BASIC TAGS OF HTML


Let us now look at tags in more detail. A <TAG> tells the browser to do something. An ATTRIBUTE goes inside the <TAG> and tells the browser how to do it. A tag can have several attributes. Tags can also have default attributes. The default value is a value that the browser assumes if you have not told it otherwise. A good example is the font size. The default font size is 3. If you say nothing the size attribute of the font tag will be taken to have the value 3.
Consider the example shown in Fig.1A. Type the code specified in the figure in a text editor such as notepad and save it as “fig1A.html”. To render the file and see your page you can choose one of two ways:

  1. Find the icon of the html file you  just made (fig1A.htm) and double click on it. Or,
  2. In Internet Explorer, click on File/Open File and point to the file (fig 1A.htm).


Figure 1A. A Simple Web Page


HTML Tag

As shown in Figure 1A above, <HTML> is a starting tag. To delimit the text inside, add a closing tag by adding a “/” to the starting tag. Most but not all tags have a closing tag. It is necessary to write the code for an HTML page between <HTML> and </HTML>. Think of tags as talking to the browser or, better still, giving it instructions. What you have just told the browser is 'this is the start of an HTML document' (<HTML>) and 'this is the end of an HTML document' (</HTML>). Now you need to put some matter in between these two markers. Every HTML document is segregated into a HEAD and BODY. The information about the document is kept within <HEAD> tag. The BODY contains the page content.

TITLE Tag

The only thing you have to concern yourselves with in the HEAD tag (for now) is the TITLE tag. The bulk of the page will be within the BODY tag, as shown in Figure.1A.

<HEAD>
<TITLE> MY WEB </TITLE>
</HEAD>

Here the document has been given the title my web. It is a good practice to give a title to the document created. What you have made here is a skeleton HTML document. This is the minimum required information for a web document and all web documents should contain these basic components. Secondly, the document title is what appears at the very top of the browser window.


BODY Tag

If you have a head, you need a body. All the content to be displayed on the web page has to be written within the body tag. So whether text, headlines, text-box, check-box or any other possible content, everything to be displayed must be kept within the BODY tag as shown in Figure 1A. Whenever you make a change to your document, just save it and hit the Reload/Refresh button on your browser. In some instances just hitting the Reload/Refresh button doesn’t quite work. In that case hit Reload/Refresh while holding down the SHIFT key.

The BODY tag has following attributes:
  • BGCOLOR: It can be used for changing the background color of the page. By default the background color is white.
  • BACKGROUND: It is used for specifying the image to be displayed in the background of the page.
  • LINK: It indicates the color of the hyperlinks, which have not been visited or clicked on.
  • ALINK: It indicates the color of the active hyperlink. An active link is the one on which the mouse button is pressed.
  • VLINK: It indicates the color of the hyperlinks after the mouse is clicked on it.
  • TEXT: It is used for specifying the color of the text displayed on the page.


Consider the following example:
Figure 1B. A Page with a Background Color





The values specified for BGCOLOR and TEXT tags indicate the color of the background of the page and that of the text respectively. These are specified in hexadecimal format. The range of allowable values in this format is from “#000000” to “#FFFFFF”. The“#” symbol has to precede the value of the color so as to indicate to the browser that has to be interpreted as a hexadecimal value. In this six digit value, the first two digits specify the concentration of the color red, the next two digits specify the concentration of the color green and the last two digits specify the concentration of the color blue. So the value is a combination of the primary colors red, green and blue and that is why it is called RGB color. If we specify the value “#FF0000”, the color appears to be red.”#000000” gives black and “#FFFFFF” gives the color white. You also have the option of specifying the color by giving its name, like: <BODY TEXT = “WHITE”>. You can also specify a background image instead. (Note that the image should be in the same folder as your HTML file. More on this below).
Try it out with the example HTML below:


Figure 1C. A Page with an Image in the Background


Posted on Wednesday, December 11, 2013 by Unknown

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INTRODUCTION TO HTML


You would by now have been introduced to the Internet and the World Wide Web (often just called the Web) and how it has changed our lives. Today we have access to a wide variety of information through Web sites on the Internet. We can access a Web site if we have a connection to the Internet and a browser on our computer. Popular browsers are Microsoft Internet Explorer, Netscape Navigator and Opera. When you connect to a Web site, your browser is presented with a file in a special format by the Web server on the remote computer. The contents of the file are stored in a special format using Hyper Text Markup Language, often called HTML This format is rendered, or interpreted, by the browser and you then see the page of the web site from your computer. HTML is one language in a class of markup languages, the most general form of which is Standard Generalized Markup Language, or SGML. Since SGML is complex, HTML was invented as a simple way of creating web pages that could be easily accessed by browsers.

