Database 2

Question 1

what is un-normalised data?

Answer 1

its characterised by redundancy and inconsistencies, there are repeated fields and multiple values of attributes

Question 2

what is normalised data?

Answer 2

it involves the application of a set of rules to remove undesirable characteristics and problems and can be used to test the correctness of an ER model.

Question 3

1NF?

Answer 3

all attributes are atomic and entities do not have repeating groups

Question 4

2NF?

Answer 4

it fulfils the conditions of 1NF and all non-key attributes in the relation are fully dependent on the primary key

Question 5

what are non-key attributes?

Answer 5

they are only partially dependent on the key are removed to a new entity along with a copy of their determinant

Question 6

3NF?

Answer 6

as long as an attribute does not depend on another attribute which is not the primary key- this is called transitive dependency

Question 7

advantages of normalisation

Answer 7

it will take up less storage because the duplicated data will be minimised

information retrieval will be more efficient because data is structured effectively- will be processed faster

less redundancy means less inconsistencies in data because only have been entered once

data integrity will be increased

Question 8

disadvantages of normalisation

Answer 8

its a complex process required to create the database structure

can generate more tables than an un-normalised database

slow to run due to complex database and queries

its necessary to assign more relationships to interact with larger numbers of tables

Question 9

what is a data dictionary?

Answer 9

its a file containing descriptions of the structure of the data stored in a database