DBMS Intro.
Estimated reading time: 1 minuteDBMS
Database Management SYstem.
- table = entity
- column = attributes / fields
Main Theme of DBMS
- Abstraction
- Instance & Schema
Abstractions
Abstractions is a hiding process of irrelevant details. It has three steps
- Physical level (
making environment
) - Logical level (
type
) - view (
UI
)
Schema
Schema
is a design
or blueprint
of a database .
- Physical
- Logical
- View
database system
- table = entity
- columns = attributes
- rows = tuples
key
Key
uses for relational purpose or accessing unique row .
Primary key
Primary key
a set of column which describe unique row.
- underline
Super Key
Super key
is a set of one or more columns which describe unique row.
Candidate key
It is super key which ignore reduntant columns
Alternative key
Alternative key is aliasing process.
Composite key
Composite key is a set of column which describe unique rows.
Foreign key
Foreign key is a coulmn which point another table. You can compare is a passport
Relation
- one to one
- one to many
- many to one
- many to many
- polymorphic