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I have this table that the rules are: A student is examined in a discipline and obtains a position on the class list. It is known that two students cannot obtain the same position in the same subject. Is this a 3NF database or BCNF, i cant have a 100% sure answer to this

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philipxy
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Young JooJ
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    Please [use text, not images/links, for text--including tables & ERDs](https://meta.stackoverflow.com/q/285551/3404097). Use images only for what cannot be expressed as text or to augment text. Include a legend/key & explanation with an image. – philipxy Dec 12 '20 at 21:46
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    Right now you are just asking for us to rewrite your textbook with a bespoke tutorial & do your (home)work & you have shown no research or other effort. Please see [ask], hits googling 'stackexchange homework' & the voting arrow mouseover texts. Show the steps of your work following your textbook with justification & ask 1 specific question re the first place you are stuck. Quote the definitions, theorems, algorithms & heuristics you are relying on. All the steps are also SO faqs. – philipxy Dec 12 '20 at 21:47

1 Answers1

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-- Student STUDENT examined in course COURSE
-- obtained position POSITION on class list.
--
test {STUDENT, COURSE, POSITION}
 KEY {STUDENT, COURSE}
 KEY {COURSE, POSITION}

Nontrivial FDs:

{STUDENT, COURSE}   --> {POSITION}
{COURSE, POSITION}  --> {STUDENT}

Use this as a quick check for NF:

---------------------------------------
For each nontrivial |
    FD X --> Y      |
at least one holds  | 2NF   3NF   BCNF
---------------------------------------
X is a superkey        ✔     ✔     ✔

Y is a subkey          ✔     ✔

X is not a subkey      ✔
---------------------------------------

FD X --> Y is trivial iff Y ⊆ X

For both nontrivial FDs X is a superkey; BCNF.

Damir Sudarevic
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