((attr1,attr2), label) -----> ( (-1,1),1); ((1,-1),1),((1,1),1),(-1,-1),-1).
So bottom left is -1, rest +1.
I think you need to use more data points.
There are many more functions that can fit these 4 data points perfectly,
other then the function f(x,y) = positive(x) or positive(y).
Also, it is important use use labels like a, b, instead of 1, -1, else its not a classification problem, but a regression problem.
You seem to want to find a function that is something like
y(x) = x - 1.
and then f(x,y) = y(x) > 0?