TRAINING (SQL-1) - Database in general

Different Database Layers:
Most of relational databases have three layers (External, Logical & Physical layer).



What is Physical Data Independence in a database?
Ability to alter physical file structure of a database without disrupting existing users and process.
For example:
a.) Moving data file from one device or directory to another.
b.) Splitting or combining the data files.
c.) Renaming data files.
d.) Moving a database object from one data file to another.
e.) Adding new database objects or data files.

What is Logical Data Independence in a database?
Ability to make changes to the logical layer a database without disrupting existing users and process.
For example:
a.) Adding a new database object.
b.) Adding data items to an existing object.
c.) Alter existing database objects without impacting existing database objects.

What are conceptual database design components?
Below are the conceptual database design components:
a.) ENTITY = Table
b.) ATTRIBUTE = Column
c.) INSTANCE = Individual cell value of an ENTITY. For example individual EMPID.
c.) RELATIONSHIP = Cardinality
d.) BUSINESS RULES = Condition
e.) INTERSECTION DATA  = Common/intersaction data fetched from multiple tables.