PLUS TWO COMPUTER APPLICATION
(+2 Computer Application / Computer Science ,
Previous Questions Chapter wise ..
Chapter 8. Database Management System
1...................... level describes only a part of a database
(a) View
(b) Physical
(c) Logical
(d) None of these
2. What is relational algebra ?Explain any three relational algebra operations
Once the database is designed and data is stored, the required
information is to be retrieved. A variety of operations are provided by RDBMS.
The collection of operations that is used to manipulate the entire relations of a
database is known as relational algebra.
1.Selection operation
SELECT operation is used to select rows from a relation that satisfies a given
predicate. The predicate is a user defined condition to select rows of user's choice.
This operation is denoted using lower case letter sigma (σ ). The general format of
select is as follows:
σ condition (Relation)
The result of SELECT operation is another relation containing all the rows satisfying
the given predicate (or conditions).
2.Project operation
The PROJECT operation selects certain attributes from the table and forms a new
relation. If the user is interested in selecting the values of a few attributes, rather
than all the attributes of the relation, then use PROJECT operation. It is denoted by
lower case letter π . The general format of project operation is as follows:
π A1, A2,…., An (Relation)
Here A1, A2, . . . ., An refer to the various attributes that would make up the
relation specified.
3.Union operation
UNION operation is a binary operation and it returns a relation containing all tuples
appearing in either or both of the two specified relations. It is denoted by ∪ . The
two relations must be union-compatible, and the schema of the result is defined to
be identical to the schema of the first relation. If two relations are union-compatible,
then they have the same number of attributes, and corresponding attributes, taken
in order from left to right, have the same domain. Note that attribute names are not
used in defining union-compatibility.
3. The number of attributes in a relation is called …………
(a) tuple
(b) degree
(c) cardinality
(d) domain
Ans. b
4. Explain the components of DBMS
DBMS have several components, each performing very significant tasks in its
environment. The components are
• Hardware
• Software
• Data
• Users
• Procedures
Hardware: The hardware is the actual computer system used for storage and
retrieval of the database. This includes computers (PCs, workstations, servers and
supercomputers), storage devices (hard disks, magnetic tapes), network devices
(hubs, switches, routers) and other supporting devices for keeping and retrieval of
data.
Software: The software
part consists of the actual
DBMS, application
programs and utilities.
DBMS acts as a bridge
between the user and the
database. In other words,
DBMS is the software that
interacts with the users,
application programs, and
databases. All requests from
users for access to the
database are handled by the DBMS
Data: It is the most important component of DBMS environment from the end users point of view. The database contains operational data and the meta-data (data about data). The database should contain all the data needed by the organization. The major feature of databases is that the actual data and the programs that uses the data are separated from each other. For effective storage and retrieval of information, data is organized as fields, records and files.
Fields: A field is the smallest unit of stored data. Each field consists of data of a specific type
Record: A record is a collection of related fields.
File: A file is a collection of all occurrences of same type of records.
Users: There are a number of users who can access data on demand using application programs. The users of a database system can be classified depending on the mode of their interactions with DBMS. The different categories of users are Database Administrator (DBA), Application Programmers, Sophisticated users and Naive Users.
Procedures: Procedures refer to .the instructions and rules that govern the design and use of the database. The users of the system and the person that manages the database require documented procedures on how to use or run the system.
5. A candidate key that is not a primary key is called -----------------
Ans. Alternate key
6. Define the term
a. Degree
b. Cardinality
Ans. The number of attributes in a relation determines the degree of a relation.
The number of rows or tuples in a relation is called cardinality of the relation.
6. Define data abstraction and explain any two levels of abstraction
For the system to be usable, it must retrieve data efficiently. The need for efficiency has led designers to use complex data structures to represent data in the database. Since many database system users are not computer trained, developers hide the complexity from users through several levels of abstraction. The data in a DBMS is described at three levels of abstraction.
a. Physical level
b. Logical level
7. Define the terms
1. Fields
2. Record.
Ans. Fields: A field is the smallest unit of stored data. Each field consists of data of a specific type
Record: A record is a collection of related fields.
