[Tutor] basic gadfly question

[Cynic]

>A relation is in third normal form (3NF) if and only if it is 
>in 2NF and every nonkey attribute is nontransitively dependent 
>on the primary key.

So, as you can see, NULLs actually break normalization rules.

At 21:45 11.6. 2001, Deirdre Saoirse Moen wrote the following:
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>This is *completely* untrue.
>
>In fact, if you actually READ Codd & Date, you'll discover why supporting null values is a requirement for a truly relational database.
>
>Why? Because sometimes there isn't a relationship between a record in one entity and another entity. And sometimes there is.
>
>For example, a student relation may have a link to a faculty relation only if the student has an advisor. If that student doesn't have an advisor, that attribute SHOULD be null.
>
>In a truly relational database, the null value would signify there was no relationship, which is correct.
>
>If you don't support nulls, you'd have to create a false value to a false record in the other relation, which implies a relationship that doesn't in fact exist.
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cynic@mail.cz
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