QUESTION $1$

Below is a list of database concepts. Your task is to contribute a SINGLE characteristic for ANY ONE concept, which can be one of the following, where applicable $($definition$,$ description, how it is used, etc.$).$ Your answer should be at least $120$ words.

Business rule

Entity integrity

Referential integrity

Total completeness

Partial completeness

Specialization

Generalization

Specialization hierarchy

Inheritance

Aggregation

Simple attribute

Primary key

Candidate key

Foreign key

Composite key

Superkey

Normalization

Atomicity

COMMIT command

Data dictionary

Equijoin

Left outer join

Right outer join

Predicate logic

INTERSECT operator

UNION operator

ROLLBACK command

ALTER TABLE command

$1$NF

$2$NF

$3$NF

$4$NF

BCNF

Entity subtype

Entity supertype

Surrogate key

Conceptual design

Conceptual schema

Data warehouse

Existence $-$dependent

Internal schema

Non$-$identifying relationship

Relational diagram

Single$-$valued attribute

Wildcard character