Databases and Database Users

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Databases and Database Users

1. What is Database? Give an example.
A Database is a collection of related data. Here, the term ‘data’ means that known facts that can be recorded.
Ex. Any one suitable example (Telephone, Library, etc.)

2. Define – DBMS.
DBMS is a collection of programs that enables users to create and maintain a database.
<optional>
It is a general purpose software system that facilitates the process of defining, constructing and manipulating databases for various applications.

3. Mention various types of Databases.

Multimedia Database
Geographical Information System Database (GIS)
Data Warehouse or On-line Analytical Processing (OLAP) Database
Real-time or Active Database

4. What is meant by Concurrency?
A Database Management System must allow multiple users to access the database at the same time. To provide this facility, DBMS must include “Concurrency control” software to ensure that several users trying to update the same data at the same time.

5. Mention characteristics of Database Approach.

Self-describing Nature of a Database System
Insulation between Programs and Data, and Data Abstraction
Support of Multiple Views of the Data
Sharing of Data and Multi user Transaction Processing

6. Mention various levels of Database Actors.

Database Administrators
Database Designers
End-Users

Casual End User
Stand-alone Users
Sophisticated EU
Naïve/Parametric EU

System Analysts
Application Programmers

7. Mention the advantages of using DBMS.

Controlling Redundancy
Restricting unauthorized access
Providing persistent storage of Program Objects and Data Structures
Permitting inferencing and actions using rules
Providing multiple user interfaces
Representing Complex Relationships among data
Enforcing Integrity Constraints
Providing Backup and Recovery facilities

Chapter 2 – Database System Concepts and Architecture

8. Define Data Model.
A Data Model is a collection of concepts that can be used to describe the structure of a database.
It provides necessary means to achieve the abstraction (ie) hiding the details of data storage.

9. Mention the various categories of Data Model.

High Level or Conceptual Data Model
Low Level or Physical Data Model
Representational or Implementational Data Model
Relational Data Model
Network and Hierarchal Data Model
Record-based Data Model
Object-based Data Model

10. Define Schema.
The description of a database is called as “Database Schema” which is specified during database design and is not expected to change frequently until any changes needed.

11. Explain Schema Diagram with example.
The structure of a database (ie schema) is expressed in the form of diagrams. Such a diagram is called as “Schema Diagram”.
Ex. Any one example (Database with rows and its Schema Diagram)

12. What is “Snopshot” or “Database State”?
The data in the database at a particular moment is known as “Database State” of “Snapshot” of the Database.
<optional>
It is also called as current set of “Occurrences or Instances” in the database

13. What is Metadata?
The DBMS stores the descriptions of the schema constructs and constraints are called as “Meta Data”.
Or we simply called as data-about-data.

14. Mention the merits and demerits of Three-Schema Architecture.
Advantage:

Three Schema Architecture can make it easier to achieve true data independence, both physical and logical.

Disadvantages:

Two levels of mapping create and overhead during compilation
It leads inefficiency in the database management system.

15. Mention the various types of Database Languages.

Data Definition Language (DDL)
Storage Definition Language (SDL)
View Definition Language (VDL)
Data Manipulation Language (DML)

16. List out various components in DBMS.

Operating System
Data Manager
DDL Compiler
Run-time DB Processor
Query Compiler
Pre-compiler

17. Mention the various System Utilities of Database System.

Loading
Backup
File re-organization
Performance monitoring

18. Explain the classification of DBMS.

Object Relational DBMS (ORDBMS)
Distributed DBMS (DDBMS)
Homogenous DDBMS (HDDBMS)
Heterogeneous DBMS
On-line Transaction Processing (OLTP)

Chapter 3 – Data Modeling using ER Model

19. Define Entity with example.
Entity:
Entity is nothing but a thing in the real-world with an independent existence. An entity may be an object with a physical existence.
Ex. A person, a car, a house, etc.

20. Define : Entity Type, Entity Set and Value Set.
Entity Type:
An Entity Type defines a collection or set of entities that have the same attribute. Each Entity type in the database is described by its name and attributes.
Ex. Employee entity (draw its diagram)

Entity Set:
The collection of entities of a particular entity type are grouped into an ‘Entity Set”. It is also known as “Extension” of the Entity Type”.

Value Set:
Value set specifies the set of values that may be assigned to that attribute for each individual entity.
Ex. Age of employee ranges between 16 and 70.

21. Define : Relationship, Relationship Type, Roles.
Relationship:
In the Entity Relationship (ER) model, the references should not be represented as attributes, but as “Relationship”.
Ex. “Ken” is father of “John”. (draw its diagram)

Relationship Type:
A Relationship Type ‘R” among “n” entity types E1, E2, … En defines a set of associations or a “relationship set” among entities from these types.
Ex. Any suitable example with diagram.

Relationship Degree:
The degree of Relationship Type is the number of participating entity sets in it.
Ex. The WORKS_FOR relationship is of degree two.

A relationship type degree of two is known as “Binary Relationship Degree” and one of 3 degree is “Ternary Relationship Degree”.

22. What is Weak Entity Type?
Entity Types (ET) that do not have key attribute of their own are called as “Weak Entity Type”.
<optional>
In contrast, “Regular Entity Types” that do have a key attribute are sometimes called “Strong Entity Type”.

Chapter 4 – Enhanced ER and Object Modeling

23. What are the important concepts of EER Model?

Class and Sub-class Relationship
Type Inheritance
Specilisation and
Generelisation

24. Define “Category” or “Union Type”.
A subclass will represents a collection of objects that is (a subset of) the UNION of distinct Entity Type; we call such a sub-class as “Union Type” or “Category”.

Ex. VEHICLE_OWNER

25. What is Specific/Local Attributes?
Attributes that apply only to entities of a particular sub-class are called, “Specific or Local Attributes”.
Ex. ‘Pay Scale’ attribute in HOURLY_EMPLOYEE
This attribute only applicable for hourly employees, not for all.

26. Define Generalization.
The term Generalization refer to the process of defining a generalized entity type from the given Entity Type.

Uses:
1. Identify the common features (attributes)
2. Generalize them into a single “Super Class” of which the original entity types are special sub-classes.

27. Define Shared Sub Class or Multiple Inheritance.
A sub-class with more than one super classes is called as, “Shared Sub-class”.
Ex. ENGR_MGR must be

An Engineer
Salaried Employee
Manager

Which shares all the three super classes.
This concept is also known as “Multiple Inheritance”.

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