4 Normalisation Flashcards
(10 cards)
Can you describe any properties a relation must conform to?
They must have rows and columns
Each row describes a single entity of a replation. No duplication of rows are allowed
Each attribute is represented by a distinct column name
Each table must have a single attribute that can uniquely identify each row
Provide a defenition for full functional dependency…
when one attribute in a relation uniquely determines another attribute.
This can be written A -> B which would be the same as stating “B is functionally dependent upon A.”
Provide a defenition for full functional dependency…
The dependent attribute depends on all determinent attributes
What is a null value?
Means no data entry!/ Cant be used a s aprimary key.
Should be avoided as they are unknown attribute values.
In the Date-Codd notation. What is a constraint?
A constraint can be described as a “standard datatype”.
E.g: intger, string, date, true/false, float
State some key rinciples of Non Loss decomposition (Normalisation)…
Dont delete any attributes- Move them into new relations instead.
Must maintain relationships by preserving foreign keys
What is Non Loss decomposition (Normalisation)?
Stripping down a relation into its essential attributes
Usually results in more relations with fewer attributes
Aim for 3NF!
What is 1NF?
No repeating groups in a table
All non primary key attributes are functionally dependent on primary key
Must not contain duplicate rules
What is 2NF?
In 1NF & move everything that is not fully functional dependent into a seperate relation together with the determining key. Keep the origional relation less the removed dependent attributes
What is 3NF?
It is in 2NF - Check every non-primary key attribute depends only on the primary key
Search for issues wehere something is acting as the primary key!
