Question regarding 2NF partial key dependency
Assuming your relation is ABCD and assuming you meant the following functional dependencies:


AB-->C
BC-->D


Then you need to decompose this relation to get it to third normal form (3NF).  This is because D is not determined by the key of ABCD.  To bring this to 3NF you need to have two relations: ABC and BCD.  Now each non-key attribute is fully dependent on the key of its relation (and nothing else).