HTML is a special case of SGML. HTML consists of tags and data. The tags serve to define what kind of data follows them, thereby enabling the browser to render the data in the appropriate form for the user to see. There are many tags in HTML, of which the few most important ones are introduced in this unit. HTML files usually have the extension “.htm” or “.html”. If you want to create Web pages, you need a tool to write the HTML code for the page.  This can be a simple text editor if you are hand-coding HTML. You also have sophisticated HTML editors available that automate many (though not all) of the tasks of coding HTML. You also need a browser to be able to render your code so that you can see the results.


WHAT IS HTML?

As indicated earlier, HTML stands for Hypertext Markup Language. HTML provides a way of displaying Web pages with text and images or multimedia content. HTML is not a programming language, but a markup language. An HTML file is a text file containing small markup tags. The markup tags tell the Web browser, such as Internet Explorer or Netscape Navigator, how to display the page. An HTML file must have an htm or html file extension. These files are stored on the web server. So if you want to see the web page of a company, you should enter the URL (Uniform Resource Locator), which is the web site address of the company in the address bar of the browser. This sends a request to the web server, which in turn responds by returning the desired web page.  The browser then renders the web page and you see it on your computer.

HTML allows Web page publishers to create complex pages of text and images that can be viewed by anyone on the Web, regardless of what kind of computer or browser is being used. Despite what you might have heard, you don’t need any special software to create an HTML page; all you need is a word processor (such as Microsoft Word) and a working knowledge of HTML. Fortunately, the basics of HTML are easy to master.  However, you can greatly relieve tedium and improve your productivity by using a good tool.  A simple tool is Microsoft FrontPage that reduces the need to remember and type in HTML tags.  Still, there can always be situations where you are forced to hand code certain parts of the web page. HTML is just a series of tags that are integrated into a document that can have text, images or multimedia content. HTML tags are usually English words (such as block quote) or abbreviations (such as p for paragraph), but they are distinguished from the regular text because they are placed in small angle brackets. So the paragraph tag is <p>, and the block quote tag is <blockquote>. Some tags dictate how the page will be formatted (for instance, <p> begins a new paragraph), and others dictate how the words appear (<b> makes text bold). Still others provide information - such as the title - that doesn’t appear on the page itself. The first thing to remember about tags is that they travel in pairs. Most of the time that you use a tag - say <blockquote> - you must also close it with another tag - in this case, </blockquote>. Note the slash - / - before the word “blockquote”; that is what distinguishes a closing tag from an opening tag.

The basic HTML page begins with the tag <html> and ends with </html>. In between, the file has two sections -the header and the body.  The header - enclosed by the <head> and </head> tags -contains information about a page that will not appear on the page itself, such as the title. The body - enclosed by <body> and </body> - is where the action is. Everything that appears on the page is contained within these tags.

HTML pages are of two types:
  • Static
  • Dynamic

Static Pages

Static pages, as the name indicates, comprise static content (text or images). So you can only see the contents of a web page without being able to have any interaction with it.

Dynamic Pages

Dynamic pages are those where the content of the web page depend on user input. So interaction with the user is required in order to display the web page. For example, consider a web page which requires a number to be entered from the user in order to find out if it is even or odd. When the user enters the number and clicks on the appropriate button, the number is sent to the web server, which in turn returns the result to the user in an HTML page.

Posted on Tuesday, December 10, 2013 by Unknown

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INTERNET TOOLS


In this article, we will look at two software tools available on the Internet.

Search Engines


Search Engines are programs that search the web. Web is a big graph with the pages being the nodes and hyperlinks being the arcs. Search engines collect all the hyperlinks on each page they read, remove all the ones that have already been processed and save the rest. The Web is then searched breadth-first, i.e. each link on page is followed and all the hyperlinks on all the pages pointed to are collected but they are not traced in the order obtained.

