AS Web Applications

The internet is the global communications system which links all computer together. The links can be made thorugh various communication measure such as telephone lines and satellites. it allows for fast communication between devices. Messages and data are passed from the source computer through other computers until it reaches the destination device.

The WWW is a collection of information that has grown up on a computer connected to the internet. This information is held in multimedia form and is stored in locations called websites in the form of web pages.

A URL is a unique adress for referring to resouces on the internet. If the protocol is omitted, http:// is assumed, as this is the most common protocol. If a filename is omitted, index.htm is normally assumed. Even when the filename is given htm (or html) will if no extension is present.

HTTP is a protocol that defines the process of identifying, requesting and transferring multimedia web pages over the internet. These webpages are usually constructed using html, and a secure variant HTTPS exists.

Each computer linked to the internet has a physical address, a number called an IP address. The IP address uniquely identifies the physical computer linked to the internet. The domain name server converts the domain name into its corresponding IP address, which is in the form of:

158.152.1.58

Some computers are connected to the internet at all times, these have static IP addresses while computers which are provided internet access through an ISP are assigned a dynamic IP address when logging on.

A web browser is the application on a users computer that is responsible for requesting the text and graphics of webpages from severs on the internet, and assembling them for display.

Most browsers allow to user to store the page address of sites they frequently visit as a bookmark or favourite.

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

A web hosting service is a type of internet hosting service that allows individuals and organisations 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.

FTP is the most commom 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. When a user downloads files through FTP they are given freer acess 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 usernames and passwords are often required.

An ISP is an organisation that has direct links to the internet an accepts transmissions from users over dial-up or broadband connections, and passes these onto the internet. Most people acess the internet through any one of a number of commercial internet service providers such as BT.

A search engine is an application accessed over the internet that maintains the indexes of webpages. Users wanting information on a particular topic will access the search engine using the internet and submit a topic or list of topics. The seach engine will then 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.

A cache is a store of recently accessed webpages and the images they contain, kept by a browser. Because transmitting than is necessary over the internet is inefficient, if a user revisits a page that is already stored in a cache, it can be loaded form the local copy, without needing to access the internet. Further, as commercial websites frequently repeat the same information such as a company logo on different pages, it is not necessary to download all of this data again. This process is not without pitfalls. The user may be accessing the web page regularly 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 periodically, or for the user to force a webpage to reload over the internet even when it is already in the cache.

Cookies are small files placed on the hard drive of a users 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 to 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. This is because of suspicions they have about what information is being gathered about them.

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 commercial advantages for a portal in attracting as many users as possible, becuase they can sell adverting on the site. To be useful to the indivudual, the site must offer services that the user need 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.

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

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 users 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.