Databases

Question 1

data elements

Answer 1

facts that represent real-world information

Question 2

database

Answer 2

a shared collection of related data used to support the activities of a particular organization

Question 3

database management system (DBMS)

Answer 3

a collection of programs that enables users to create and maintain databases and control all access to them

Question 4

table

Answer 4

a combination of fields

Question 5

concurrency control strategies

Answer 5

These strategies ensure that the data accessed are always correct and that data integrity is maintained

Question 6

database constraint

Answer 6

restriction or rule that dictates what can be entered or edited in a table

Question 7

Data type

Answer 7

the sort of data permitted in a field

Question 8

Data uniqueness

Answer 8

uch as the primary key ensures that no duplicates are entered

Question 9

concurrency control subsystems

Answer 9

This feature ensures that data remains consistent and valid during transaction processing even if several users update the same information

Question 10

metadata

Answer 10

defines and describes the data and relationshipsbetween tables in the database

Question 11

self-describing

Answer 11

a database system is referred to as self-describing because it not only contains the database itself, but also metadatawhich defines and describes the data and relationships between tables in the database

Question 12

entity

Answer 12

attributes that represent properties such as an employee’s name, address and birthdate

Question 13

relationship

Answer 13

represents an association among entities

Question 14

entity relationship model

Answer 14

uses main concepts like entities, attributes and relationships. An entity represents a real-world object such as an employee or a project.

Question 15

Record-based logical data models

Answer 15

Three well-known data models of this type are relational data models, network data models and hierarchical data models.

Question 16

relational model

Answer 16

represents data as relations, or tables

Question 17

network model

Answer 17

represents data as record types. This model also represents a limited type of one to many relationship called a set type

Question 18

hierarchical model

Answer 18

represents data as a hierarchical tree structure

Question 19

relation

Answer 19

another term for table

Question 20

set type

Answer 20

a limited type of one to many relationship

Question 21

The goal of the data modeling phase is to describe

Answer 21

• The data contained in the database
• The relationships between data items (e.g., students are supervised by lecturers; lecturers teach courses)
• The constraints on data (e.g., student number has exactly eight digits; a subject has four or six units of credit only)

Question 22

database design

Answer 22

two sub-steps: one called database logical design and another called database physical design

Question 23

database logical design

Answer 23

defines a database in a data model of a specific DBMS

Question 24

database physical design

Answer 24

defines the internal database storage structure, file organization or indexing techniques.

Question 25

data model

Answer 25

collection of concepts or notations for describing data, data relationships, data semantics and data constraints

Question 26

External models

Answer 26

Represent the user’s view of the database Contain multiple different external views Are closely related to the real world as perceived by each user

Question 27

Conceptual models

Answer 27

Provide flexible data-structuring capabilities Present a “community view”: the logical structure of the entire database Contain data stored in the database Show relationships among data including: Constraints Semantic information (e.g., business rules) Security and integrity information Consider a database as a collection of entities (objects) of various kinds Are the basis for identification and high-level description of main data objects; they avoid details Are database independent regardless of the database you will be using

Question 28

Internal models

Answer 28

The three best-known models of this kind are the relational data model, the network data model and the hierarchical data model. These internal models: Consider a database as a collection of fixed-size records Are closer to the physical level or file structure Are a representation of the database as seen by the DBMS. Require the designer to match the conceptual model’s characteristics and constraints to those of the selected implementation model Involve mapping the entities in the conceptual model to the tables in the relational model

Question 29

Physical models

Answer 29

Are the physical representation of the database Have the lowest level of abstractions Are how the data is stored; they deal with Run-time performance Storage utilization and compression File organization and access methods Data encryption Are the physical level – managed by the operating system (OS) Provide concepts that describe the details of how data are stored in the computer’s memory

Question 30

logical design

Answer 30

Once a DBMS is selected, you can then implement it. This is the internal model. Here you create all the tables, constraints, keys, rules, etc.

Question 31

schema

Answer 31

is an overall description of a database, and it is usually represented by the entity relationship diagram (ERD)

Question 32

External schemas

Answer 32

there are multiple

Question 33

Multiple subschemas

Answer 33

these display multiple external views of the data

Question 34

Conceptual schema

Answer 34

there is only one. This schema includes data items, relationships and constraints, all represented in an ERD

Question 35

Physical schema

Answer 35

there is only one

Question 36

Data independence and operation independence together form

Answer 36

data abstraction