Automated search is the service that is provided by Search engines. An automated search service allows an individual to find information that resides on remote computers. Automated search systems use computer programs to find web pages that contain information related to a given topic. It allows to locate:
 
  • Web pages associated with a particular company or individual
  • Web pages that contain information about a particular product.
  • Web pages that contain information about a particular topic.

The results of an automated search can be used immediately or stored in a file on disk to use it later. The results of a search are returned in the form of a web page that has a link to each of the items that was found. Automated search is helpful when a user wants to explore a new topic. The automated search produces a list of candidate pages that may contain information. The user reviews each page in the list to see whether the contents are related to topic or not. If so, the user records the location or if not user moves on to the page in the list. Search mechanisms uses a similar method of search as in the telephone book i.e. before any user invoke the search mechanism a computer program contacts computers on the Internet, gathers a list of available information, sorts the list and then stores the result on a local disk on the computer that runs a search server. When a user invokes a search, the user client program that contacts the server. The client sends a request that contains the name the user entered. When the request arrives at the server, it consults the list of file names on its local disk and provides the result.

Web Browser


A Web browser is software program that allows you to easily display Web pages and navigate the Web. The first graphical browser, Mosaic, was developed in Illinois at the National Center for Supercomputing Applications (NCSA). Each browser displays Web-formatted documents a little differently. As with all commercial software, every program has its own special features.

The two basic categories of Web browser are:

  • Text-only browsers: A text-only browser such as Lynx allows you to view Web pages without showing art or page structure. Essentially, you look at ASCII text on a screen. The advantage of a text-only browser is that it displays Web pages very fast. There's no waiting for multimedia downloads.
  • Graphical browsers: To enjoy the multimedia aspect of the Web, you must use a graphical browser such as Netscape Navigator or NCSA Mosaic. Graphical browsers can show pictures, play sounds, and even run video clips. The drawback is that multimedia files, particularly graphics, often take a long time to download. Graphical browsers tend to be significantly slower than their text-only counterparts. And this waiting time can be stretched even further with slow connections or heavy online traffic. 

Many different browsers are available for exploring the Internet. The two most popular browsers are Netscape Navigator and Microsoft Internet Explorer. Both of these are graphical browsers, which mean that they can display graphics as well as text.

SUMMARY


I hope now you have an idea in the basic concepts about an Internet. Internet is a network of networks where lot of information is available and is meant to be utilized by you. No one owns the Internet. It consists of a large number of interconnected autonomous networks that connect millions of computers across the world. The unit describes the various tools available on the Internet and the various services provided by the Internet to users. In this unit we have talked about the Electronic mail Usenet and newsgroups, FTP, Telnet and search engines. We also describe the use of frequently asked questions. The unit also describes the importance of Internet addresses. Addresses are essential for virtually everything we do on the Internet. There are many services available on the Internet for document retrieval. For browsing the Internet there are many browsers available such as Gopher and World Wide Web. Both of these browsers are easy to use and most popular browsing mechanisms on the Internet.

Posted on Thursday, December 05, 2013 by Unknown

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PROTOCOLS AND SERVICES ON INTERNET


To work with Internet and to utilize its facilities we use certain tools. For example,Telnet is a tool, which is utilized for logging on remote computers on the Internet. Let us briefly discuss about some of the important tools and services.

Domain Name System


Domain name is a name given to a network for ease of reference. Domain refers to a group of computers that are known by a single common name. Somebody has to transfer these domain names into IP addresses. It is decided on the physical location of the web server as well as where the domain name is registered. Some generic domain names are:

Domain name Description
com Commercial Organization
Edu Educational Organization
Gov Government Organization


Thus, humans use domain names when referring to computers on the Internet, whereas computers work only with IP addresses, which are numeric. DNS was developed as a distributed database. The database contains the mappings between the domain names and IP addresses scattered across different computers. This DNS was consulted whenever any message is to be sent to any computer on the Internet. DNS is based on the creation of the hierarchical domain based naming architecture, which is implemented as a distributed database. It is used for mapping host names and email addresses to IP addresses. Each organization operates a domain name server that contains the list of all computers in that organization along with their IP addresses. When an application program needs to translate a computer’s name into the computer’s IP address, the application becomes a client of the DNS. It contacts a domain name server and sends the server an alphabetic computer name then the server returns the correct IP address. The domain name system works like a directory. A given server does not store the names and addresses of all possible computers in the Internet. Each server stores the name of the computers at only one company or enterprise.

