Databases Reference
In-Depth Information
5. A lost update could occur in a concurrent update situation when two users attempt to update the
same data at the same time, and the DBMS does not does not have concurrency update features
such as two-phase locking or timestamping.
7. A transaction is a set of steps completed by a DBMS that accomplishes a single user task; the DBMS
must successfully complete all transaction steps or none at all for the database to remain in a cor-
rect state.
9. Deadlock occurs in a concurrent update situation when the first user is waiting for data that has
been locked by a second user, and the second user is waiting for data that has been locked by the
first user. Unless outside action occurs, each user could wait for the other's data forever. Dead-
lock occurs when each of the two users is attempting to access data that is locked by the other user.
11. Recovery is the process of returning the database to a state that is known to be correct from a state
known to be incorrect.
13. A DBA uses forward recovery when a catastrophe destroys a database. Forward recovery consists of
two steps. First, the DBA copies the most recent database backup over the live database. Second, the
DBMS forward recovery feature uses the log to apply after images for committed transactions.
15. Security is the prevention of unauthorized access, either intentional or accidental, to a database.
17. Authentication refers to techniques for identifying the person who is attempting to access the DBMS.
Three types of authentication are passwords, biometrics, and database passwords. A password is a
string of characters assigned by the DBA to a user that the user must enter to access to the database.
Biometrics identify users by physical characteristics such as fingerprints, voiceprints, handwritten
signatures, and facial characteristics. A database password is a string of characters assigned by the DBA
to a database that users must enter before they can access the database.
19. Permissions specify what kind of access a user has to objects in a database. A workgroup is a group
of users, and a DBA usually assigns appropriate permissions to workgroups.
21. Privacy refers to the right of individuals to have certain information about them kept confidential.
Privacy and security are related because it is only through appropriate security measures that pri-
vacy can be ensured.
23. Data independence is a property that lets you change a database structure without requiring you
to change the programs that access the database.
25. Some utility services that a DBMS should provide include: services that let you change the data-
base structure; services that let you add new indexes and delete indexes that are no longer needed;
facilities that let you use the services available from your operating system; services that let you
export data to and import data from other software products; services that provide support for
easy-to-use edit and query capabilities, screen generators, report generators, and so on; support
for both procedural and nonprocedural languages; and support for an easy-to-use menu-driven or
switchboard-driven interface that allows users to tap into the power of the DBMS without having
to resort to a complicated set of commands.
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1. The DBA is the database administrator, or the person responsible for the database. The DBA is nec-
essary because his responsibilities are critical to success in a database environment, especially
when the database is shared among many users.
3. After the DBA determines the access privileges for each user, the DBA creates security policies
and procedures, obtains management approval of the policies and procedures, and then distrib-
utes them to authorized users. The DBA uses the DBMS's security features, such as encryption,
authentication, authorizations, and views, and uses special security programs, if necessary.
Finally, the DBA monitors database usage to detect potential security violations and takes correc-
tive action if a violation occurs.
5. Certain data, although no longer needed in the production database, must be kept for future reference.
A data archive is a place for storing this type of data. The use of data archives lets an organization keep
data indefinitely, without causing the database to become unnecessarily large. Data can be removed
from the database and placed in the data archive, instead of just being deleted.
7. A shared lock permits other users to read the data. An exclusive lock prevents other users from
accessing the data in any way.
