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Updated Thu, 07 Jul 2022 00:41:25 GMT

Must tuples of a relation and their referents be in a one-to-one relationship?


Figures 3.a and 3.b, section 1.4, page 381 of Edgar Codds 1970 landmark paper A Relational Model of Data for Large Shared Data Banks presents a set of relation schemas (unnormalized in figure 3.a and in 1NF in figure 3.b).

First normal form.

The normalized relation schema children has a key dependency KEY(man#, childname), so it allows instances like the following relation:

man# childname birthdate
1 "Thomas" 2016-03-12
2 "Paul" 2011-08-02
2 "Julia" 2012-01-25
3 "Thomas" 2016-03-12



Solution

Does the relational model mandate that the relationship between tuples of a relation and their referents be one-to-one

No. The relational model only manages the tuples. The mapping of a tuple to an assertion in some real-world domain, or some tangible external thing is not governed by the rules of the relational model.

Moreover, in your example the relation children doesn't model actual children, it models the relationship between an employee and a child. The relevant fact being modeled is only the number and ages of each employee's children.

You could add a separate table with one row per actual child, but that would simply be a different model, not a more correct one.







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