Anintangible entityis an entity that does not have a physical presence but still holds meaning in a database. These entities representconcepts, relationships, or abstract datathat exist in a logical sense.
Example Usage in Databases:
Customer Loyalty Status (Gold, Silver, Bronze)
Theloyalty levelis anintangible entitysince it is derived from other data (purchase history).
Online User Sessions
Asession IDexistslogically in the systembut does not have a tangible presence like a product or employee.
Why Other Options Are Incorrect:
Option A (Concrete entity) (Incorrect):No such formal term in database design.
Option B (Tangible entity) (Incorrect):Represents somethingphysical, like anemployeeorproduct.
Option D (Physical entity) (Incorrect):Refers todata stored on disk, like database tables or indexes.
Thus, the correct answer isIntangible entity, as it only exists in a logical sense within the database.
What is the role of a query processor in the database system architecture?
Options:
A.
It uses information from the catalog to perform query optimization.
B.
It writes log records before applying changes to the database.
C.
It translates instructions into file system commands.
D.
It sends results back to the application that requested the queries.
Answer:
A
Explanation:
Aquery processoris responsible forquery optimization and executionin a database management system (DBMS). It analyzes SQL statements, optimizes execution plans, and ensures efficient retrieval of data.
Option A (Correct):Thequery processoroptimizes queries by analyzing metadata from thesystem catalogto determine the best execution strategy.
Option B (Incorrect):Logging transactionsbefore applying changes is the responsibility of thetransaction manager.
Option C (Incorrect):Translating instructions intofile system commandsis handled by thestorage manager, not the query processor.
Option D (Incorrect):While the query processor helps retrieve results, thedatabaseengineandAPI layerare responsible for returning results to applications.
[Reference:Query optimization and execution in relational databases., ]
Question 3
How can a primary key constraint be added after the table is created?
Options:
A.
By using an ALTER clause
B.
By using the CREATE TABLE statement
C.
By using an UPDATE clause
D.
By using an INSERT INTO clause
Answer:
A
Explanation:
Toadd a primary key constraint after table creation, we use theALTER TABLEstatement.
Example Usage:
sql
ALTER TABLE Employees
ADD CONSTRAINT PK_Employees PRIMARY KEY (EmpID);
Thisaddsa primary key to the EmpID columnafter the table was created.
Why Other Options Are Incorrect:
Option B (CREATE TABLE) (Incorrect):Used for defining constraintsduringtable creation, not after.
Option C (UPDATE) (Incorrect):Modifiesrow values, not constraints.
Option D (INSERT INTO) (Incorrect):Used toadd datato a table, not modify constraints.
Thus, the correct answer isALTER TABLE, as itmodifies table structure to add a primary key constraint.