WHAT ARE INTERNET AND WEB TECHNOLOGIES?
Traditional networks are designed to share resources, like data (files) and printers these shared resources are called network services.
Today with the Internet, network services have become more distributed or decentralized, companies and individuals can share resources (mainly information) on a global scale. This global resource sharing is managed by internetworking servers.
1.0 Server implementations:
There are 2 main server operating system software Windows and UNIX. Linux is more like UNIX.
UNIX servers use special programs called daemons, the internet daemon is called inetd, this is used to start other Internet servers. The inetd has a super user access privilege which gives it permission to bind ports to any process it starts.
It is called a daemon because it waits and listens in the background until summoned by another process.
The inetd service runs when the UNIX or Linux system starts up, when the inetd daemon receives a request it launches other services to support the request.
Windows uses services to run internetworking servers. Services are similar to daemons as they wait in the background to be activated. Windows services must be set up by the user with administrator access privileges, which gives the service permission to bind to well known port numbers.
1.1Internetworking servers
1.1.1Web servers\HTTP servers
These send documents for viewing in web browsers. The web browser is a client application that requests documents from the web server, based on the URL that the user enters. The documents that the server sends may be from a disk archive or may be created dynamically when the client requests them.
HTTP servers work closely with the computer’s operating system because a web server is a high performance file sharing system. The performance of an HTTP server therefore depends on how well it works with a particular network operating system.
Access control
An important part of setting up and managing a web server is access control , most websites offer access to the general public; users do not need special permission to access such server resources, this type of access is called anonymous access. Some sites want to restrict access to particular resources, in this case an access control list defines the permissions for a resource by specifying which users and groups have access.
For example the website may offer certain documents only to registered or paying users.
Restricting access to server resources is based on a database of permitted users who must supply a password to access particular server information.
One of the biggest drawbacks of HTTP is that this protocol is stateless implying that: There is no track of the last known or current status of an application or process. As a result the Internet is stateless and each request for a new Web page is processed without any knowledge of previous pages requested.
Because maintaining state is extremely useful, programmers have developed a number of techniques to add state to the World Wide Web. These include server side scripting and client side scripting
1.1.2 Mail Servers
There are two ways to store and access internet email messages. That is:
1: IMAP/SMTP
2: POP3/SMTP
Let’s explain these with a scenario; if you successfully send an email message, the message would be stored in the appropriate server until the recipient downloads it from the server. The POP3 server responds to a request, asks for a password, then transmits the messages to the client.
SMTP stands for simple Mail Transfer Protocol, this protocol a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.
IMAP (Internet Message Access Protocol) and POP (Post Office Protocol) are both protocols for downloading emails from the mail server.
POP3
IMAP
Emails needs to be downloaded into desktop PC before being displayed, you may have the following problems for POP3 access:
You need to download all email again when using another desktop PC to check your email.
May get confused if you need to check email both in the office and at home.
The downloaded email may be deleted from the server depending on the setting of your email client.
Email is kept on server only downloaded when it is opened for display/view, it would gain the following benefits for IMAP access:
No need to download all email when using other desktop PC to check your email.
Easier to identify the unread email.
Outgoing email is stored only locally on the desktop PC.
Outgoing email can be filtered to a mailbox on server for accessibility from other machine.
Messages may be reloaded onto desktop PC several times due to the corruption of system files.
The occurrence of reloading messages from the server to PC is much less when compared to POP3.
Sometimes we attach files to an email these files are supposed to be opened and interpreted by the recipient browser, the attachments are labeled with its MIME type by the sender client application, and the recipient uses the MIME to display the information.
MIME is short for Multipurpose Internet Mail Extensions, a specification for formatting non-ASCII messages so that they can be sent over the Internet. Many e-mail clients nowsupport MIME, which enables them to send and receive graphics, audio, and video files via the Internet mail system. In addition, MIME supports messages in character sets other than ASCII.
In addition to e-mail applications, Web browsers also support various MIME types. This enables the browser to display or output files that are not in HTML format.
1.1.3Streaming Media Servers
Streaming media is designed to emulate traditional broadcast media e.g. radio and television but can provide on demand access to audiences of any size. Streaming media servers use UDP to achieve the effect of a real time broadcast. UDP (User Datagram Protocol) is a connectionless protocol that, like TCP, runs on top of IP networks. Unlike TCP/IP, UDP/IP provides very few error recovery services, offering instead a direct way to send and receive data grams over an IP network. It's used primarily for broadcasting messages over a network.
