On-line services, directories and other reference sources

On-line services, directories and other reference sources

On-line services are services that add values to the World Wide Web. Originally, these services built and maintained trunk networks that could be used by their customers. They also added their own content (such as extensive databases, news and weather reports, software libraries, etc.) to the Web. Users who are prepared to pay for the service can access this material. Customers still pay for some on the on-line services but the trend, in recent years, has been to make added value services free.

Web directories such, as Yahoo, offer an editorially selected, topically organised list of Web sites. To accomplish that goal, these sites employ editors to find new Web sites and work with programmers to categorize them and build their links into the site's searchable index. To make things even easier, all the major search engine sites now have built-in topical search indexes, and most Web directories had added keyword search facilities.

Web-based business directories provide access to companies within a wide range of sectors. Using a business directory makes it easily possible to locate companies in a particular sector and in a specific location (e.g. a chemical supplier in the West Midlands).

In addition, on-line reference sources, such as Wikipedia, provide an excellent source of information which can be freely accessed and even edited and updated by users. A typical reference source Web page is shown in Figure 2.12. A word of caution is necessary here: when searching for information on the Web it is advisable to consult several sources and then compare your results before placing reliance on the information that you find. The reason for this is that almost all can place information on the Web, but not all of them are accurate and some of them can be deliberately misleading!

Intranets

Intranets work like the Web (with browsers, Web servers and Web sites) but companies and other organizations use them internally. Companies use them because they let employees share corporate data, but they are cheaper and easier to manage than most private networks because nobody needs any software more complicated or more expensive than a web browser, for instance. They also have the added benefit of giving employees access to the web. Intranets are closed off from the rest of the Net by firewall software, which lets employees surf the Web but keeps all the data on internal Web servers hidden from those outside the company.

Test your knowledge 2.11

List TWO advantages and TWO disadvantages of a catalogue supplied on CD-ROM compared with one that is published on the World Wide Web.

Extranets

One of the most recent developments has been that of the extranet. Extranets are several intranets linked together so that businesses can share information with their customers and suppliers. Consider, for example, the production of a European aircraft by four major aerospace companies located in different European countries. They might connect their individual company intranets (or parts of their intranets) to each other, using private leased lines or even using the public Internet. The companies may also decide to set up a set of private newsgroups so that employees from different companies can exchange ideas and share information.

Test your knowledge 2.12

Briefly explain what is meant by a URL. Give an example of a URL for a UK-based engineering company. What is the URL of the Web page shown in Figure 2.9?

E-mail

Like ordinary mail, e-mail consists of a message, an address and a carrier that has the task of conveying the message from one place to another. The big difference is that e-mail messages (together with any attached files) are broken down into small chunks of data (called packets) that travel independently to their destination along with innumerable other packets travelling to different destinations. The packets that correspond to a particular e-mail message may travel by several different routes and may arrive out of order and at different times. Once all the packets have arrived, they are recombined into their original form. This may all sound rather complicated but it is nevertheless efficient because it prevents large messages hogging all of the available bandwidth. To put this into context, a simple page of A4 text can be transferred half-way round the world in less than a minute! Figure 2.13 shows a typical e-mail message written using Microsoft Outlook Express.