SMTP and Electronic Mail


One of the very useful things about Internet is that it allows you almost instantly exchange of electronic message (e-mail) across the worlds. E-mail is a popular way of communication on the electronic frontier. You can E-mail to your friend or a researcher or anybody for getting a copy of a selected paper. Electronic mail system provides services that allowed complex communication and interaction. E-mail provide the following facilities:
  • Composing and sending/receiving a message.
  • Storing/forwarding/deleting/replying to a message.
  • Sending a single message to more than one person.
  • Sending text, voice, graphics and video.
  • Sending a message that interacts with other computer programs.

Another commonly used Internet service is electronic mail. E-mail uses an application level protocol called Simple Mail Transfer Protocol or SMTP. SMTP is also a text-based protocol, but unlike HTTP, SMTP is connection oriented. SMTP is also more complicated than HTTP.

When you open your mail client to read your e-mail, this is what typically happens:
  1. The mail client (Netscape Mail, Lotus Notes, Microsoft Outlook, etc.) opens a connection to it's default mail server. The mail server's IP address or domain name is typically setup when the mail client is installed.
  2. The mail server will always transmit the first message to identify itself.
  3. The client will send an SMTP HELO command to which the server will respond with a 250 OK message.
  4. Depending on whether the client is checking mail, sending mail, etc. the appropriate SMTP commands will be sent to the server, which will respond accordingly.
  5. This request/response transaction will continue until the client sends an SMTP QUIT command.The server will then say goodbye and the connection will be closed.

Similarly, when you send an e-mail message your computer sends it to an SMTP server. The server forwards it to the recipients mail server depending on the email address. The received message is stored at the destination mail server until the addressee retrieves it. To receive E-mail a user Internet account includes an electronic mailbox. A message sent for you is received at your Internet host computer, where it is stored in your electronic mailbox. As soon as you login into your Internet account, one of the first things you should do is to check your mailbox.

E-mail system follows the client-server approach to transfer messages across the Internet. When a user sends an E-mail message a program on the sender’s computer becomes a client. It contacts an e-mail server program on the recipient’s computer and transfers a copy of the message. Some of the mail programs those exist on Internet are UCB mail, Elm, Pine etc. However, one thing, which you must emphasize while selecting a mail program, is the user friendliness of that program. Through E-mail on Internet you can be in direct touch of your friend and colleagues.

Mailing lists on Internet

Another exciting aspect about the E-mail is that you can find groups of people who share your interests-whether you are inclined toward research, games or astronomy. E-mail provides a mechanism for groups of people who have shared interests to establish and maintain contact. Such interest groups are referred to as mailing lists (lists for short). After all they are mailing lists of the members e-mail addresses. You can subscribe to any of such lists. You will receive copies of all the mail sent to the list. You can also send mail to al subscribers of the list.

Http and World Wide Web


One of the most commonly used services on the Internet is the World Wide Web (WWW). The application protocol that makes the web work is Hypertext Transfer Protocol or HTTP. Do not confuse this with the Hypertext Markup Language (HTML). HTML is the language used to write web pages. HTTP is the protocol that web browsers and web servers use to communicate with each other over the Internet. It is an application level protocol because it sits on top of the TCP layer in the protocol stack and is used by specific applications to talk to one another. In this case the applications are web browsers and web servers.

HTTP is a connectionless text based protocol. Clients (web browsers) send requests to web servers for web elements such as web pages and images. After the request is serviced by a server, the connection between client and server across the Internet is disconnected. A new connection must be made for each request. Most protocols are connection oriented. This means that the two computers communicating with each other keep the connection open over the Internet. HTTP does not however. Before an HTTP request can be made by a client, a new connection must be made to the server.

