Database Reference
In-Depth Information
In addition, the existing data can be used in new ways, such as generating new types of reports,
without having to create additional data files, as is the case in the nondatabase approach.
3. Balancing conflicting requirements. For the database approach to function adequately within an
organization, a person or group should be in charge of the database, especially if the database will
serve many users. This person or group is often called the database administrator or database
administration (DBA), respectively. By keeping the overall needs of the organization in mind, a
DBA can structure the database in such a way that it benefits the entire organization, not just a
single group. Although this approach might mean that an individual user group is served less well
than it would have been if it had its own isolated system, the organization as a whole is better off.
Ultimately, when the organization benefits, so do the individual groups of users.
4. Controlling redundancy. With database processing, data that formerly was kept separate in
nondatabase, file-oriented systems is integrated into a single database, so multiple copies of the
same data no longer exist. With the nondatabase approach, each user group at Premiere Pro-
ducts has its own copy of each customer
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s address. With the database approach, each customer
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s
address would occur only once, thus eliminating redundancy.
Eliminating redundancy not only saves space but also makes the process of updating data
much simpler. With the database approach, changing a customer
s address means making one
change. With the nondatabase approach, in which data for each customer might be stored in
three different places, the same address change means that three changes have to be made.
Although eliminating redundancy is the ideal, it is not always possible. Sometimes, for rea-
sons having to do with performance, you might choose to introduce a limited amount of redun-
dancy into a database. However, even in these cases, you would be able to keep the redundancy
under tight control, thus obtaining the same advantages. This is why it is better to say that you
control redundancy rather than eliminate it.
5. Facilitating consistency. Suppose an individual customer
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s address appears in more than one
place. Customer 148, for example, might be listed at 2837 Greenway in one place and at 2856
Wisner in another place. In this case, the data for the customer is inconsistent. Because the
potential for this sort of problem is a direct result of redundancy and because the database
approach reduces redundancy, there is less potential for this sort of inconsistency occurring with
the database approach.
6. Improving integrity. An integrity constraint is a rule that data must follow in the database. For
example, the rep number given for any customer must be one that is already in the database. In
other words, users cannot enter an incorrect or nonexistent rep number for a customer. A data-
base has integrity when the data in it satisfies all established integrity constraints. A good DBMS
should provide an opportunity for users to incorporate these integrity constraints when they
design the database. The DBMS then should ensure that the constraints are not violated.
According to the integrity constraint about customers, the DBMS should not allow you to store
data about a given customer when the rep number you enter is not the number of a rep that
already is in the database.
7. Expanding security. Security is the prevention of unauthorized access to the database. A DBMS
has many features that help ensure the enforcement of security measures. For example, a DBA
can assign passwords to authorized users and then only those users who enter an acceptable pass-
word can gain access to the data in the database. Further, a DBMS lets you assign users to groups,
with some groups permitted to view and update data in the database and other groups permitted
only to view certain data in the database. With the nondatabase approach, you have limited secu-
rity features and are more vulnerable to intentional and accidental access and changes to data.
8. Increasing productivity. A DBMS frees the programmers who are writing database access pro-
grams from having to engage in mundane data manipulation activities, such as adding new data
and deleting existing data, thus making the programmers more productive. A good DBMS has many
features that allow users to gain access to data in a database without having to do any program-
ming. These features increase the productivity of programmers, who may not need to write com-
plex programs in order to perform certain tasks, and nonprogrammers, who may be able to get the
results they seek from the data in a database without waiting for a program to be written for them.
9. Providing data independence. The structure of a database often needs to be changed. For
example, changing user requirements might necessitate the addition of an entity, an attribute,
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