Determining Transitive Dependencies
A FD (functional dependency) X -&gt; Z is transitive when there exists a Y such that X -&gt; Y AND Y -&gt; Z AND NOT Y -&gt; X AND NOT Y = Z. (X, Y &amp; Z are attribute sets.)
There can be lots of X, Y &amp; Zs where X -&gt; Y AND Y -&gt; Z but X -&gt; Z is not transitive because Y -&gt; X. Eg this happens whenever X and Y are CKs (candidate keys). (Because CKs functionally determine all attributes--each determines the other and Z.) And there can be lots of transitive FDs. Eg this happens whenever there is a FD whose attributes are non-prime. (Because a CK determines that FD's determinant which itself doesn't determine the CK--if it did then it would be a CK, which with non-prime attributes it isn't.) The FDs among all those ones that are important for normalization are transitive FDs of non-prime attributes on CKs when a relation is in 2NF. Because it is always possible to losslessly decompose such a relation to components free of them, ie in 3NF.