Unlike other content servers, the client does not receive the entire media file to present the data to the user; instead the client usually discards the streaming media data as it is being presented to the user.
Streaming technologies are becoming increasingly important with the growth of the Internet because most users do not have fast enough access to download large multimedia files quickly. With streaming, the client browser or plug-in can start displaying the data before the entire file has been transmitted.
For streaming to work, the client side receiving the data must be able to collect the data and send it as a steady stream to the application that is processing the data and converting it to sound or pictures. This means that if the streaming client receives the data more quickly than required, it needs to save the excess data in a buffer. If the data doesn't come quickly enough, however, the presentation of the data will not be smooth.
There are a number of competing streaming technologies emerging. For audio data on the Internet, the de facto standard is Progressive Network's RealAudio
Streaming media servers are well suited for intranet. Businesses and other organizations can use streaming media and corporate networks to distribute audio and video material, including employee meetings, training films and marketing material.
1.1.4 FTP Servers
Short for File Transfer Protocol, the protocol for exchanging files over the Internet. FTP works in the same way as HTTP for transferring Web pages from a server to a user's browser and SMTP for transferring electronic mail across the Internet in that, like these technologies, FTP uses the Internet's TCP/IP protocols to enable data transfer.
FTP is most commonly used to download a file from a server using the Internet or to upload a file to a server (e.g., uploading a Web page file to a server
When ftp appears in a URL it means that the user is connecting to a file server and not a Web server and that some form of file transfer is going to take place. Most FTP servers require the user to log on to the server in order to transfer files.
In contrast, HTTP is a protocol used to transfer files from a Web server onto a browser in order to view a Web page that is on the Internet. Unlike FTP, where entire files are transferred from one device to another and copied into memory, HTTP only transfers the contents of a web page into a browser for viewing. FTP is a two-way system as files are transferred back and forth between server and workstation. HTTP is a one-way system as files are transported only from the server onto the workstation's browser. When http appears in a URL it means that the user is connecting to a Web server and not a file server. The files are transferred but not downloaded, therefore not copied into the memory of the receiving device.
1.1.5 Proxy Servers
These are intermediary between a network host and other hosts outside the network. Its main functions are to provide enhanced security, manage TCP/IP addresses and speed access to the Internet by providing caching server functions for frequently used documents. In a network setting a proxy server serves as the default gateway for IP communications, this effectively hides the actual IP address from client applications.
Additional services provided by the proxy server:
Caching of web documents: Frequently accessed web pages can be cached
Corporate firewall access: Safe passage for corporate users to the Internet through a firewall allowing protected use of HTTP and FTP.
Filtering client transactions: a proxy can control access to remote web servers and their resources for example a proxy can deny access from a particular computer within a company to a given site.
Transaction logging
Network administrators can track client activity and customize which data to record.
2.0 Database Gateways for web servers
A gateway can be literally defined as a node on a network that serves as an entrance to another network. A database gateway for web servers refers to an “entrance” or connection between a database and a web server.
2.1 Types of Database Gateways for web servers
2.1.1: Common Gateway Interface (CGI)
The common gateway Interface is the earliest, simplest universal database gateway for web servers. In CGI, the web server responds to an HTML form by running or executing a co-process. This co-process is another program that manipulates the data returns the output from the process to CGI interface and the web server then sends the results to the client
The CGI script allows you to create applications that enable transactions between a web server and a database.
Traffic flow when using A CGI program:
1. The web users fills out a form and clicks the submit button
2. Data send to web server calling a CGI program
3. At server in the CGI-BIN directory form data is processed
4. Output generated and return HTML sent to web server
5. Server send output to client browser
Benefits of CGI
Ø CGI are time tested technology, due to this many developers can implement it quickly
Ø Non platform specific
Ø CGI are written in interpreted languages like Perl making then less complex as compared to compiled languages.
CGI drawbacks
1. Create out of process events. An out of process event occurs when an executable program launches a separate process each time it is loaded or referenced.
