Subkeys

You are given the following table, with data, that identifies works of classical music that are in a CD or MP3 library. Draw the relation scheme for a lossless join decomposition of this table. You may assume that composer names are unique.

Compositions title composer nationality yearOfBirth Symphony #9 Beethoven German 1770 Violin Concerto Beethoven German 1770 Violin Concerto Brahms German 1841 Symphony #9 Shostakovich Russian 1906 Clarinet Concerto Mozart, W.A. German 1756 Symphony #9 Dvorak Czech 1841

First, look one-by-one at each attribute:

If I know the value of title, what (if anything) else do I know?

composer?

nationality?

year of birth?

Try it the other way: What other attribute(s) will tell me the value of:

title?

composer?

nationality?

year of birth?

title and composer?

nationality and year of birth?

all four attributes in the table?

Is there a candidate key for the whole table? If so, what is it?

Is there a subkey? Is so, what is it and why?

Now draw the revised relation scheme.