normalisation

Question 1

relational database

Answer 1

consists of many tables w many records w many fields where field stores single data item
relation/entity- table
row/entity instance - record
attribute/column/property - field
primary key underlined

managed by database management systems (dbms)

Question 2

primary key fiels

Answer 2

uniquely identifies each record on table
no data value in primary key field is repeated
can be made by adding extra auto-numbered field so each record is made unique
naming convention- tablenameID

Question 3

super keys

Answer 3

combination of fields in table which uniquely identify each row

more than 1 field

Question 4

candidate keys

Answer 4

minimal super keys w no attributes included which do not contribute to uniqueness of rows

Question 5

composite/compound/concatenated keys

Answer 5

combo of 2 or more fields to form primary key

Question 6

normalisation

Answer 6

the process of organizing data in a database by creating tables and establishing relationships between those tables according to a defined set of rules designed both to protect the data and to make the database more flexible by eliminating redundancy and inconsistent dependency.
avoids repeating groups, data redundancy, anomalies (update,insertion,deletion)
complex queries

Question 7

repeating group

Answer 7

field that can have multiple values
when repeating groups are removed, data redundancy is produced
in normalised database - all fields should have single value

Question 8

anomalies

Answer 8

update anomaly- same data needs to be updated in more than one place
deletion anomaly- deletion causes unnecessary data loss
insertion anomaly- records are added that do not satisfy primary key requirements

Question 9

dependancies

Answer 9

1 field related to another
A ➔ B
B is determined by A

Question 10

partial dependancy

Answer 10

field’s value is dependent on part of a composite key

Question 11

transitive dependency

Answer 11

field’s value is dependent on non-key field

Question 12

derived data

Answer 12

use a field to calculate another
not stored

Question 13

duplicate data

Answer 13

record has same value for a field as another record
not wrong; not redundant

Question 14

atomic data

Answer 14

only storing single data item in single field

Question 15

referential integrity

Answer 15

you cannot have data that refers to other data that does not exits

Question 16

relationships

Answer 16

one to one (1:1): only 1 field matches 1 field, simple,both fields put in same table
1-1

one to many (1:n) 1 has many (1 class has many students)
1- ♾️

many to many (m:n)
♾️-♾️