For example: If one person accesses a CGI script to process an html form, there is an instance of the CGI program loaded into memory. If another person accesses the same CGI script, a separate instance is loaded again. If you were hosting a site with heavy traffic such activities your processor utilization could rise to near 100 % resulting into server being unable to sustain more sections and thereby making your site unavailable
2. CGI scripts are stateless therefore a script must start a new process every time it is accessed even if it is the same user. This results in more processor time. If a script could recognize where and when a session ended it could provide ways to continue at a point where it stopped.
2.1.2 Server Application Programming Interface
To solve the problems presented by CGI, server developers have designed gateways using dynamically loaded object libraries. Rather than being executables as CGI programs are ISAPI applications are implemented ate Dynamic Link Library (DLL) files.
The web server generates the reply document by calling a dynamically loaded subroutine and the returning sub routine’s output to the client. A DLL is a program that can be shared and executed by several applications at once. Once loaded the DLL files can handle requests without being reloaded into memory.
DLL eliminate the substantial overheads involved in starting new processes on the host thus providing better performance.
There are two popular web server SAPIs
Ø Microsoft’s ISAPI
Ø Netscape’s NSAPI
These use proprietary technology meaning that the programs code and functions are tired to a specific vendor. These 2 SAPIs work in basically the same way by using threads or sub processes of the web server thereby not taxing the server’s processor. Another benefit is that you can use these to track client state across requests
Cold fusion
This is a web database gateway marketed by macromedia, originally developed by Allaire Corporation of Cambridge, Mass. (in 2001, Allaire merged with Macromedia) that includes a server and a development toolset designed to integrate databases and Web pages. With Cold Fusion, a user could enter a zip code on a Web page, and the server would query a database for information on the nearest movie theaters and present the results in HTML form. Cold Fusion Web pages include tags written in Cold Fusion Markup Language (CFML) that simplify integration with databases and avoid the use of more complex languages like C++ to create translating programs.
The main advantage of cold fusion is its simplicity; one of the motivations of developing cold fusion was to create an application development environment that could be used by non programmers.
KEI’S Measurements
Shoulder 17
Bust 44
Waist 39
Hip 52
Length of shirt 37
Length of blouse22
ARM 22
ARM 17
Today with the Internet, network services have become more distributed or decentralized, companies and individuals can share resources (mainly information) on a global scale. This global resource sharing is managed by internetworking servers.
1.0 Server implementations:
There are 2 main server operating system software Windows and UNIX. Linux is more like UNIX.
UNIX servers use special programs called daemons, the internet daemon is called inetd, this is used to start other Internet servers. The inetd has a super user access privilege which gives it permission to bind ports to any process it starts.
It is called a daemon because it waits and listens in the background until summoned by another process.
The inetd service runs when the UNIX or Linux system starts up, when the inetd daemon receives a request it launches other services to support the request.
Windows uses services to run internetworking servers. Services are similar to daemons as they wait in the background to be activated. Windows services must be set up by the user with administrator access privileges, which gives the service permission to bind to well known port numbers.
1.1Internetworking servers
1.1.1Web servers\HTTP servers
These send documents for viewing in web browsers. The web browser is a client application that requests documents from the web server, based on the URL that the user enters. The documents that the server sends may be from a disk archive or may be created dynamically when the client requests them.
HTTP servers work closely with the computer’s operating system because a web server is a high performance file sharing system. The performance of an HTTP server therefore depends on how well it works with a particular network operating system.
Access control
An important part of setting up and managing a web server is access control , most websites offer access to the general public; users do not need special permission to access such server resources, this type of access is called anonymous access. Some sites want to restrict access to particular resources, in this case an access control list defines the permissions for a resource by specifying which users and groups have access.
For example the website may offer certain documents only to registered or paying users.
Restricting access to server resources is based on a database of permitted users who must supply a password to access particular server information.
One of the biggest drawbacks of HTTP is that this protocol is stateless implying that: There is no track of the last known or current status of an application or process. As a result the Internet is stateless and each request for a new Web page is processed without any knowledge of previous pages requested.
