Database Reference
In-Depth Information
or a relationship, or a change might be required to improve performance. A good DBMS provides
data independence, which is a property that lets you change the structure of a database without
requiring you to change the programs that access the database; examples of these programs are
the forms you use to interact with the database and the reports that provide information from
the database. Without data independence, programmers might need to expend a great deal of
effort to update programs to match the new database structure. The presence of many programs
in the system may make this effort so prohibitive that management might decide to avoid
changing the database, even though the change might improve the database
14
s performance or
add valuable data. With data independence, management is more likely to make the decision to
change the database.
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DISADVANTAGES OF DATABASE PROCESSING
As you would expect, when there are advantages to doing something in a certain way, there are also disad-
vantages. Database processing is no exception. In terms of numbers alone, the advantages outweigh the dis-
advantages; the latter are listed in Figure 1-14 and explained next.
1.
Larger file size
2.
3.
4.
Increased complexity
Greater impact of failure
More difficult recovery
FIGURE 1-14
Disadvantages of database processing
1. Larger file size. To support all the complex functions that it provides to users, a DBMS must be
a large program that occupies a great deal of disk space, as well as a substantial amount of inter-
nal memory. In addition, because all the data that the database manages for you is stored in one
file, the database file requires a large amount of disk space and internal memory.
2. Increased complexity. The complexity and breadth of the functions provided by a DBMS make
it a complex product. Users of the DBMS must learn a great deal to understand the features of
the system in order to take full advantage of it. In the design and implementation of a new sys-
tem that uses a DBMS, many choices have to be made; it is possible to make incorrect choices,
especially with an insufficient understanding of the system. Unfortunately, a few incorrect
choices can spell disaster for the whole project. A sound database design is critical to the suc-
cessful use of a DBMS.
3. Greater impact of failure. In a nondatabase, file-oriented system, each user has a completely
separate system; the failure of any single user
s system does not necessarily affect any other
user. On the other hand, if several users are sharing the same database, a failure on the part of
any one user that damages the database in some way might affect all the other users.
4. More difficult recovery. Because a database inherently is more complex than a simple file, the
process of recovering it in the event of a catastrophe also is more complicated. This is particu-
larly true when the database is being updated by many users at the same time. The database
must first be restored to the condition it was in when it was last known to be correct; any
updates made by users since that time must be redone. The greater the number of users
involved in updating the database, the more complicated this task becomes.
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INTRODUCTION TO THE HENRY BOOKS DATABASE CASE
Henry Books is a bookstore chain owned by Ray Henry, who sells used topics and remainders in his stores.
To support his growing mail order and Internet business, he stores his data in a database to ensure that his
data is current, accurate, and easily accessible.