When you type a URL into a web browser, this is what happens:

  1. If the URL contains a domain name, the browser first connects to a domain name server and retrieves the corresponding IP address for the web server.
  2. The web browser connects to the web server and sends an HTTP request (via the protocol stack) for the desired web page.
  3. The web server receives the request and checks for the desired page. If the page exists, the web server sends it. If the server cannot find the requested page, it will send an HTTP 404 error message. (404 means 'Page Not Found' as anyone who has surfed the web probably knows.)
  4. The web browser receives the page back and the connection is closed. 
  5. The browser then parses through the page and looks for other page elements it needs to complete the web page. These usually include images, applets, etc.
  6. For each element needed, the browser makes additional connections and HTTP requests to the server for each element.
  7. When the browser has finished loading all images, applets, etc. the page will be completely loaded in the browser window.  

Most Internet protocols are specified by Internet documents known as a Request For Comments or RFCs. RFCs may be found at several locations on the Internet.

WWW is an Internet navigation tool that helps you to find and retrieve information links to other WWW pages. The WWW is a distributed hypermedia environment consisting of documents from around the world. The documents are linked using a system known as hypertext, where elements of one document may be linked to specific elements of another document. The documents may be located on any computer connected to the Internet. The word “document” is not limited to text but may include video, graphics, databases and a host of other tools.

The World Wide Web is described as a “wide area hypermedia information initiative among to give universal access to large universe of documents”. World Wide Web provides users on computer networks with a consistent means to access a variety of media in a simplified fashion. A popular software program to search the Web is called Mosaic, the Web project has modified the way people view and create information. It has created the first global hypermedia network.

Once again the WWW provides an integrated view of the Internet using clients and servers. As discussed earlier, clients are programs that help you seek out information while servers are the programs that find information to the clients. WWW servers are placed all around the Internet.

The operations of the Web mainly rely on hypertext as its means of interacting with users. But what is hypertext? Hypertext as such is the same as regular text that is it can be written, read, searched or edited; however, hypertext contains connections within the text to other documents. The hypertext links are called hyperlinks. These hyperlinks can create a complex virtual web of connections.

Hypermedia is an advanced version of hypertext documents as it contains links not only to other pieces of text but also to other forms of media such as sounds, images and movies. Hypermedia combines hypertext and multimedia.

Usenet and Newsgroups


In Internet there exists another way to meet people and share information. One such way is through Usenet newsgroups. These are special groups set up by people who want to share common interests ranging from current topics to cultural heritages. These are currently thousands of Usenet newsgroups.

The Usenet can be considered as another global network of computers and people, which is interwined with the Internet. However, Usenet does not operate interactively like the Internet, instead Usenet machines store the messages sent by users. Unlike mail from mailing lists, the news articles do not automatically fill your electronic mailbox. For accessing the information on newsnet, one needs a special type of program called a newsreader. This program help in retrieving only the news you want from Usenet storage site and display it on your terminal. Usenet is like living thing, New newsgroups gets added, the groups which have too much traffic get broken up into smaller specialized groups, the groups even can dissolve themselves. However, all of this occurs based on some commonly accepted rules and by voting. For Usenet, there is no enforcement body; it entirely depends on the cooperation of its computers owners and users.
The newsgroups are really meant fro interaction of people who share your interests. You can post your own questions as well as your answers to the questions of others, on the Usenet. One thing, which is worth mentioning here, is that when one is interacting wit people on Internet certain mannerism should be adopted. These rules are sometimes called “netiquette”. In a face-to-face conversation you can always see a person’s facial gestures and hand movements and can ascertain whether he is teasing or is being sarcastic or sometimes even lying. However, in on-line interaction one cannot see the person one is interacting with. The rules of netiquette may help to compensate some of these limitations of this on-line environment.

File Transfer Protocol (FTP)


FTP (File Transfer Protocol), a standard Internet protocol, is the simplest way to exchange files between computers on the Internet. Like the Hypertext Transfer Protocol (Hypertext Transfer Protocol), which transfers displayable Web pages and related files, FTP is an application protocol that uses the Internet's TCP/IP protocols. FTP is commonly used to transfer Web page files from their creator to the computer that acts as their server for everyone on the Internet. It's also commonly used to downloading programs and other files to the computer from other servers. However, for such transfer you need an account name on a host and the password. The FTP program will make connection with the remote host, which will help you to browse its directories and mark files for transfer. However, you cannot look at the contents of a file while you are connected via FTP. You have to transfer the copy and then look at it once it is on your own account.

