Introduction to Web Pages

CHAPTER 1 INTRODUCTION TO WEB PAGES  The Internet 2  Internet is a large number of computers connected together to share information.  It is a collection of networks (a network of networks) sharing digital information via a c...

CHAPTER 1 INTRODUCTION TO WEB PAGES  The Internet 2  Internet is a large number of computers connected together to share information.  It is a collection of networks (a network of networks) sharing digital information via a common set of networking and software protocols.  It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked together.  Nearly anyone can connect their computer to the Internet and immediately communicate with other computers and users on the network.  The Internet has become an industry in its own respect.  The Internet… 3  The Internet began in the late 1960s as an experiment in the design of robust computer networks.  The goal was to construct a network of computers that could withstand the loss of several machines without compromising the ability of the remaining ones to communicate.  Funding came from the U.S. Department of Defense, which had a vested interest in building information networks that could withstand nuclear attack.  The result was a network called ARPANET developed by Advanced Research Projects Agency (ARPA) of the United States Department of Defense.  Later ARPANET was replaced by National Science Foundation Network (NSFNET) accessible to research and education organization in 1990s.  NSFNET was finally commercialized in 1995.  The Internet… 4  The Internet, as a “network of networks”, consists of many computers, called servers or hosts, which are linked by communication lines.  These hosts are located in different part of the world and connect millions of people.  The administrators of these hosts may make information or software stored on them publically available, so that others can view, download or use the data.  Another important thing that has contributed for growth of Internet is ownership.  Until now, nobody owns the Internet.  Its unique design transformed it into a source for innovation that anyone in the world could use.  However, its backbone: servers and Internet Service Providers (ISP) are owned by private as well government organizations.  The Internet… 5 Figure The growth of Internet  The Internet… 6  The Internet has, in a short space of time, become fundamental to the global economy.  More than a billion people worldwide use it, both at work and in their social lives.  Generally, the services of internet are:  World Wide Web (WWW)  Electronic mail  File Transfer (ftp)  Discussion Groups  Usenet (News Group)  Internet Chat  Search Services  World Wide Web 7  World Wide Web (WWW) is a collection of interconnected documents and other resources linked by hyperlinks.  Hyperlink is also called hypertext or simply link  Hyperlinks are reference or navigation element in a document to another document.  WWW is a massive storehouse of information that resides on internet.  WWW was created by Tim Berners-Lee in 1989 at the European Nuclear Research Center (CERN) in Switzerland.  World Wide Web... 8  Berners-Lee created WWW by bringing together three technologies that were already in development at the time:  Markup Language – a system of instructions and formatting codes embedded in text.  Hypertext – a means of embedding links to other documents, images, and other elements in a document.  Internet – a global network of computers where clients request service and servers provide services  WWW pages are connected to one another using hypertext that allows you to move from any page to any other page, and to graphics, multimedia files, as well as any Internet resources.  World Wide Web... 9 Fig WWW pages and how they are interlinked  World Wide Web... 10  The Web consists of many millions of internet-connected servers, each with information on them to share.  These documents can be formed of anything from plain text to multimedia or even 3D objects.  The computers on which the information is stored, called servers  Server deliver this information over the Internet to client computers using a protocol.  The protocol just provides a mechanism that allows a client to request a document, and a server to send that document.  World Wide Web... 11  The goal of a web server is to serve information to anyone who requests it; the web pages stored on the server are made publically available.  WWW is a client/server architecture where client machines request service from server machines.  In client/server architecture, some application program act as information provider(server), while other application act as information receiver(client).  The backbone of the web is the network of web servers across the world.  These are really just computers that have a particular type of software running on them: web server  The web server software knows how to speak the protocol and knows which information stored on the computer should be made accessible through the web.  