In what way is Data Hiding related to Data Abstraction?

Data Hiding and Data Abstraction are complementary concepts. Data Abstraction focuses on the observable behaviour of an object, whereas Data hiding or Data Encapsulation focuses upon the implementation that gives rise to this behaviour. In other words, Data Abstraction cares about what something does but not how it does it. Data Encapsulation cares about how something does what it does such that others don't have to worry about the implementation details. Hence, we can say that Encapsulation is a way to implement Data Abstraction.