chapter 6

Question 1

what is a simple UID

Answer 1

A UID that is a single attribute is a simple UID

Question 2

what is a composite UID

Answer 2

If the UID is a combination of attributes, it is called composite UID

Question 3

what is a UID

Answer 3

It is the value or combination of values that enables the user to find that one unique item among all the rest.

Question 4

What are artificial UID

Answer 4

• -> dont occur in the natural world but are created for purposes of identification in a system
• -> people are not born with numbers, but a lot of systems assign unique numbers to identify people

Question 5

A UID can be both _____ and ______

Answer 5

artificial and composite

Question 6

Sometimes the UID is a combination of both _________ and a _________

Answer 6

attribute and a relationship

Question 7

what can be used instead of a barred relationship to the originating entities

Answer 7

Intersection entity

Question 8

What is a candidate entity

Answer 8

• -> sometimes 2 or more UIDs exist
• -> these are both candidate UIDs
• -> only one of the candidate UIDs is chosen as the actual UID which is called primary UID
• -> the other UIDs are called secondary UID

Question 9

example of candidate UID

Answer 9

student ID and badge number

• -> student ID is the primary UID
• -> badge number is a secondary UID

Question 10

what does a primary key allow you to do

Answer 10

access a specific record in teh database

Question 11

There is not limit to the number of attributes that can make up a UID

Answer 11

True

Question 12

do you need the barred relationship if you have an artificial UID

Answer 12

no barred relationships required

Question 13

what is the normalisation process

Answer 13

Database normalisation is a database schema design technique, by which an existing schema is modified to minimise redundancy and dependency of data.

Normalization splits a large table into smaller tables and defines relationships between them to increase the clarity in organizing data.

Question 14

what is the first normal form

Answer 14

• -> the first normal form requires that no multi-valued attributes exist
• -> to check for 1NF, validate that each attribute has a single value for each instance of the entity

Question 15

how to convert into first normal form

Answer 15

if an attribute is multi valued, create an additional entity and relate it to the original entity with a 1:M relationship

Question 16

what is the goal of a database designer

Answer 16

store information in one place only and in the best possible way
this can be achieved by applying the rules of normalization

Question 17

what is the second normal form

Answer 17

the second normal form requires that any non-UID attribute be functionally dependent on all parts of the UID

*dont write 👇 (extra info)
however non-key columns can still be functionally dependent on other non key columns

Question 18

give an example where third normal form can help solve the problem

Answer 18

if you have several friends who go to the same school, and you enter the school’s street address along with each of them, you would not only be duplicating the data but cause potential problems such as for instance if the school moved and changed its address, you would have to go back and change it everywhere.

Question 19

what does the third normal form state

Answer 19

• -> no non-UID attribute can be dependent on another non-UID attribute
• -> third normal form prevents transitive dependencies
• -> a transitive dependency exists when any attribute in an entity is dependent on any other non-uid in that attribute

Question 20

give an example where the second normal form can help solve a problem

Answer 20

if you store a friend’s address in the recipe box you may not find it until you look up that recipe

Question 21

what is a prime attribute

Answer 21

An attribute, which is a part of the candidate-

key, is known as a prime attribute

Question 22

what is a non prime attribute

Answer 22

An attribute, which is not a part of the

prime-key, is said to be a non-prime attribute

Question 23

if we follow second normal form then ______________

Answer 23

If we follow second normal form, then every non-prime attribute
should be fully functionally dependent on prime key attribute.

Question 24

what is a transitive dependency

Answer 24

A transitive dependency exists when any attribute in an entity is dependent on any other non-UID attribute in that entity.

Question 25

what is another way of stating the third normal form

Answer 25

A non UID attribute cannot have attributes of their own

Question 26

what is a. superkey

Answer 26

it is a set of columns such that the value of that set of columns is unique across various rows