World Wide Web... 12 Figure 1.2 How WWW works: retrieving a web page from server by clients  Designing a good website 13  Know your audience and have a clear goal for your Web site..  Steps to a well designed Web site  Have a goal  Target your audience  Create a plan  Select a Web service provider  Try it out  Maintain it  Characteristics of a good web site  Well-organized  Easy to navigate  Attractive  Useful  Up-to-date  Be easy to read.  Hypertext Transfer Protocol(HTTP) 14  Web clients interact with web servers with a simple application-level protocol called HTTP.  HTTP runs on top of TCP/IP network connections.  HTTP is the standard protocol for transferring web content.  It is the foundation of data communication for the World Wide Web.  HTTP has been in use by the World Wide Web global information initiative since 1990.  The first version of HTTP, referred to as HTTP/0.9, was a simple protocol for raw data transfer across the Internet.  HTTP… 15  HTTP/1.0, as defined by RFC (Request For Comments), improved the protocol by allowing messages to be in the format of Multipurpose Internet Mail Extension (MIME) like messages, containing meta-information about the data transferred and modifiers on the request/response semantics.  While HTTP/1.0 has provided with many capabilities it does not take in to consideration the need for persistent connections, or virtual hosts.  This has necessitated a protocol version change.  This specification defines the protocol referred to as HTTP/1.1.  This protocol includes more strict requirements than HTTP/1.0 in order to ensure reliable implementation of its features.  HTTP… 16  The HTTP protocol is a request/response protocol.  A client sends a request to the server in the form of a request method, URI, and protocol version, followed by possible body content over a connection with a server.  HTTP request methods indicate the desired action to be performed on the identified resource.  The most commonly used methods are:  Delete – to delete some resource on the server  GET -The GET method means retrieve whatever information is identified by the Request-URI.  When a client issues a GET request, it is asking the server for something.  HEAD - The HEAD method is identical to GET except that the server must not return a message-body in the response.  When a client issues a HEAD request it typically is looking to receive the response status code (e.g 200, etc..) only and not the actual body content.  Request contain two parts, header which contain metadata and additional information and body which contain file.the body may be empty if the client do not send data to the server.  The is true for response except that no body cannot be empty.  HTTP… 17  POST - The POST method is used to request that the origin server accept the entity enclosed in the request as a new subordinate of the resource identified by the Request-URI in the Request-Line.  In simple terms, when a client issues a POST request it is sending data to the server (e.g.. uploading a file, submitting user information, credit card data, etc).  The server responds with a status line, including the message’s protocol version and a success or error code, followed by a MIME like message containing server information, entity meta-information, and possible entity body content.  Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on web server  Trace request server send echoes to the client  Option the server accept certain resource  HTTP… 18  Generally, the HTTP request line includes HTTP version, request method and request URL  the response line include HTTP version, status code(a three digit number) and status description which has textual explanation for the status code.  HTTP… 19 HTTP request line HTTP response line HTTP Version (eg. HTTP/1.1, HTTP Version (eg. HTTP/1.1, HTTP/1.0) HTTP/1.0) Request method (e.g. GET, Status code (e.g. 100, 200) POST, DELETE, TRACE, PATCH) Request URL Status Description (e.g. Ok and Success (description for status code 100 and 200 respectively) Table Summary of the structure of HTTP  HTTP… 20 HTTP Status Codes  In HTTP/1.0 and later versions, the first line of the HTTP response is called the status line.  It includes a numeric status code (such as 404) and a textual reason phrase (such as "Not Found").  The way the user agent handles the response primarily depends on the code and secondarily on the response headers.  The first digit of the status code specifies one of five classes of response: Informational, success, redirection, client error, server error.  It is the bare minimum that an HTTP client should recognizes these five classes.  The phrases used are the standard examples, but any human-readable alternative can be provided.  HTTP… 21 Example Status codes: 100 Continue The client should continue with its request. 200 OK The request has succeeded. The information returned with the response is dependent on the method used in the request. 