databases

Question 1

what is a

database

Answer 1

an organised collection of data

Question 2

organising

data in a database is

Answer 2

• easy adding
• ability to modify
• deletion
• searching

Question 3

electronic databases =

Answer 3

• easy to add, retrieve, delete, update and modify data
• easy to back up
• can be accesed by multiple poeple at the same time from different locations

Question 4

flat file

Answer 4

A flat file is a database that consists of a ​single file. The flat file will most likely be based around a single entity and its attributes

Question 5

advantages of

flat file

Answer 5

• quick to set up
• require little expertise to maintain
• suitable for small amounts of data

eg: storing contact detales, playlist

Question 6

drawbacks of

flat file

Answer 6

• take up uncessary space
• be slow to query
• become increasingly difficult to maintain

Question 7

relationship

Answer 7

• recognisesthe differences between entities by creating different tables for each entity
• need a common field for the relationship to work

the link between two tables

Question 8

Primary Key

Answer 8

A primary key is a unique identifier for each record in the table

Question 9

Foreign Key

Answer 9

A foreign key is the attribute which links two tables together. The foreign key will exist in one table as the primary key and act as the foreign key in another

Question 10

Secondary Key

Answer 10

A secondary key allows a database to be searched quickly

Question 11

One-to-one

Answer 11

Each entity can only be linked to one other entity

relationship between a husband and wife. 1 wife to 1 husband

Question 12

One-to-many

Answer 12

One table can be associated with many other tables, such as a mother having multiple children. Similarly, multiple child entities can be linked to the same mother entity.

Question 13

Many-to-many

Answer 13

One entity can be associated with many other entities and the same applies the other way round. An example is students and courses - each student can enrol in more than one course and each course can have more than one student.

Question 14

normalisation

Answer 14

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

Question 15

normalisation tries to acomplish:

Answer 15

No redundancy​ (unnecessary duplicates).
● Consistent data​ throughout linked tables.
● Records can be​ added and removed without issues.
● Complex ​queries ​can be carried out.

Question 16

first normal form (1NF)

Answer 16

There must be ​no attribute​ that contains ​more than a single value
1) all field names must be unique
2) values in feilds should be from the same domain
3) values in fields should be atomic (single value)
4) no two records can be identical
5) each table needs primary key

Question 17

second normal form (2NF)

Answer 17

1) already in 1NF
2) any partial dependencies have been removed

Question 18

to fix

many to many tables

Answer 18

1) create link tables
2) assigning the primary key from the two linking tables as the composite key from the new linking table
3) flip the M:M crows feet to become two 1:M relationships joined by the new table

Question 19

third normal form 3NF

Answer 19

1) data already in 2NF
2) any transitive dependances (non-key) has been removed

all keys are dependant on the key, the whole key and nothing but the key

Question 20

why should

all field names must be unique

1NF

Answer 20

to avoid confusion about which record should be retrieved or updated

Question 21

1NF

values in feilds should be from the same domain

because

Answer 21

each feild must contain the same type of data

Question 22

values in fields should be atomic (single value)

because

Answer 22

each field should only contain a single item of data

Question 23

1NF

no two records should be identical

because

Answer 23

duplicarte data take up space unnecisarly and can cause inconsistances if updates are not performed on all of them

Question 24

1NF

each table needs primary key

because

Answer 24

a field or several fields (composite key) that gives a record of a unique identity

Question 25

2NF

needs to already be in 1NF

Answer 25

a partial dependancy means one or more feilds depend on only part of the primary key

Question 26

2NF

remove of partial dependances

because

Answer 26

this sitch can occur if the primary key is a composite key comprised of more than 1 field

Question 27

2NF

fix any M:M relationships

because

Answer 27

we are aiming to make sure every table seves a single purpose

Question 28

3NF

remove any transitive dependances

Answer 28

to ensure that non-key fields are not dependant on each other