Data science produces insights
Data science is distinguished from the other two fields because its goal is an especially human one: to gain insight and understanding.
This definition of data science thus emphasizes:
Machine learning produces predictions
I think of machine learning as the field of prediction: of “Given instance X with particular features, predict Y about it”. These predictions could be about the future (“predict whether this patient will go into sepsis”), but they also could be about qualities that aren’t immediately obvious to a computer (“predict whether this image has a bird in it”). Almost all Kaggle competitions qualify as machine learning problems: they offer some training data, and then see if competitors can make accurate predictions about new examples.
Artificial intelligence produces actions
Artificial intelligence is by far the oldest and the most widely recognized of these three designations, and as a result it’s the most challenging to define. The term is surrounded by a great deal of hype, thanks to researchers, journalists, and startups who are looking for money or attention.