301 Moved The requested resource has been assigned a new Permanentl permanent URI and any future references to this y resource SHOULD use one of the returned URIs. 404 Not Found The server has not found anything matching the Request-URI. 500 Internal The server encountered an unexpected condition Server which prevented it from fulfilling the request. Error  HTTP… 22 1xx: Information Message: Description: 100 Continue Only a part of the request has been received by the server, but as long as it has not been rejected, the client should continue with the request 101 Switching Protocols The server switches protocol  HTTP… 23 2xx: Successful Message: Description: 200 OK The request is OK 201 Created The request is complete, and a new resource is created 202 Accepted The request is accepted for processing, but the processing is not complete 203 Non-authoritative Information 204 No Content 205 Reset Content 206 Partial Content  HTTP… 24 3xx: Redirection Message: Description: 300 Multiple Choices A link list. The user can select a link and go to that location. Maximum five addresses 301 Moved Permanently The requested page has moved to a new url 302 Found The requested page has moved temporarily to a new url 303 See Other The requested page can be found under a different url 304 Not Modified 305 Use Proxy 306 Unused This code was used in a previous version. It is no longer used, but the code is reserved 307 Temporary Redirect The requested page has moved temporarily to a new url  4xx: Client Error Message: Description: 400 Bad Request The server did not understand the request 401 Unauthorized The requested page needs a username and a password 402 Payment Required You can not use this code yet 403 Forbidden Access is forbidden to the requested page 404 Not Found The server can not find the requested page 405 Method Not Allowed The method specified in the request is not allowed 406 Not Acceptable The server can only generate a response that is not accepted by the client 407 Proxy Authentication Required You must authenticate with a proxy server before this request can be served 408 Request Timeout The request took longer than the server was prepared to wait 409 Conflict The request could not be completed because of a conflict 410 Gone The requested page is no longer available 411 Length Required The "Content-Length" is not defined. The server will not accept the request without it 412 Precondition Failed The precondition given in the request evaluated to false by the server 413 Request Entity Too Large The server will not accept the request, because the request entity is too large 414 Request-url Too Long The server will not accept the request, because the url is too long. Occurs when you convert a "post" request to a "get" request with a long query information 415 Unsupported Media Type The server will not accept the request, because the media type is not supported 416 417 Expectation Failed  HTTP… 26 5xx: Server Error Message: Description: 500 Internal Server Error The request was not completed. The server met an unexpected condition 501 Not Implemented The request was not completed. The server did not support the functionality required 502 Bad Gateway The request was not completed. The server received an invalid response from the upstream server 503 Service Unavailable The request was not completed. The server is temporarily overloading or down 504 Gateway Timeout The gateway has timed out 505 HTTP Version Not Supported The server does not support the "http protocol" version  URI, URL, and URN 27  URI stands for Uniform Resource Identifier, which is used to identify resource on the web.  A URI identifies a resource either by location, or a name, or both.  More often, most of us use URIs that defines a location to a resource.  URIs can be classified as Uniform Resource Locators (URLs), as Uniform Resource names (URNs), or as both.  A uniform resource name (URN) functions like a person's name, while a uniform resource locator (URL) resembles that person's street address.  In other words, the URN defines an item's identity, while the URL provides a method to find it.  URI, URL, and URN… 28 Fig Uniform Resource Identifier  URI, URL, and URN… 29  The World Wide Web can be conceived as a large group of resources placed in different computers all around the world.  These resources can be found and linked through URIs.  URI identifies resources by assigning them addresses in a given network.  A URL is a type of URI that's used to describe the location of a specific document.  A URL doesn't define the type of content to be found (texts, images, movies, etc.), it only shows where to find it.  URI, URL, and URN… 30  A common URL is composed by four parts:  The protocol: this specifies which protocol is used to access the document. It is also called URL scheme.  The computer name: gives the name of the computer, usually a domain name or IP address, where the content is hosted.  