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There are three very high-level classifications of constraints on data models in database conceptual design: inherent, explicit, and semantic.
Inherent means that the constrain can be fulfilled in the data model implicity.
Explicit means the constraint is fulfilled through a specific "Schema" of the model.
Semantic means the constraint would be fulfilled through application logic and cannot be satisfied within the model itself or any schema of the model.
These make sense in definition but I would appreciate some examples of each and an explanation of why the constrain can be made at the level where it is applied and not at the others.
Reference: https://cs.uwaterloo.ca/~tozsu/courses/CS338/lectures/3%20Constraints.pdf
This link provides a few examples but does not really explain the "Why" for each.
From the link
Constraints - Restrictions on the permitted values in a database state
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