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Q5-4 How Do Database Applications Make Databases More Useful?

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Figure 5-16
Graphical Query: User Clicks on Security requirements are more stringent for browser-based Internet applications than
Video Icon to Find All Videos from for traditional ones. Most traditional applications run within a corporate network protected
That Location
from threats common on the Internet. Browser-based applications that are open to the public, over
the Internet, are far more vulnerable. Thus, protecting security is a major function for browser-
based Internet application programs. Like traditional database application programs, they need to
provide for data consistency and to handle special conditions as well. As an example of the need for
data consistency, consider the problems introduced by multi-user processing.

Multi-user Processing

Most traditional and browser-based applications involve multiple users processing the same
database. While such multi-user processing is common, it does pose unique problems that you,
as a future manager, should know about. To understand the nature of those problems, consider
the following scenario, which could occur on either a traditional or browser-based application.
At a ticket vendor’s Web site, two customers, Andrea and Jeffrey, are both attempting to buy
tickets to a popular event. Andrea uses her browser to access the site and finds that two tickets are
available. She places both of them in her shopping cart. She doesn’t know it, but when she opened
the order form, she invoked an application program on the vendor’s servers that read a database
to find that two tickets are available. Before she checks out, she takes a moment to verify with her
friend that they still want to go.
Meanwhile, Jeffrey uses his browser and also finds that two tickets are available because his
browser activates that same application that reads the database and finds (because Andrea has not
yet checked out) that two are available. He places both in his cart and checks out.
Meanwhile, Andrea and her friend decide to go, so she checks out. Clearly, we have a problem.
Both Andrea and Jeffrey have purchased the same two tickets. One of them is going to be disappointed.
This problem, known as the lost-update problem, exemplifies one of the special characteris-
tics of multi-user database processing. To prevent this problem, some type of locking must be used