Apologies if there is an obvious answer to this...

My question concerns how Wolfram Alpha determines what is a function and what is a simple variable. In particular:

if I enter:

D[x^2*y^2,y] 

I get the partial derivative with respect to $y$ - i.e.

2x^2y

If I enter:

D[x^2*y^2,y],D[x^2*y^2,x] 

I get both partial derivatives - i.e.

2x^2y and 2xy^2.

However if I just enter:

D[x^2*y^2,x]

then it assumes that $y$ is a function of $x$ and I get the answer:

d/dx(x^2 y^2) = 2 x y (x y'(x)+y).

Is there some way to control this behaviour - e.g. in this case if I enter something like

D[x^2*y^2,x]

make the system assume $y$ is a variable and not a function.