DATA Base system

Question 1

description of the entire database structure that is used by the database software to maintain the database

Answer 1

schema

Question 2

description of only that portion of the database pertinent to a particular user’s needs.

Answer 2

subschema

Question 3

the application software does not directly manipulate the data- base. The actual manipulation of the database is accomplished by the

Answer 3

database management system (DBMS)

Once the application software has determined what action the user is requesting, it uses the DBMS as an abstract tool to obtain the results. If the request is to add or delete data, it is the DBMS that actually alters the database. If the request is to retrieve information, it is the DBMS that performs the required searches

Question 4

the application software does not have to be concerned with whether the database is stored on a single machine or scattered among many machines within a network

Answer 4

distributed database

Question 5

the ability to change the database itself without changing the application software.

Answer 5

data independence

Question 6

a DBMS contains routines that translate commands stated in terms of a conceptual view of the database into the actions required by the actual data storage system. This conceptual view of the database is called a

Answer 6

database model.

Question 7

A row in a relation is called

Answer 7

tuple

Question 8

Columns in a relation are referred

Answer 8

attributes

Question 9

relation no longer contains one tuple for each employee but rather one tuple for each assignment of an employee to a job, how can this resolve?

Answer 9

we can solve our problems by redesigning the system using three relations—one for each of the preceding categories. We can keep the original relation in Figure 110 (which we now call the EMPLOYEE relation) and insert the additional information in the form of the two new relations called JOB and ASSIGNMENT, which produces the database

Question 10

Select Operation

Answer 10

Select from employee where emplID=123

Question 11

project Operation

Answer 11

Project name, address from employee

Question 12

Join Operation

Answer 12

Join A and B where A.W=B.X

Question 13

The links between objects in an object-oriented database are normally maintained by the

Answer 13

DBMS
so the details of how these links are implemented are not a concern of the programmer writing application software. Instead, when a new object is added to the database, the application software merely specifies the other objects to which it should be linked. The DBMS then creates any linkage system that might be required to record these associations. In particular, a DBMS might link the objects representing the assignments of a given employee in a manner similar to a linked list.

Question 14

Another task of an object-oriented DBMS is to provide ——————— for the objects entrusted to it—

Answer 14

permanent storage

Question 15

objects that are created and added to a database must be saved after the program that created them terminates. Such objects are said to be———-

Answer 15

persistent objects (which assigned storage)

Question 16

Advantage of Object oriented database over relational data base?

Answer 16

If an entire name is stored as a single attribute in a relation, then inquiries regarding only surnames are awkward. However, if the name is stored as individual attributes, such as first name, middle name, and surname, then the number of attributes becomes problematic because not all names con- form to a specific structure—even when the population is restricted to a single culture. In an object-oriented database, these issues can be hidden within the object that holds the employee’s name. An employee’s name can be stored as an intelligent object that is capable of reporting the related employee’s name in a variety of formats. Thus, from outside these objects, it would be just as easy to deal with only surnames as with entire names, maiden names, or nicknames.

Question 17

guarding against problems such as operations that for some reason are only partially completed or different operations that might interact inadvertently to cause inaccurate information in the database.

Answer 17

Maintaining DB Integrity

Question 18

The point at which all the steps in a transaction have been recorded in the log is called

Answer 18

commit point.

Question 19

If problems should arise before a transaction has reached its commit point, the DBMS might find itself with a partially executed transaction that cannot be completed. In this case the log can be used to

Answer 19

roll back

Question 20

If one transaction reads the account’s current balance at the point when the other has just read the balance but has not yet calculated the new balance, then both transactions will base their deductions on the same initial balance. In turn, the effect of one of the deductions will not be reflected in the database.

Answer 20

locking protocol
In a locking protocol, each time a transaction requests access to a data item, it must also tell the DBMS the type of access it requires. If a transaction requests shared access to an item that is either unlocked or locked with a shared lock, that access is granted, and the item is marked with a shared lock. If, however, the requested item is already marked with an exclusive lock, the additional access is denied. If a transaction requests exclusive access to an item, that request is granted only if the item has no lock associated with it. In this manner, a transaction that is going to alter data protects that data from other transactions by obtaining exclusive access, whereas several transactions can share access to an item if none of them are going to change it. Of course, once a transaction is finished with an item, it notifies the DBMS, and the associated lock is removed.

Question 21

sequential file

Answer 21

file that is accessed in a serial manner from its beginning to its end as though the information in the file were arranged in one long row. Examples include audio files, video files, files containing programs, and files containing textual documents

Question 22

Indexed Files

Answer 22

An index for a file contains a list of the keys stored in the file along with entries indicating where the record containing each key is stored. Thus to find a particular record, one finds the identifying key in the index and then retrieves the block of information stored at the location associated with that key.

Question 23

a record to be located by means of a key value. But, rather than looking up the key in an index, ————- identifies the location of the record directly from the key.

Answer 23

Hashing

Question 24

techniques for discovering patterns in collections of data.

Answer 24

Data mining

Question 25

Social Impact of Database Technology

Answer 25

the purchasing patterns of credit card holders can be classified and cross-listed to obtain customer profiles of immense marketing value. Subscription forms for body-building magazines can be mailed to those who have recently purchased exercise equipment, whereas subscription forms for dog obedience magazines can be targeted toward those who have recently purchased dog food. Alternative ways of combining information are sometimes very imaginative. Welfare records have been compared to criminal records to find and apprehend parole violators, and in 1984 the Selective Service in the United States used old birthday registration lists from a popular ice cream retailer to identify citizens who had failed to register for the military draft.