This is ECB’s chief economist Peter Praet in an interview with Les Echos:

 “Normally, a fall in prices would be able to support purchasing power and, therefore, domestic demand. But demand has remained weak, including in the biggest euro area economies”

It seems like Praet is not entirely sure about the difference between supply and demand shocks, but let me just illustrate the dffference in two graphs (I don’t have much time so I did it by hand and with the help of an iPhone…)

The European situation is the graph on the right.