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 Link layer Network layer Transport layer Application layer Electronic Commerce

Electronic Commerce Last Week 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 Electronic Commerce

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 HTTP protocol Common Gateway Interface (CGI) Application Programming Interface (API) Database Gateways (ODBC, IDC, ADO) Markup languages SGML, HTML, XML Electronic Commerce

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 Finer PING Tracert VisualRoute Electronic Commerce

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 Electronic Commerce

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 Electronic Commerce

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 Electronic Commerce

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 Electronic Commerce

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, e-mail, 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 Electronic Commerce

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 Electronic Commerce

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 Continued.. Electronic Commerce

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 Electronic Commerce

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 Electronic Commerce

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 Electronic Commerce

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) Electronic Commerce

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. Electronic Commerce

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 Electronic Commerce

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 Electronic Commerce

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. Electronic Commerce

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! Electronic Commerce