Because maintaining state is extremely useful, programmers have developed a number of techniques to add state to the World Wide Web. These include server side scripting and client side scripting
1.1.2 Mail Servers
There are two ways to store and access internet email messages. That is:
1: IMAP/SMTP
2: POP3/SMTP
Let’s explain these with a scenario; if you successfully send an email message, the message would be stored in the appropriate server until the recipient downloads it from the server. The POP3 server responds to a request, asks for a password, then transmits the messages to the client.
SMTP stands for simple Mail Transfer Protocol, this protocol a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.
IMAP (Internet Message Access Protocol) and POP (Post Office Protocol) are both protocols for downloading emails from the mail server.
POP3
IMAP
Emails needs to be downloaded into desktop PC before being displayed, you may have the following problems for POP3 access:
You need to download all email again when using another desktop PC to check your email.
May get confused if you need to check email both in the office and at home.
The downloaded email may be deleted from the server depending on the setting of your email client.
Email is kept on server only downloaded when it is opened for display/view, it would gain the following benefits for IMAP access:
No need to download all email when using other desktop PC to check your email.
Easier to identify the unread email.
Outgoing email is stored only locally on the desktop PC.
Outgoing email can be filtered to a mailbox on server for accessibility from other machine.
Messages may be reloaded onto desktop PC several times due to the corruption of system files.
The occurrence of reloading messages from the server to PC is much less when compared to POP3.
Sometimes we attach files to an email these files are supposed to be opened and interpreted by the recipient browser, the attachments are labeled with its MIME type by the sender client application, and the recipient uses the MIME to display the information.
MIME is short for Multipurpose Internet Mail Extensions, a specification for formatting non-ASCII messages so that they can be sent over the Internet. Many e-mail clients nowsupport MIME, which enables them to send and receive graphics, audio, and video files via the Internet mail system. In addition, MIME supports messages in character sets other than ASCII.
In addition to e-mail applications, Web browsers also support various MIME types. This enables the browser to display or output files that are not in HTML format.
1.1.3Streaming Media Servers
Streaming media is designed to emulate traditional broadcast media e.g. radio and television but can provide on demand access to audiences of any size. Streaming media servers use UDP to achieve the effect of a real time broadcast. UDP (User Datagram Protocol) is a connectionless protocol that, like TCP, runs on top of IP networks. Unlike TCP/IP, UDP/IP provides very few error recovery services, offering instead a direct way to send and receive data grams over an IP network. It's used primarily for broadcasting messages over a network.
Unlike other content servers, the client does not receive the entire media file to present the data to the user; instead the client usually discards the streaming media data as it is being presented to the user.
Streaming technologies are becoming increasingly important with the growth of the Internet because most users do not have fast enough access to download large multimedia files quickly. With streaming, the client browser or plug-in can start displaying the data before the entire file has been transmitted.
For streaming to work, the client side receiving the data must be able to collect the data and send it as a steady stream to the application that is processing the data and converting it to sound or pictures. This means that if the streaming client receives the data more quickly than required, it needs to save the excess data in a buffer. If the data doesn't come quickly enough, however, the presentation of the data will not be smooth.
There are a number of competing streaming technologies emerging. For audio data on the Internet, the de facto standard is Progressive Network's RealAudio
Streaming media servers are well suited for intranet. Businesses and other organizations can use streaming media and corporate networks to distribute audio and video material, including employee meetings, training films and marketing material.
1.1.4 FTP Servers
Short for File Transfer Protocol, the protocol for exchanging files over the Internet. FTP works in the same way as HTTP for transferring Web pages from a server to a user's browser and SMTP for transferring electronic mail across the Internet in that, like these technologies, FTP uses the Internet's TCP/IP protocols to enable data transfer.
FTP is most commonly used to download a file from a server using the Internet or to upload a file to a server (e.g., uploading a Web page file to a server
When ftp appears in a URL it means that the user is connecting to a file server and not a Web server and that some form of file transfer is going to take place. Most FTP servers require the user to log on to the server in order to transfer files.
In contrast, HTTP is a protocol used to transfer files from a Web server onto a browser in order to view a Web page that is on the Internet. Unlike FTP, where entire files are transferred from one device to another and copied into memory, HTTP only transfers the contents of a web page into a browser for viewing. FTP is a two-way system as files are transferred back and forth between server and workstation. HTTP is a one-way system as files are transported only from the server onto the workstation's browser. When http appears in a URL it means that the user is connecting to a Web server and not a file server. The files are transferred but not downloaded, therefore not copied into the memory of the receiving device.
