Transcript Electronic Commerce

Electronic Commerce
Last Week
• The Internet - a network of thousands of
interconnected networks
– Interconnected Backbone supported by NSPs
– Access/Delivery sub-networks or ISPs
– Thousands of government/private/institutional network
• Internet Protocols
– Packet-switched network
– TCP/IP protocol
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Link layer
Network layer
Transport layer
Application layer
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Electronic Commerce
Last Week
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Routing of data packets and routing table
IP address and classes of IP addresses
Subnet addressing
Domain name (www.microsoft.com)
Domain name system (directory of domains names)
Uniform Resource Locator (http://microsoft.com/index.htm)
Other Internet protocols
– FTP, SMTP, POP, Telnet
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Electronic Commerce
This Week
• Internet utility programs
– Finger, Ping, Tracert
• Web Client-Server Architecture
– Two-tier and three-tier architecture
• Communication protocols in client-server architecture
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HTTP protocol
Common Gateway Interface (CGI)
Application Programming Interface (API)
Database Gateways (ODBC, IDC, ADO)
• Markup languages
– SGML, HTML, XML
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Internet Utility Programs
• TCP/IP supports a wide variety of utility programs
that permit more convenient and efficient use of the
Internet.
• Some popular utility programs are
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Finer
PING
Tracert
VisualRoute
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Internet Utility Programs
• Finger
– Finger is a utility program that runs on UNIX computers
– It allows a user to obtain limited information about other
network users from a remote computer
– One can use a Finger command to determine which users
are logged on to a particular network or gather some
information about a particular user in the network:
– userid of the user
– Time the user is logged in
– Name of the computer the user is logged in
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Internet Utility Programs
• PING
– PING (Packet InterNet Groper) tests connectivity between
two Internet hosts and determine if a host is active on the
network
– It works by sending a packet to the specified address and
waiting for a reply
– It is primarily used by network administrators to troubleshoot
Internet connection (whether a host is alive or not?)
– It provides performance data about the connection between
computers in the Internet, such as the number of hops it
takes to reach a data packet from a sender to the receiver
– Try ping www.microsoft.com or ping 148.129.129.31 from the
DOS prompt
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Internet Utility Programs
• Tracert/VisualRoute
– Tracert (TRACE RouTe) allows a user to trace the round trip
path between his/her computer and another computer on the
Internet.
– It calculates and displays the number of hops between two
computers and the time it takes to traverse the entire one
way path between them.
– The program works by sending a series of data packets to a
particular destination IP address on the Internet. Each
router on the path sends its IP address and the roundtrip
time it took to reach it
– A graphical traceroute program such as the VisualRoute
displays a graphical view of the route of the data packet
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Web Client-Server Architecture
• Introduction
• Every computer in the Internet runs a TCP/IP protocol. To an
end user, this lower level protocols is transparent
• A user interacts with the Internet through one of several
client/server applications
• An application running in one computer (client) requests a
service from another application running in another computer
(server)
• In this architecture, there are two major classes of software that
work together:
– Client software
– Server software
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Web Client-Server Architecture
• Client Software
– It usually resides on an end user’s computer and typically
requests services such as a Web page, database access, email, and ftp to the server.
– It does very little work.
• Server Software
– It usually resides on another computer that interprets
requests from the client, processes them, access services
from other computers if needed, and returns the result to the
client.
– It does most of the work
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Web Client-Server Architecture
• Web-Based Client-Server Application:
– The client is the Web browser (Internet Explorer, Netscape)
– The server is the Web server software (Internet Information
Server, Apache Server)
• Two types of Web-based client-server
applications architecture:
– Two-tier client-server architecture
– Three-tier client-server architecture
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Two-Tier Client-Server Architecture
• A two-tier architecture is one in which a client (tier1) and a
server (tier2) directs communications between them over the
Internet
• Steps of communication between a Web browser and Web
server:
– A user types a URL in the browser’s address line (and hits return)
or clicks a link on a Web page
– The browser then formats the request into a proper HTTP message
and passes it to the Internet
– A Web server always listens to a particular port (port 80) for any
incoming HTTP message
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Continued..
