Lecture 2

Question 1

data model is

Answer 1

a set of concepts that describes the structure of the database, the operations for manipulating these structures and certain constraints that the database should obey

Question 2

T or F

constraints specify some restrictions on valid data these constraints must be enforced at all time.

Answer 2

True

Question 3

Data model operations are

Answer 3

Operations are used for specifying database retrievals and updates by referring to the constraints of the data model

Question 4

operations may include

• ……. operations
• ……operations

Answer 4

basic model

user defined

Question 5

Categories of a data models

Answer 5

• conceptual (high level semantic)
  (provides concepts that are close the way many users can perceive data)
• physical (low-level internal) data model
  (provides concepts that describes details how data is stored in the computer implementations)
• Implementations (representational) data model
  (provides concepts that are intermediate between conceptual, physical)

Question 6

Now used data model is

Answer 6

relational model

Question 7

what is a database schema?

Answer 7

description of database, includes descriptions of the database structure and datatypes and the constraints on the database

Question 8

schema diagram is

Answer 8

an illustrative display that illustrates el description

Question 9

schema construct is

Answer 9

a component of the schema

Question 10

database state (instance)

Answer 10

actual data stored in database at a particular moment in time (occurrence, snapshot)

Question 11

does database state change with each transaction?

Answer 11

yes, that’s why it requires a time stamp

Question 12

what is an empty database state?

Answer 12

the beginning database after creation immediately with no data

Question 13

what is an initial database state?

Answer 13

refers to loading with the initial data into the system

Question 14

what is a valid state?

Answer 14

satisfies that structure and constraints (DBMS Is responsible for this)

Question 15

Schema VS State (changes perspective)

Answer 15

schema doesnt change frequently

state changes every transaction (every time the database is updated)

Question 16

what is the goal of three schema architecture?

Answer 16

to separate the user application from the physical database.

Question 17

DBMS three level

Answer 17

internal, conceptual, external schema

• internal : describe physical storage structure and access paths
• conceptual : describes the structure and constraints for the whole database for a community of users
• external: describes the various user views (the part that the user group is interested in )

Question 18

internal schema describes the structure and constraints ?

Answer 18

false , it describes physical storage structures and access paths

Question 19

conceptual schema describes the structure and constraints for the whole database?

Answer 19

true

Question 20

which schema level describes the various user views ?

Answer 20

external schema level

Question 21

which schema level describes the physical storage structure and access paths ?

Answer 21

internal schema level

Question 22

schema changes with the occurrence of each transaction ?

Answer 22

false, schema doesn’t change frequently

Question 23

name the categories or types of data models

Answer 23

• conceptual
• physical
• implementations

Question 24

data independence types

Answer 24

• logical

- physical data independence

Question 25

logical data independence is

Answer 25

capacity to change the conceptual schema without changing the external schema and their associated application programs (change el conceptual without the external ) - conceptual cared about the structure - external cared about user views

Question 26

physical data independence is

Answer 26

capacity to change the internal schema without having to change the conceptual schemas (change internal lw7do mn8yr conceptual) [internal describes the physical storage structure and access paths ]

Question 27

internal schema may be changed when certain file structures are reorganized?

Answer 27

yes, internal schema cares about physical storage structure so if you changed the file structure it will change.

Question 28

when a schema at the lower level is changed what is needed to be changed?

Answer 28

only the mapping between this schema and higher-level schema need to be changed in a DBMS

Question 29

if the lower level schema is changed then the application programs need to be changed

Answer 29

false, they needn't be changed since they refer to the external schema

Question 30

DBMS Languages

Answer 30

- Data Definition Language - Data Manipulation Language - Data Control language - Data retrieval languages

Question 31

Data Definition Language is used by

Answer 31

the DBA or Database designers

Question 32

DDL is used to

Answer 32

specify the conceptual schema of a database or the internal and external schemas

Question 33

Storage Definition language is used to

Answer 33

# define internal schema (realized via DBMS commands provided to the DBA and database designers)

Question 34

View Definition Language is used to

Answer 34

define external schema

Question 35

Data Manipulation Languages is used to

Answer 35

specify database retrievals and updates. - it's commands can be embedded in a general purpose programming

Question 36

Stand-alone DML Commands can be applied directly ( named?)

Answer 36

query language

Question 37

Types of DML

Answer 37

``` high level (non procedural) language low level (procedural) language ```

Question 38

the high level language is

Answer 38

set oriented and specify what data to retrieve rather than how to retrieve it can also be called declarative language

Question 39

the low language is

Answer 39

retrieves data one record at a time | constricts such as looping are needed to retrieve multiple records along with positioning pointers

Question 40

PL/SQL is considered a ... language (a) procedural (b) non procedural

Answer 40

(a) procedural, it is considered a low level language created by oracle

Question 41

DBMS interfaces examples

Answer 41

Stand-alone query language interfaces, programmer interfaces for embedding DML in programming languages , user-friendly interfaces, interfaces for the DBA

Question 42

Data Control Language is

Answer 42

roll back and commit