databases

Question 1

what is an entity

Answer 1

an item of interest about which information is stored

Question 2

what is a relational database

Answer 2

a database that recognises the difference between entities by creating different tables for each entity

Question 3

what are attributes

Answer 3

characteristics of the entity
categories about which data is collected

Question 4

what is a flat file

Answer 4

a database that consists of a single file
most likely be based around a single entity and its attributes
Entity1(Attribute1, Attribute 2…)

Question 5

what is a primary key

Answer 5

unique identifier for each record in the table
usually underlined

Question 6

what is the foreign key

Answer 6

the attribute that links two tables together
exist in one table as the primaryy key and act as a foreign key in another

Question 7

what is a sechondary key

Answer 7

allows the database to be searched quickly

Question 8

what are the 3 different entity relationship models

Answer 8

1 - 1
1 - many
many - many

Question 9

1 - 1

Answer 9

each entity is linked to one other entity

Question 10

1 - many

Answer 10

1 table is associated with many other tables

Question 11

many - many

Answer 11

1 entity can be associated with many other entities

Question 12

what is normalisation

Answer 12

the process of coming up with the best possible layout for a relational database

Question 13

what does normalisation try to accomplish

Answer 13

no redundancy
consistent data throughout linked tables
records can be added and removed without issues
complex queries can be carried out

Question 14

what are the 3 types of normalisation

Answer 14

1st normal form
2nd normal form
3rd normal form

Question 15

first normal form

Answer 15

there must be no attribute that contains more than a single value

Question 16

second normal form

Answer 16

a database which doesnt have any partial dependancies and is in first normal form can be said to be in second normal form. This means that no attributes can depend on part of a composite key

Question 17

third normal form

Answer 17

if the database is in second normal form and contains no non key dependancies its in 3rd normal form

Question 18

what is a non key dependancy

Answer 18

it means that the attribute only depends on the value of the primary key and nothing else

Question 19

what is indexing

Answer 19

a method used to store the position of each record ordered by a certain attribute
used to look up and access data quickly

Question 20

why are primary keys not used for indexing

Answer 20

although its automatically indexed its not normall remembered so secondary keys are used

Question 21

3 types of capturing data

Answer 21

magnetic ink character recognition
optical mark recognition
optical character recognition

Question 22

magnetic ink character recognition

Answer 22

all the details excluding the amount are printed in a special magnetic ink which can be recognised by a computer but the amount must be entered manually

Question 23

optical mark recognition

Answer 23

used for multiple choice questions on a test

Question 24

exchanging data

Answer 24

process of transferring the collected data

Question 25

what is a way of exchanging data

Answer 25

electronic data interchange
doesnt require human interaction and enables data trasnfer from 1 computer to another

Question 26

sql method

Answer 26

select, from, where, order by

Question 27

what does ORDER BY do

Answer 27

specifies if u want it in ascending or descending order

Question 28

what does JOIN do

Answer 28

method of combining rows from multiple tables based on a common field between them

Question 29

what does CREATE do

Answer 29

allows u to make new databases

Question 30

what does ALTER do

Answer 30

add, delete or modify the columns in a table

Question 31

what does INSERT INTO do

Answer 31

used to insert a new record into a database table

Question 32

what is referential integrity

Answer 32

process of ensuring consistency
ensures information isnt removed if required somewhere else in a linked database
if 2 tables are linked 1 cant be deleted cause the other requires its contents

Question 33

what does ACID stand for

Answer 33

Atomicity
Consistency
Isolation
Durability

Question 34

what is atomicity

Answer 34

a transaction must be processed in its entirety or not at all

Question 35

what is consistency

Answer 35

a transaction must maintain the referential integrity rules between linked tables

Question 36

what is isolation

Answer 36

simultaneous executions of transactions should lead to the same result as if they were executed one after the other

Question 37

what is durability

Answer 37

once a transaction has been executed it will remain so regardless of the circumstances, even if a power cut

Question 38

record locking

Answer 38

process of preventing simultaneous access to records in a database

Question 39

why is record locking used

Answer 39

to prevent inconsistencies or a loss of updates

Question 40

how does record locking work

Answer 40

while 1 person is editing the record it ‘locks’ so other ppl cant access the same record

Question 41

what is a problem of record locking

Answer 41

deadlock

Question 42

what is redundancy

Answer 42

process of having one or more copies of data in physically different locations
so if theres damage the others can be recovered