CH 1: Introduction

Question 1

Physical Data Independence

Answer 1

Implementation of

simple data structures at the Logical Level

may depend on

complex structures at the Physical Level

But a user at the Logical Level doesn’t have to be aware of the complex physical structures

Question 2

Definition:

“Instance” of a Database

Answer 2

The collection of information stored in a database at a particular moment

Question 3

Levels of

Data Abstraction

Answer 3

View Level

Logical Level

Physical Level

Question 4

Levels of Data Abstraction:

View Level

Answer 4

View Level

• The highest level
• Describes only part of the database
• Exists to simplify user interaction with the system
• There may be many views for the same database

Question 5

Levels of Data Abstraction:

Logical Level

Answer 5

Logical Level

• Describes :
  
  • What data are stored
  • What relationships exist between data
• Describes the entire database in terms of simple structures

Question 6

Levels of Data Abstraction:

Physical Level

Answer 6

Physical Level

• Lowest Level
• Describes how data is actually stored
• Describes low-level data structures in detail.

Question 7

DBMS

Overview

Answer 7

Database Management System

• A collection of interrelated data, and
• A set of programs to access the data
• The Primary Goal of a DBMS is to provide a way to store and retrieve database information that is both convenient and efficient

Question 8

Definition:

Query

Answer 8

Query

A statement requesting the retrieval of information

Question 9

Definition:

Query Language

Answer 9

Query Language

The portion of a Database Manipulation Language(DML) that involves information retrieval

Question 10

Definition

Data Manipulation Language (DML)

Answer 10

Data Manipulation Language (DML)

A language that enables users to access or manipulate data

Question 11

Data Manipulation Languages:

Two Types

Answer 11

• Procedural DMLs
  
  • Require user to specify what data is needed
  • Also how data should be retrieved
• Declarative DMLs
  
  • Only requires user to specify what data is needed
  • Does NOT require user to specify how to get it
  • Easier to learn than Procedural DMLs
  • Also called “Nonprocedural” DMLs

Question 12

Two Language Types

in a Database System

Answer 12

• Data Definition Language
  
  • Specifies the database schema
• Data Manipulation Language:
  
  • To express database queries and updates
• In practice, these are combined into a single database language, such as SQL

Question 13

Relational Data Model

Overview

Answer 13

• Uses a collection of tables to represent both
  
  • data
  • relationships among the data
• Each column(attribute) has a unique name (“name”, “phone”, “student_id”, etc)
• Tables are also known as Relations
• Is an example of a Record-Based Model
• This is the most widely used Data Model

Question 14

Definition:

Data Model

Answer 14

Data Model

A collection of conceptual tools for describing:

• data
• data relationships
• data semantics
• consistency constraints

Provides a way to describe the design of a database at each level:

• physical
• logical
• view

Question 15

Entity-Relationship(ER)

Data Model

Overview

Answer 15

• Uses a collection of basic objects:
  
  • Entities
  • Relationships
• An Entity is a thing or object in the real world, distinguishable from other object
• Entities have Relationships with other Entities
• Widely used model in database design

Question 16

Object-Based Data Model

and

Object-Relational Model

Answer 16

• Extends the E-R model with notions of:
  
  • Encapsulation
  • Methods(functions)
  • Object Identity
• Works with principles of Object-Oriented Programming
• There is also the Object-Relational Data Model, which combines features of the Object-Oriented and Object-Relational data models

Question 17

Semi-Structured Data Model

Answer 17

• Permits the specification of data where individual data items of the same type may have different sets of attributes
• This is in contrast to the other data models, where all objects of a type have the same attributes
• Widely uses Extensible Markup Language(XML) or similar to represent semistructured data

Question 18

Data Models:

4 Categories

Answer 18

• Relational Model
• Entity-Relationship Model
• Object-Based Data Model
• Semi-Structured Data Model

Question 19

Types of Schemas in a Database

Answer 19

• Schema:
  
  • The overall design of the database
• Subschemas:
  
  • Designs of different views at the View Level
• Logical Schema:
  
  • Design of the database at the logical level
• Physical Schema:
  
  • Design of the database at the physical level

Question 20

Disadvantages of

Conventional

File Processing Systems

Answer 20

• Data Redundancy/Inconsistency
  
  • Over time, various files will be used with different structures, same data will be stored, etc
• Difficulty Accessing Data
  
  • Unanticipated forms of data request require new programs or manual sorting
• Data Isolation
  
  • Data gets scattered in different files or formats
• Integrity Problems
  
  • Difficult to integrate new constraints
• Atomicity Problems
  
  • hard to implement atomic transactions
• Concurrent Access Anomalies
  
  • Multiple users may be able to access data simultaneously
• Security Problems
  
  • Not every user should have access to all data