FTP includes many commands but only few are used to retrieve a file. A user needs to understand the three basic commands to connect to remote computer, retrieve a copy of file and exit the FTP program. The commands with their meanings are:

Command Purpose
Open connect to a remote computer
get retrieve a file from the computer
bye terminate the connection and leave the FTP program


Transferring a file via FTP requires two participants: an FTP client program and FTP server program. The FTP client is the program that we run on our computers. The FTP server is the program that runs on the huge mainframe somewhere and stores tens thousands of files. It is similar to an online library of files. The FTP client can download (receive) or upload (send) files to the FTP server. Using Web browser you can download the files but you can not upload the files. FTP applications will help you to upload the files to the web sites, which you are maintaining.

FTP only understands two basic file formats. It classifies each file either as a text file or a binary file. A text file contains a sequence of characters collected into lines. Although computers used ASCII encoding for text files, FTP includes commands to translate between ASCII and other character encoding. FTP uses the classification binary file for all nontext files. The user must specify binary for any file that contains:
  • A computer program
  • Audio data
  • A graphic or video image
  • A spreadsheet
  • A document from a word processor
  • A compressed file

FTP service compress files to reduce the total amount of disk space the files require. Before transferring a file user must tell FTP that the file contains ASCII text or nontext file. FTP assumes to perform ASCII transfers unless the user enters the binary command.

There are many FTP programs that you can download from the Internet. Windows has its own command line based FTP program. To execute it, select Run from Windows taskbar and type FTP and press enter. By typing open command you can connect to any ftp server. To connect to FTP server you must have a login name and the password. Most of the FTP servers allow anonymous connections. In this case username is anonymous and password is your e-mail address.

Another important FTP program, which is available as a shareware, is WSFTP. Using this window based program it is easier to maintain your web site.

Telnet

TELNET stands for TErminal NETwork. Telnet is both a TCP/IP application and a protocol for connecting a local computer to a remote computer. Telnet is a program that allows an Internet host computer to become a terminal of another host on the Internet. Telnet is the Internet remote login service. Telnet protocol specifies exactly how a remote login interacts. The standard specifies how to client contacts the server and how the server encodes output for transmission to the client. To use the Telnet service, one must invoke the local application program and specify a remote machine. The local program becomes a client, which forms a connection to a server on the remote computer. The client passes keystrokes and mouse movements to the remote machine and displays output from the remote machine on the user’s display screen. Telnet provides direct access to various services on Internet. Some of these services are available on your host, but Telnet is especially useful when these services are not available on your host. For example, if you want to use graphical interfaces designed by other users then Telnet, allows you to access their hosts and use their new interfaces. Similarly, whenever someone creates a useful service on his host, Telnet allows you to access this valuable information resource. This tools Is especially useful for accessing public services such as library card catalogues, the kind of databases available on the machine etc. You can also log into any catalogue service of a library and use it.
The working of TELNET,
  • The commands and characters are sent to the operating system on the common server computer.
  • The local operating system sends these commands and characters to a TELNET client program, which is located on the same local computer.
  • The TELNET client transforms the characters entered by the user to an agreed format known as Network Virtual Terminal (NVT) characters and sends them to the TCP/IP protocol stack of the server computer. NVT is the common device between the client and server.
  • The commands and text are first broken into TCP and then IP packets and are sent across the physical medium from the local client computer to the server.
  • At the server computer’s end, the TCP/IP software collects all the IP packets, verifies their correctness and reconstructs the original command and handover the commands or text to that computer operating system.
  • The operating system of the server computer hands over these commands or text to the TELNET server program, which is executing on that remote computer.
  • The TELNET server program on the remote server computer then transforms the commands or text from the NVT format to the format understood by the remote computer.
  • The TELNET cannot directly handover the commands or text to the operating system so TELNET hands over the commands/text to the Psuedo-terminal driver.

The Pseudo-terminal driver program then hands over the commands or text to the operating system of the remote computer, which then invokes the application program on the remote server.
 
There are many databases available on the Internet. You can explore these databases using Telnet. There are going to be many Internet services yet to be created. Every year and better means of accessing the treasures of the Internet is appearing in which Telnet is the key for accessing.

Posted on Thursday, December 05, 2013 by Unknown

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