# Logical Data Modeling - Constraint

A constraint is a metadata rule that expresses a condition or restriction in natural language text or in a machine readable language for the purpose of declaring some data or process semantics.

## Example

• Structure: All rows must have the same number of columns
• Data domain: All value in a column must have the same type
• Relationship: A child cannot have three parents
• Business rule: A product cannot be send to a client that was not verified.

## Documentation / Reference

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