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Consider R: A B C D E F G H I J and given next dependecies:

CE -> J
J -> E 
CJ -> J 
CJ -> E
C -> D 
D -> J

I'm trying to figure out a dependencies tree. I suppose that CE -> J -> E is a redundant dependency so I can just delete that dependency. But can someone explain to me why? I'm not getting the ponit of not considering CE -> J -> E if J still needs CE to exist.

This is not a homework. Im just trying to get into db normalization.

philipxy
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myge32
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  • What is "a dependencies tree"? "delete that dependency"? "needs CE to exist"? We can guess, but you don't use proper terms or notions. (There's a dag, not a tree.) Follow a published academic textbook, because right now you are just asking us to rewrite one. Show the steps of your work with justification & ask 1 specific researched non-duplicate question re the 1st place you are lost/stuck. (Manuals for languages & tools to record & use designs are not such textbooks.) (Nor are wiki articles or web posts.) Dozens are online free in pdf & html. PS Steps are SO faqs; but SO answers are poor. – philipxy Jul 15 '20 at 05:18
  • What does "I have these FDs" mean? "These are all the FDs that hold"?--Not possible. "These are all the non-trivial FDs that hold"?--Not possible. "These are some FDs that hold"?--Maybe, but probably not. "These FDs hold & only the ones that hold when these do hold"? Maybe. What is your question? "What is the dag of all the FDs that hold when these do"? Maybe. Find out what a *closure*, a *cover* & a *minimal cover* are & what your question is using appropriate terms. [See this answer.](https://stackoverflow.com/a/53386492/3404097) – philipxy Jul 15 '20 at 05:31

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