AS web applications

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Internet

Internet: The internet is a global communications system linking computers in geoghraphically separte

variety of telecommunications: telephone lines, satellite

It allows for fast communications between:computers, mobile phones, PDA's, transfer of data between computers, distribution of information

Messages and data are passed fom the source computer, through other computers, until the destination computer is reached.

Any computers can be linked to any other computer attached to the internet; this can be achieved by:having common technical standards, a common identification system for computers, a common refernce system for data files

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World Wide Web

World Wide Web 

The world wide web is a collection of information that has grown up on computer connected to the internet.

The information is held in multimedia form and is stored in locations called websites in the form of web pages.

The process of searching the web for information and following links to other information is known as surfing

Uniform Resource Locator

A URL is a unique address for referring to resources on the internet. although most internet resources are accessed by clicking on the hyperlinks and it is rarely necessary to type URL in full, most browsers have defaults for portions of the URL. If the protocol is omitted, http:// is assumed, at this is the commonest protocol. If a filename is omtted index.htm is normally assumed. Even when the filename is given htm will be assumed if no extension present

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Hypertext Transfer Protocol (HTTP)

Hypertext Transfer Protocol (HTTP)

Http is a protocol that defines the proccess of identifying, requesting and transferring multipedia web pages over the internet. These web pages are usually constructed using HTML and a secure variant HTTPS exists.

IP Address

Each computer linked to the internet has a physical address, a number called an IP Address. The IP Adresses(Internet Protocol) address uniquely identifies the physical computer linked to the internet. The domain name server convertsthe domain name into its corresponding IP address, which is in the form of: 158.152.1.58

Some computers are potentially connected to the internet at all times- these always have the same IP address, a so called static IP address. Other, which access the internet through an ISP, are assigned a dynamic IP address when logging in, one of the range allocated to that ISP: this address might be different on subsequent log-ins 

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Web Browser

Web Browser

A web browser is the application running on a user's computer that is responsible for requesting the text and graphics of webpages from servers on the internet, and assembling them for display. The commonest browsers are Microsoft Internet Explorer, Mozilla Firefox, Apple Safari, Google Chrome and Opera. 

Most browsers allow the user to save the page address of sites they intend to visit often, as a bookmark or favourite. These sites can then be accessed by selecting from the list of bookmarks rather than typing in full URL.

Although all browsers attempt the same task-displaying a webpage as the designer intended- there are many differences between them, some trivial, some significant not all browsers implement the full set of features defined by the World Web Consortiun 

MICROSOFT INTERNET EXPLOERER-FIREFOX-SAFARI-OPERA-GOOGLE CHROME

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Web server

Web Server 

A web server provides internet pages for other computers through the internet. It often provides the cache of web pages, which are pages stored when first accessed so they can be supplied later without the delay of accessing the internet. 

Web Hosting

web hosting service is a type of internet hosting service that allows individuals and organizations to make their website accessible via the World Wide Web. Web hosts are companies that provide space on a server owned or leased for use by clients, as well as providing internet connectivity to the internet for other servers located in their data center

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FTP (File Transfer Protocol)

FTP is the commonest protocol for the movement of files across the internet. Users can access a server holding the required file and request that it be downloaded to them;alternatively a user can send a file to a server that will accept uploads- it is in this way that most personal web pages are delivered to the web server where they are stored.when a user downloads files through FTP they are given freer access to the file server than to a web server. They can normally see a listing of all files and folders, and may be able to navigate through the directory structure. For this reason, passwords and usernames are frequently required, and vertifying these is an added task for the server. 

ISP(Internet Service Provider) Is an organization thats has direct links to the internet and accepts transmissions from users over dial-up or broadband connections, and passes these onto the internet. Most individual users of the internet access through any one of a number of commercial internet service providers. E.g. Sky, BT, EE etc

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Search Engine

Search Engine: A search engine is an application accessed over the internet that maintains the indexes of webpages. Users wanting information on a particular topicwill access the search engine using the internet and submit a topic or list of topics. The search engine will compare this list with the pages in its index and generate a page of hyperlinks that the user can click, to go to the most relevant webpages.---As most search engines index many millions of pages, there is great importance for commericial websites in being among the first few hyperlinks reported. In creating these reports, search engines attempt to rank pages in terms of usefulness, by noting how often the words searched for appear on the pages, or how often other pages link to that page.

Cache: A cache is a store of recently accessed webpages and the images they contain, kept by a browser. Because transmitting more information than is strictly necessary over the internet is inefficient, if a user revisits a page that is already stored in the cache, it can be loaded from the local copy, without needing to access the internet. Further, as commercial websites frequently repeat the same information on different pages, it is not necessary to download all of this data again.This process is not without pitfalls. The user may be accesing the web page regulary to see if there is anything new. If the page is reloaded from the cache, it will appear identical to the page on the last visit.Browsers allow cached files to be deleted, or force reloads of a page

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Cookies

Cookies: Cookies are small files placed on the hard drive of a user's computer by a website that he or she has visited. On a subsequent visit to the same site, the cookie detected and the site knows that the user has visited before.Personal information that they have already entered need not be requested again, and the owner of the site can build up a picture of what the user sees on repeated visits. Users are free to block cookies and may routinely do so. This is generally because of suspicions they have about what information is being gathered about them.

Portal: A portal is a website designed to be the one that a user will want to visit first when accessing the web. There are obvious commericial advantages for a portal in attracting as many users as possible, because they can sell advertising on the site. To be useful to the individual, the site must offer services that the user needs regularly, such as search facilities, news updates and so on.

In most cases, a portal site allows the user to create their own customized page, made up of links to information that the user chooses. For example the latest news headlines might be displayed: these will be loaded from a news site, but will appear in the portal

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Website

Website: A website is a collection of webpages at the same domain, often with a common theme and usually maintained by a single individual or organization. The user moves between pages by clicking on hyperlinks. This causes a new page to be loaded, or parts of the existing page to be refreshed with new information.

Webpages: A webpage is a 'document' accessed in a browser. It will generally contain text and graphics and may well contain audio or video. Aside from text these elements are not stored on the webpage itself, but are loaded into the page by the user's browser from the location specified by a URI (Uniform Resource Identifier) contained in the page. For large files, such as video and audio material, streaming may be used.

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