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Relational Model - Coggle Diagram
Relational Model
each RELATION
has
TUPLE
is also known as a ROW
ATTRIBUTE
is also known as a COLUMN
is
ATOMIC
Single data value
INTEGRITY CONSTRAINS
Each TUPLE is UNIQUE and is identified by a KEY
There a different types of KEYS and they are known as
PRIMARY KEY
The main Key or UNIQUE IDENTIFIER of the the table
FOREIGN KEY
The key used to reference the PRIMARY KEY from another Table
CANDIDATE KEY
A minimal SUPER KEY
ALTERNATE KEY
any candidate key that is not chosen as the primary key of the relation
SUPER KEY
Combination of Attributes containing unique values
DATA INTEGRITY CONSTRAINTS
DOMAIN CONSTRAINTS
Applies to values of an attribute
Specifies that...
Each attribute within a relation must be from a single domain
The domain of an attribute limits its data to particular set of allowable values
Domains are more than just data type, as they indicate the meaning of the data
ENTITY INTEGRITY CONSTRAINTS
applies to a SINGLE relation...
PRIMARY KEY cannot be NULL
PRIMARY KEY must be UNIQUE
REFERENTIAL INTEGRITY CONSTRAINT
applies to a TWO relations
If a foreign key exists in a relation, its value must either refer to an existing record in the relation it references
ENTERPRISE CONSTRAINTS
are additional constraints that apply to the particular system being modelled....
specified by the users of the system, rather than the requirements of the relational model
Example...
A student must have passed the prerequisite for a unit before enrolling in it
A student must have passed 18 points at Part 1 before enrolling in a Part 2 unit
NORMALISATION