normalisation

Question 1

what are the alternative names for a table ?

Answer 1

entity and relation

Question 2

what are the alternative names for a record ?

Answer 2

row entity instance

Question 3

what is the alternative name for a field

Answer 3

attribute, column, and property

Question 4

what is a relational datebase

Answer 4

the databases consist of many tables that contain s data that is related in some way.
these databases are called relational databases and are managed by the Database Management Systems (DBMS).

Question 5

what is a primary key

Answer 5

a field in a table that uniquely identifies each record in the table

Question 6

what is an easy way to make a primiary key

Answer 6

add an extra auto-numbered field to make each record unique

Question 7

what is a super key

Answer 7

a comnination of fields in a table which uniquely identify each row

Question 8

what is a candidate key

Answer 8

they are minimal super-keys and they are possible options for primary key s

Question 9

what is normalisation

Answer 9

the process of representing a problem in the real word as a set of tables

Question 10

what does normalisation avoid

Answer 10

repeating groups 
data redundancy 
anomalies :
  update 
  insertion
  deletion 
complex queries

Question 11

what is data redundancy ?

Answer 11

expanding the primary key produces data redundancy is when one field has two values like a name and a surname in the name field

Question 12

what is an update anomaly

Answer 12

when the same data needs to be updated in more than one place

Question 13

what is deletion anomaly

Answer 13

when deletion cause unecessary loss of data

Question 14

what is an insertion anomaly

Answer 14

when records are added that do not satisfy the primary key requirements

Question 15

what are the characteristics of first normal form

Answer 15

no repeating groups

choose a primay key

Question 16

what are the characteristics of second normal form

Answer 16

relation is in 1NF

no partial dependencies

Question 17

what are the characteristics of third normal form

Answer 17

relation is in 2NF and no transitive dependencies

Question 18

what is a partial Dependency

Answer 18

when a field’s walue is dependent on only part of composite key

Question 19

what is transitive dependency

Answer 19

when a field is dependent on a non- key field

Question 20

what is derived data

Answer 20

when you use field to calculate antoher like deriving a person’s age from their date of birth

Question 21

what is duplicate data

Answer 21

when a record has the same value for a field as another record

Question 22

what is atomic data

Answer 22

each value of a field should store a single datqa item and should no be combined

Question 23

what is referential Integrity

Answer 23

the idea that you can have data that refers to other data that does not exist

Question 24

what is an example one to one relationship

Answer 24

an example would be one teacher to a register class

Question 25

what is an example of a one to many relationship

Answer 25

would be a house to students there is one house and many students

Question 26

what is an example of many to many

Answer 26

that would be doctor to patient

Question 27

how to identify different tables

Answer 27

each table shold respresent an entity or a subject then each table should have a primary key. Then link the table using the primary and foreig keysthe rule is that the table on the many side gets the primary key of the one side of the relationship

Question 28

give a summary of the relationship rules

Answer 28

one to one: put both fields in the same table
one to many: add a foriegh key to the table on the many side which the primary key of the table on the one side
many to many: Create a new link table with a combination primary key using the primary key of the other two tables

Question 29

how do you ensure regerential Integrity?

Answer 29

we need to ensure queries cannot be performed that will violate the integrity of the database