Accessibility Modifiers

public
- Access is not restricted.
- Allows the members to be globally accessible.

protected
- Access is limited to the containing class or types derived from the containing class.

internal
- Access is limited to the current assembly.
- Internal members are accessible only within files in the same assembly.

protected internal
- Access is limited to the current assembly or types derived from the containing class.

private
- Access is limited to the containing type.

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sealed
- prevents inheritance

Sources: Accessibility Levels (MSDN), Difference between internal and private

1-2-3 Normal forms

1^st Normal Form – Eliminate Repeating Groups (ERG)
all occurrences of a record type must contain the same number of fields. No sets

2^nd Normal Form – Eliminate Redundant Data (ERD)
violated when a non-key field is a fact about a subset of a key.

3^rd Normal Form – Eliminate Columns Not Dependent on Key (ENDK)
violated when a non-key field is a fact about another non-key field.

All normal forms are additive.

Source