Database Reference
In-Depth Information
15. a. There is a many-to-many-to-many relationship between students, courses, and faculty
members.
b. There is a many-to-many relationship between students and courses. A faculty number func-
tionally determines a course number; that is, each faculty member is associated with exactly
one course.
c. There are separate many-to-many relationships between students and courses, courses and
faculty members, and students and faculty members.
d. There is a many-to-many relationship between students and courses. A given student
number-course number combination uniquely determines a faculty number. That is, when a
student takes a course, a single faculty member teaches the course.
e. There is a many-to-many relationship between students and courses. There is also a many-
to-many relationship between courses and faculty members. A student number functionally
determines a faculty number; that is, each student is associated with exactly one faculty
member.
17. If one 3NF relation contains a column that is a determinant for a column in another 3NF relation
with the same primary key, merging the relations will produce a relation that is not in third nor-
mal form. The following is an example of two such relations:
364
Student1 (StudentNum, LastName, FirstName, AdvisorNum)
Student2 (StudentNum, LastName, FirstName, AdvisorLast, AdvisorFirst)
The following is the result of merging the Student1 and Student2 relations:
Student (StudentNum, LastName, FirstName, AdvisorNum, AdvisorLast, AdvisorFirst)
This table is not in third normal form because:
AdvisorNum
!
AdvisorLast, AdvisorFirst
CHAPTER 7
DBMS FUNCTIONS
—
1. In updating and retrieving data, users do not need to know how data is physically structured on
disk nor what processes the DBMS uses to manipulate the data. These structures and manipula-
tions are solely the responsibility of the DBMS.
3. Most PC-based DBMSs contain a catalog that maintains metadata about tables, fields, table rela-
tionships, views, indexes, users, privileges, and replicated data. Large, expensive DBMSs usually
contain a data dictionary that serves as a super-catalog containing the same metadata as a catalog
and additional metadata such as that needed to track fragmented data.
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 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 correct 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.
Deadlock 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.
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