The directories path: Sequence of directories that define the path to follow to reach the document.  The file name: The name of the file containing the resource.  http://www.w3school.com/reference/tags/spain.html  For example, http://www.htmlquick.com/reference/tags/span.html Protocol: http:// Computer name (domain name): www.htmlquick.com Directories path: /reference/tags/ File name: span.html  URI, URL, and URN… 31  Other examples of URL are:  mailto:[email protected]  ftp://ftp.is.co.za/rfc/rfc1808.txt  tel:+1-816-555-1212  telnet://melvyl.ucop.edu/  file:///home/username/books/  A URN identifies a resource by name in a given namespace but not define how the resource maybe obtained.  URN functions like a person's name, while a URL resembles that person's street address.  In other words, the URN defines an item's identity, while the URL provides a method for finding it.  Domain Name Registration 32  A domain name is a unique name for a web site, like http://www.w3schools.com.  Domain names must be registered to be used for websites.  When domain names are registered, they are added to a large domain name register.  In addition, information about the web site, including the IP address, is stored on a DNS server.  Getting a domain name involves registering the name you want with an organization called ICANN (Internet Corporation for Assigned Names and Numbers) through a domain name registrar.  For example, if you choose a name like "example.com", you will have to go to a registrar, pay a registration fee and get registered.  That will give you the right to the name for a year, and you will have to renew it annually.  Domain Name Registration... 33  Domain registration information is maintained by the domain name registries, which contract with domain registrars to provide registration services to the public.  An end user selects a registrar to provide the registration service, and that registrar becomes the designated registrar for the domain chosen by the user.  Only the designated(select) registrar may modify or delete information about domain names in a central registry database.  Domain Name Registration... 34  A domain name registrar is an organization that manages the reservation of Internet domain names.  There are numerous domain name registrars.  Some of the popular ones are:  www.godaddy.com — This is a very popular registrar and possibly the biggest today offers.com domain names.  www.dotster.com — This fairly popular registrar provides fairly cheap domain prices.  www.register.com — This domain name registrar has been in business for a very long time.  Web Hosting 35  To make your Web site visible to the world, it has to be hosted on a Web server.  Hosting your web site on your own server is always an option.  Here are some points to consider:  Hardware Expenses  To run a real web site, you will have to buy some powerful server hardware.  Don't expect that a low cost PC will do the job.  You will also need a permanent (24 hours a day ) high-speed connection.  Software Expenses  Remember that server-licenses often are higher than client-licenses.  Also note that server-licenses might have limits on number of users.  Web Hosting... 36  Labor Expenses  Don't expect low labor expenses.  You have to install your own hardware and software.  You also have to deal with bugs and viruses, and keep your server constantly running in an environment where everything could happen.  To let others view your web pages, you must publish your web site.  To publish your work, you must copy your site to a web server.  Your own PC can act as a web server if it is connected to a network.  The most common approach is to use web hosting providers.  Web hosting means storing your web site on a public web server.  Web Hosting... 37  Some of the web hosting providers are: http://www.justhost.com/ http://www.ipage.com/ http://www.fatcow.com/ http://www.webhostinghub.com/  Things to Consider with selecting web hosting providers:  24-hour support  Make sure your ISP offers 24-hours support.  Don't put yourself in a situation where you cannot fix critical problems without having to wait until the next working day.  Toll-free phone could be vital if you don't want to pay for long distance calls.  Web Hosting... 38  Daily Backup  Make sure your ISP runs a daily backup routine, otherwise you may lose some valuable data.  Traffic Volume  Study the ISP's traffic volume restrictions.  Make sure that you don't have to pay a fortune for unexpected high traffic if your web site becomes popular.  Bandwidth or Content Restrictions  Study the ISP's bandwidth and content restrictions.  If you plan to publish pictures or broadcast video or sound, make sure that you can.  Web Hosting... 39  E-mail Capabilities  Make sure your ISP supports the e-mail capabilities you need.  Database Access  If you plan to use data from databases on your web site, make sure your ISP supports the database access you need. 40 End Of Chapter ?