Consider a relation representing the present position of molecules in a closed c
ID: 3662330 • Letter: C
Question
Consider a relation representing the present position of molecules in a closed container. The attributes are the ID for the molecule, the X, Y, and Z coordinates of the molecule, and its velocity in the X, Y, and Z dimensions. Refer to the X, Y, and Z coordinates as P_X, P_Y, and P_Z respectively, and the X, Y, and Z velocities as V_X, V_Y, and V_Z respectively.
a) What functional dependencies do you expect to hold?
b) What are the keys?
c) Other than the keys list three superkeys.
d) Other than the keys how superkeys are there?
Explanation / Answer
As given in the question
P_X,P_Y,P_Z are the coordinates of the molecule and V_X,V_Y,V_Z are the velocities of the correpnding coordinates.
a) P_X,P_Y,P_Z -> V_X,V_Y,V_Z and P_X,P_Y,P_Z -> molecule.
above functinal dependencies are the valid and we can write the their valid combination of the keys except transitives dependencies.
b) P_X,P_Y,P_Z and V_X,V_Y,V_Z are the keys because with these combination only we can get the molecule in the closed surface.
c) P_X,V_X,V_Y,V_Z P_Y,V_X,V_Y,V_Z P_Z, V_X,V_Y,V_Z etc.. are the super keys.
d) Super keys are used to get the all other attrbutes in the relation with one super key, that way they become the super keys.