java Server Pages (JSP)
• Personal Home Page (PHP)
• Cold Fusion (CFM)
• ASP.NET

55
Programming the Web Active Server Pages (ASP)

• Technology to easily create server-side
  applications
• ASP pages are written in a scripting language,
  usually VBScript or JScript
• An ASP page contains a sequence of static HTML
  interspersed with server-side code
• ASP script commonly accesses and updates data in
  a database

56
Programming the WebASP
ASP page (static HTML, server-side logic)
57
Architectures

• N Tier
• Application Servers
• Middleware
• Intranets

58
What to Know About Architectures

• Evolution of Architectures
• Evolution of COM
• Definitions
• ASP
• Middleware
• Database transparency
• ADO

59
Client/Server

• Client/Server evolves along the line of PC
  computing and Microsoft
• PC moved from complement to substitute for Host
  systems
• 80s PCs were personal
• 90s PCs were departmental
• 00s PCs are enterprise wide platforms

60
Key Problems of Client/Server

• Scalability
• Manageability
• Complexity
• Ease of Use
• Application Development

61
Network Architectures

• Host-based networks the host computer performs
  virtually all of the work
• Client-based networks the client computer
  performs virtually all of the work
• Client-server networks the work is shared
  between the hosts and clients

62
Functions

• The work done by any application program can be
  divided into four general functions
• data storage
• data access logic
• application logic
• presentation logic

63
Host-Based Architectures
64
Host-Based Architectures

• Scalability
• Pros provide large scale access
• Cons expensive, lumpy, slow
• Centralized Management
• Complexity
• Poor user interface
• Application backlog low level tools,
  specialized knowledge

65
Client-Based Architectures

• Evolution of standalone PC to fill gaps in
  departmental computing needs

66
Client-Based Architectures

• Server acts as a remote disk drive.
• Client does all the processing.
• Searches slow down the network, each query has
  the server pass the entire database over the
  network.

67
Client-Based Architectures

• Scalability
• Pros cheap easy to add a station up to limits
• Cons severely limited by bandwidth/architecture
  
• Cons changes to application must be made on
  server and all clients
• Decentralized Management
• Complexity
• Graphical user interface
• Off the shelf applications high level tools
• Custom apps difficult to develop

68
Two Tier Client-Server

• Moves data access logic to server - decreases
  congestion
• Ease application development object oriented
  programming

69
Two Tier Client/Server

• Improved Scalability less data traffic
• An SQL request is generated in the client and
  transmitted to the server. The DBMS searches
  locally and returns only matching records greatly
  reducing data traffic.

70
COM - Component Object Model

• Rapid development lower costs by using ready
  made building blocks
• Components called like subroutines
• Two tier system - components downloaded to the
  client to execute, uses lots of bandwidth bogs
  down WANs and enterprise networks

71
Three Tier Client/Server

• Application server stores executes components
  for clients
• Easier management - centralizing application
  logic
• Reduces network traffic
• Optimizes network processing - Lower load on
  client. Can use thin clients, NCs, older PCs,

72
Three Tier Object Models

• CORBA Common Object Request Broker Architecture
• DCOM (MS) Distributed Component Object Model
• Allows components to be executed remotely with
  results sent back to client

73
Three Tier Client/Server

• API Application Programming Interface and three
  tier architecture brings the power of layering
  logic
• layering logic - change a layer without changing
  the others
• Application logic - (ex. Tax software)

74
Web Mail as 3 Tier System
75
Systems Management Performance Web Sites MS
Windows DNA

• Front End stateless load balancing, cloned
  systems
• Back End stateful, partitioning

76
N-Tier Architecture
77
What is a Web Application?
HTTP Clients
Services
IIS
Active Server Pages
Transaction server
Script Logic
Message Queuing
COM
Commerce
Databases and Directories
78
Architecture Tiers Business Logic

• COM - Component Object Model
• Service accessibility
• Visual Basic, C, Java, Cobol, Pascal
• Used from Active Server Pages
• COM components provide
• Encapsulation of internal details
• Modularity for code reuse
• Intellectual Property Security

79
N Tier Intranet - Scalability
80
N Tier Architecture
SQL Server
Internet InformationServer \ LDAP Server
MTS
Directory
HTTP
WebBrowser
Components
DCOM
MicrosoftExchange
LDAP
Others
MSMQ
Presentation
Business logic
Data services
81
Architecture Of A Commerce Site
Commerce Server Supplied Components
HTML
.ASP
Data
IIS
ltbrgt Tha ltAgt Cop
. lt/ Server .
SQL, Oracle, (ODBC compliant)
Commerce Server Components
82
Commerce Accessing The Data

• Data is accessed using ADO and any ODBC compliant
  database can be easily used

83
Middleware

• Conversion layer, sits between client and
  database
• Database transparency - middleware translates DB
  using OLE DB (API)
• Data access logic (ADO, OLE DB)
• application written independent of source of
  database
• integrate data from incompatible sources
• Allows multi-vendor solutions

84
Benefits of Client-Server Architectures

• Scalability
• Manageable
• Cost Effective - PC hardware is more than 1000
  times cheaper than mainframe hardware for the
  same computing power.
• Complexity easy on user, tough on IT

85
Intranets

• In-house web site not accessible by public
• Gives benefits of three tier model
• Low bandwidth requirements
• Thin client
• Lower management cost /deployment cost
• Scalability
• Reduces complexity - cross platform
  interoperability, standard interface
• Emerging tools and standards HTML not suited to
  applications, DHTML, XML, Biztalk

86
Elements of the Intranet

• Client - Browser
• navigation, interpretation of HTML from server,
  light processing
• dynamic HTML - does processing on client Web
  pages function more like regular software, better
  control of interface
• Server -
• serves up HTML to client via HTTP, lower
  bandwidth needed between server and client
• Active Server Pages (.asp), script language
  embedded in HTML pages that generates HTML output
  from remote procedure call on server