Jul 20, 2014 · A superkey of a table T is a set of columns that functionally determines every attribute. A candidate key (CK) is a superkey that contains no smaller superkey. We can pick one CK as primary key (PK) and then call the other CKs …

Jan 5, 2017 · For a relation R, FD X->Y, holds true for relation R if and only if whenever two tuples of R have the same value of X, they also have the same value for Y. X and Y are a subset of attributes of R. This does mean X is a superkey, it is possible two tuples exist with the same X …

May 17, 2013 · superkey: a set of attributes which will uniquely identify each tuple in a relation. candidate key: a minimal superkey. primary key: a chosen candidate key. secondary key: all the rest of candiate keys. prime attribute: an attribute that is a part of a candidate key (key column) nonprime attribute: a nonkey column

May 9, 2015 · I am trying to find the superkeys of this relation, but I am having troubles finding out how many superkeys there are and exactly what they are. I figured out that the candidate keys were {A},{B},{...

If I design a database with a securitymaster table that has all the common columns and then have a final column called securitytype which acts as a reference to the sub table, how is it possible to

May 19, 2016 · I'm going though some past papers for my database exam and it asks: Specify all minimal keys for R R(A,B,C,D,E) A → B CD → E E → A B → D I am unsure what is ...

Jan 28, 2015 · The union between A and B is a superkey. (A candidate key is a superkey but a superkey could be not a candidate key) Moreover, remember that a candidate key is a particular type of superkey, so you shouldn't worry about if it is "both" key and superkey.

I got this result by trying out the combinations DA, DB, DC, DE and finding that only DE is the superkey. I'm curious whether my way to directly check if this relation is in BCNF is correct (I don't want to test for 3NF/2NF).

A superkey (and therefore a candidate key) that does not contain all attributes must contain at least an attribute set that is the left side of a functional dependency. Otherwise it would not be possible to generate an additional attribute from the attribute set of this superkey and this contradicts the definition of a superkey.

Jan 9, 2017 · X is a superkey or; Y is a member of a key. In the second case, since every key in R is simple, Y is itself a key, which implies that X is a superkey. Therefore, X -> Y does not violate BCNF in either case, which implies that R is in BCNF. I understand everything except the final part; Y being a key implies X being a superkey.