Two-Tier Client-Server Architecture
• Steps of communication (continued):
– When the server receives a request, it establishes a connection
with the client computer, locates the requested Web page and
formats it into an HTTP message
– It then sends it back to the browser, and the connection is broken.
– When the client receives the message, it recognizes that the page
is written in HTML code-something it can interpret, and displays the
formatted page
– If the page contains any graphics, another connection is made
between the client and the server
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Three-Tier Client-Server Architecture
• The first tier is the client, the second tier is the server, and the
third tier is typically a database or an application program
running in a different computer.
• From a software perspective, the three tires are: client
processes - tier1, Web services - tier2, and data services - tier 3
• From the hardware perspective, all three software could be in
three different computers, or in two computers, or in one
computer
• The database services, which comprise the third tier, are often
referred to as the backend machines/programs
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Three-Tier Client-Server Architecture
• When a client request a Web page from the server, the server
interprets it, and if it is found that the Web server needs to get
services from a database, it accesses the database, collects
necessary data, and returns the data formatted in HTML to the
client
• Electronic commerce sites often require a three-tier system with
its own hardware and software to keep track of customer
purchases/preferences; query inventory databases or updates
their catalog
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Communication Protocols in the
Client-Server Architecture
• HTTP protocol: Communication Between tier-1 and Tier-2:
– Whether it is a two-tier or a three-tier client-server architecture, a
common HTTP protocol is used to format a message sent between
a client in tier-1 and server in tier-2
• Communication protocols between tier-2 and tier-3:
– Several protocols are used to communicate between the Web
server and a database server.
– Protocols supported by Web servers are:
• Common Gateway Interface (CGI)
• Application Programming Interface (API)
• Open Database Connectivity (ODBC)
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Hypertext Transport Protocol (HTTP)
• HTTP is a lightweight, stateless protocol that browsers and
servers use to converse with each other.
• There are only seven commands in the protocol. Two of these
commands are: GET and POST. When a browser requests for a
page from the Web server, it uses the GET command.
• The HTTP is stateless because every request that a browser
makes opens a new connection that is immediately closed after
the document is returned. Thus the server cannot maintain state
information about successive requests in a straightforward
fashion.
• This statelessness represents a substantial problem for
electronic commerce applications, because an individual user is
likely to have a series of related interactions (browsing catalog,
select items, enter a payment information) within the application.
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Common Gateway Interface (CGI)
• CGI is a standard way of interfacing backend applications with
Web servers
• It is program written in a high-level language such as C/C++,
Visual Basic
• A CGI program is executed when requested by a browser
through an embedded call within a Web page
• Web pages that contain forms filed with text boxes, option
buttons, and list boxes supply information that CGI programs
can use to manipulate databases, store information, or retrieve
data
• CGI is known as a server-side solution, because all the
processing occurs in the Web server, not in the client computer
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Application Programming Interface (API)
• A CGI program is called every time there is request of a Web
page that contains a CGI program. This causes significant
processing burden in a high-traffic Web server
• Application Programming Interface or API is a set of protocols
that uses “multithreading,” that is, it only invokes a single
instance of the program to handle multiple user requests of the
dynamic Web pages
• API is more efficient than CGI, as CGI requires an individual
program to be brought to the Web server memory when
requested by multiple users
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Database Gateways
• A database gateway eliminates the need of creating customized
CGI program to access various databases produced by different
vendors
• Open database connectivity (ODBC) is a tool used by programs,
including a Web page, to communicate with a database
• Internet Database Connector (IDC) is a technology developed to
access and manipulate data from a database
• ActiveX Data Object (ADO) is another tool developed by
Microsoft that is also used to access and manipulate data from a
database.
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In-Class Work
• Create an order processing database in Microsoft Access where
a customer book order can be stored and the information can be
used by the inventory personnel to fulfill the order.
• The database should contain entities such as
– customer, book, order
• It should contain a order-entry form
• It should also contain a report on the books ordered by customer
and then by total amount
• Any other enhancement!
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