1.1.5 Proxy Servers
These are intermediary between a network host and other hosts outside the network. Its main functions are to provide enhanced security, manage TCP/IP addresses and speed access to the Internet by providing caching server functions for frequently used documents. In a network setting a proxy server serves as the default gateway for IP communications, this effectively hides the actual IP address from client applications.
Additional services provided by the proxy server:
Caching of web documents: Frequently accessed web pages can be cached
Corporate firewall access: Safe passage for corporate users to the Internet through a firewall allowing protected use of HTTP and FTP.
Filtering client transactions: a proxy can control access to remote web servers and their resources for example a proxy can deny access from a particular computer within a company to a given site.
Transaction logging
Network administrators can track client activity and customize which data to record.
2.0 Database Gateways for web servers
A gateway can be literally defined as a node on a network that serves as an entrance to another network. A database gateway for web servers refers to an “entrance” or connection between a database and a web server.
2.1 Types of Database Gateways for web servers
2.1.1: Common Gateway Interface (CGI)
The common gateway Interface is the earliest, simplest universal database gateway for web servers. In CGI, the web server responds to an HTML form by running or executing a co-process. This co-process is another program that manipulates the data returns the output from the process to CGI interface and the web server then sends the results to the client
The CGI script allows you to create applications that enable transactions between a web server and a database.
Traffic flow when using A CGI program:
1. The web users fills out a form and clicks the submit button
2. Data send to web server calling a CGI program
3. At server in the CGI-BIN directory form data is processed
4. Output generated and return HTML sent to web server
5. Server send output to client browser
Benefits of CGI
Ø CGI are time tested technology, due to this many developers can implement it quickly
Ø Non platform specific
Ø CGI are written in interpreted languages like Perl making then less complex as compared to compiled languages.
CGI drawbacks
1. Create out of process events. An out of process event occurs when an executable program launches a separate process each time it is loaded or referenced.
For example: If one person accesses a CGI script to process an html form, there is an instance of the CGI program loaded into memory. If another person accesses the same CGI script, a separate instance is loaded again. If you were hosting a site with heavy traffic such activities your processor utilization could rise to near 100 % resulting into server being unable to sustain more sections and thereby making your site unavailable
2. CGI scripts are stateless therefore a script must start a new process every time it is accessed even if it is the same user. This results in more processor time. If a script could recognize where and when a session ended it could provide ways to continue at a point where it stopped.
2.1.2 Server Application Programming Interface
To solve the problems presented by CGI, server developers have designed gateways using dynamically loaded object libraries. Rather than being executables as CGI programs are ISAPI applications are implemented ate Dynamic Link Library (DLL) files.
The web server generates the reply document by calling a dynamically loaded subroutine and the returning sub routine’s output to the client. A DLL is a program that can be shared and executed by several applications at once. Once loaded the DLL files can handle requests without being reloaded into memory.
DLL eliminate the substantial overheads involved in starting new processes on the host thus providing better performance.
There are two popular web server SAPIs
Ø Microsoft’s ISAPI
Ø Netscape’s NSAPI
These use proprietary technology meaning that the programs code and functions are tired to a specific vendor. These 2 SAPIs work in basically the same way by using threads or sub processes of the web server thereby not taxing the server’s processor. Another benefit is that you can use these to track client state across requests
Cold fusion
This is a web database gateway marketed by macromedia, originally developed by Allaire Corporation of Cambridge, Mass. (in 2001, Allaire merged with Macromedia) that includes a server and a development toolset designed to integrate databases and Web pages. With Cold Fusion, a user could enter a zip code on a Web page, and the server would query a database for information on the nearest movie theaters and present the results in HTML form. Cold Fusion Web pages include tags written in Cold Fusion Markup Language (CFML) that simplify integration with databases and avoid the use of more complex languages like C++ to create translating programs.
The main advantage of cold fusion is its simplicity; one of the motivations of developing cold fusion was to create an application development environment that could be used by non programmers.
KEI’S Measurements
Shoulder 17
Bust 44
Waist 39
Hip 52
Length of shirt 37
Length of blouse22
ARM 22
ARM 17
posted by mwesigye herbert at 4:05 AM
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