DATABASES AND THE INTERNET - Fundamentals of Database Management Systems - page 376

site on a worldwide basis, which, after all, is one of the hallmarks of e-commerce.
Three o'clock in the morning in one part of the world is the middle of the day in
another, and so the system really has to be up all of the time. There are several
reasons that an information system can be unavailable.

Because of some kind of system or telecommunications failure.

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Because of the failure of a support system, such as an electrical outage.

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Because of a planned down period for system maintenance.

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Because of excessive traffic that clogs the system. ■

Here again, the challenge is to make the information systems and their
databases available 24/7 without going overboard in terms of cost. Regarding system
failure, electrical outages, and planned maintenance time, redundant computer
hardware and such accessories as electrical generators and batteries will do the job.
The trick is to accomplish this at a reasonable cost. Excessive traffic is another story.
Legitimate traffic spikes, as discussed above, can certainly reduce availability.
But computer viruses that reproduce many copies of themselves and automated
''robots'' searching Web sites for information can clog systems, too. Either these
must be prevented or the system must be constantly monitored by software that
watches for such conditions.
One technique used to improve availability is known as clustering .Acluster
of several servers is built, each with its own replicated copy of the database. As
queries come in over the Web, sophisticated software checks the activity on each
of the servers and their databases and performs '' load balancing ,'' sending each
particular query to a server that is relatively idle at that moment.

Scalability
Some electronic commerce efforts, in both ''pure'' e-commerce start-up companies
and established companies, have experienced rapid growth. In one case, the growth
rate in traffic to a Web site was estimated at 1000-4000 % per year in the early years.
This is certainly good news for the company that experiences it! But the information
system that supports this Web site and its traffic growth must be scalable; that is, it
must be capable of growing without adversely affecting the operations of the site. It
is thus imperative to choose that hardware and software that is capable of rapid and
major expansion.

Security and Privacy
In Chapter 11 we discussed data security at some length. Now, consider the Internet
database environment in which all of the traditional data security concerns are
still present but in addition, the information system is exposed to the whole world
through its Web site! And that is not an exaggeration. In the business-to-consumer
e-commerce environment, the company wants as many people as possible to visit its
Web site and buy its products. But that also means that hackers, data thieves, virus
writers, and anyone else with mischief on their minds has an openly published entry
point into the company's information system. Obviously, this requires heavy-duty
security, such as:

Separating the different parts of the information system so that they run on
different computers. Thus, the Web server and the database server should be

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