8. In RDBMS contain 10 rows and 5 columns.what is the degree of the relation ?
Ans. 5
9.Is it possible SELECT and PROJECT operations of relational algebra in single statement?Explain with example?
Not possible SELECT and PROJECT operations of relational algebra in single statement.
Select Operation : This operation is used to select rows from a table (relation) that specifies a given logic, which is called as a predicate. The predicate is a user defined condition to select rows of user's choice.
Project Operation : If the user is interested in selecting the values of a few attributes, rather than selection all attributes of the Table (Relation), then one should go for PROJECT Operation.
Data: It is the most important component of DBMS environment from the end users point of view. The database contains operational data and the meta-data (data about data). The database should contain all the data needed by the organization. The major feature of databases is that the actual data and the programs that uses the data are separated from each other. For effective storage and retrieval of information, data is organized as fields, records and files.
Fields: A field is the smallest unit of stored data. Each field consists of data of a specific type
Record: A record is a collection of related fields.
File: A file is a collection of all occurrences of same type of records.
Users: There are a number of users who can access data on demand using application programs. The users of a database system can be classified depending on the mode of their interactions with DBMS. The different categories of users are Database Administrator (DBA), Application Programmers, Sophisticated users and Naive Users.
Procedures: Procedures refer to .the instructions and rules that govern the design and use of the database. The users of the system and the person that manages the database require documented procedures on how to use or run the system.
5. A candidate key that is not a primary key is called -----------------
Ans. Alternate key
6. Define the term
a. Degree
b. Cardinality
Ans. The number of attributes in a relation determines the degree of a relation.
The number of rows or tuples in a relation is called cardinality of the relation.
6. Define data abstraction and explain any two levels of abstraction
For the system to be usable, it must retrieve data efficiently. The need for efficiency has led designers to use complex data structures to represent data in the database. Since many database system users are not computer trained, developers hide the complexity from users through several levels of abstraction. The data in a DBMS is described at three levels of abstraction.
a. Physical level
The lowest level of abstraction describes how data is actually stored on secondary storage devices such as disks and tapes. The physical level describes complex lowlevel data structures in detail. We must decide what file organisations are to be used to store the relations and create auxiliary data structures, called indexes, to speed up data retrieval operations.
b. Logical level
The next-higher level of abstraction describes what data is stored in the database, and what relationships exist among those data. The logical level thus describes the entire database in terms of a small number of relatively simple structures.Although mplementation of the simple structures at the logical level may involve complex physical-level structures, the user of the logical level does not need to be aware of this complexity. Database administrators, who must decide what information to keep in the database, use the logical level of abstraction. Logical level is also referred as conceptual level.
7. Define the terms
1. Fields
2. Record.
Ans. Fields: A field is the smallest unit of stored data. Each field consists of data of a specific type
Record: A record is a collection of related fields.
8. In RDBMS contain 10 rows and 5 columns.what is the degree of the relation ?
Ans. 5
9.Is it possible SELECT and PROJECT operations of relational algebra in single statement?Explain with example?
Not possible SELECT and PROJECT operations of relational algebra in single statement.
Select Operation : This operation is used to select rows from a table (relation) that specifies a given logic, which is called as a predicate. The predicate is a user defined condition to select rows of user's choice.
Project Operation : If the user is interested in selecting the values of a few attributes, rather than selection all attributes of the Table (Relation), then one should go for PROJECT Operation.
Example in SELECT operation
σ sales > 50000 (Customers)
Output - Selects tuples from Customers where sales is greater than 50000
Example in PROJECT operation
| CustomerID | CustomerName | Status |
| 1 | Active | |
| 2 | Amazon | Active |
| 3 | Apple | Inactive |
| 4 | Alibaba | Active |
Here, the projection of CustomerName and status will give
Π CustomerName, Status (Customers)
| CustomerName | Status |
| Active | |
| Amazon | Active |
| Apple | Inactive |
| Alibaba | Active |
