Chapter 17 - Relational databases and normalisation

Question 1

Where are data held in a relationship data base?

Answer 1

» Tables - also called relations

Question 2

What is a relational databse?

Answer 2

» Collection of tables in which relationships are modelled by shared attributes

Question 3

What does a row represent?

Answer 3

» One record

Question 4

What does a column represent?

Answer 4

» One attribute

Question 5

How would you describe a table?

Answer 5

» Entity name - shown outside the brackets
» Attributes - listed inside the brackets
» Primary key is underlined

Question 6

What is the purpose of the primary key?

Answer 6

» Unique identifer to identify a particular record in the table

Question 7

What is the purpose of indexing a primary key?

Answer 7

» So that a record with a particular primary key can be quickly located in a database

Question 8

What is the foreign key?

Answer 8

» Attribute which is a primary key of one of the tables - links tables together

Question 9

What is normalisation?

Answer 9

» Technique for designing a relational database to minimise duplocation of information and eliminates redunant data

Question 10

What are the 4 features of normalisation?

Answer 10

» No data is unncessarily duplicated
» Data is consistent
» Structure of each table is flexible enough to allow you to enter as much as you want
» Structure should enable a user to make all kind of compelx queuries

Question 11

How many normalisations are there?

Answer 11

» 4

Question 12

What are the 3 features of the first normal form (1NF)?

Answer 12

» Each data tem cannot be broken down any further
» Each row record has a primary key
» There are no repeating data

Question 13

What is the main thing to remember when some entities have a many-to-many relationship?

Answer 13

» You will always need a link table in the middle

Question 14

What are the features of the second normal form? (2NF)

Answer 14

» If it is in the 1NF
» Contains no partial dependencies

Question 15

What is a partial dependency?

Answer 15

» Mean that one or more of the attributes depends on only part of the primary, which can only occur if the primary key is a composite key

Question 16

What are the features in the third normal form (3NF)?

Answer 16

» It is in the 2NF
» Contains no non-key depedencies

Question 17

What is a non-key depedency?

Answer 17

» Where one value of an attribute is determined by the value of another attribute which is not part of the key

Question 18

What is the main principle in 3NF?

Answer 18

» All attributes are dependent on the key, the whole key, and nothing but the key

Question 19

What is an entity?

Answer 19

» A category of object of something or interest

Question 20

What is the one of the main aims of normalising data?

Answer 20

» Remove the possibility of redundant data from any of the tables

Question 21

What is redundant data?

Answer 21

» Data that appears in more than one database table
» Which can cause inefficiencies and inconsistencies in data

Question 22

What is mantained in a normalised database?

Answer 22

» Data integrity

Question 23

How can normalisation lead do faster sorting and searching?

Answer 23

» Normalisation will produce smaller tables, with fewer fields
» Leads to greater efficiency, as there is less data involved

Question 24

What are the 3
benefits of normalisation?

Answer 24

» No unecessary duplication of data
» Data integrity is maintained
» Fewer fields - faster searches

Question 25

What is atomic?

Answer 25

» Data cannot be broken down any further