Difference between Abstraction, Information hiding, Encapsulation

Difference between Abstraction, Information hiding, Encapsulation

An article by Edward V. Berard titled, "Abstraction, Encapsulation, and Information Hiding". 

(All citations are taken from the article mentioned above). Posting this here as I found useful and this may save your time of search in various websites.

Abstraction:

"One point of confusion regarding abstraction is its use as both process and an entity. Abstraction, as a process, denotes the extracting of the essential details about an item, or a group of items, while ignoring the inessential details. Abstraction, as an entity, denotes a model, a view, or some other focused representation for an actual item."

Information Hiding:

"Its interface or definition was chosen to reveal as little as possible about its inner workings." — [Parnas, 1972b]

"Abstraction can be […] used as a technique for identifying which information should be hidden."

"Confusion can occur when people fail to distinguish between the hiding of information, and a technique (e.g., abstraction) that is used to help identify which information is to be hidden."

Encapsulation:

"It […] refers to building a capsule, in the case a conceptual barrier, around some collection of things." — [Wirfs-Brock et al, 1990]

"As a process, encapsulation means the act of enclosing one or more items within a […] container. Encapsulation, as an entity, refers to a package or an enclosure that holds (contains, encloses) one or more items."

"If encapsulation was 'the same thing as information hiding,' then one might make the argument that 'everything that was encapsulated was also hidden.' This is not obviously not true."

Conclusion:

"Abstraction, information hiding, and encapsulation are very different, but highly-related, concepts. One could argue that abstraction is a technique that help us identify which specific information should be visible, and which information should be hidden. Encapsulation is then the technique for packaging the information in such a way as to hide what should be hidden, and make visible what is intended to be visible."

Go to the source! Grady Booch says (in Object Oriented Analysis and Design, page 49, second edition):

Abstraction and encapsulation are complementary concepts: abstraction focuses on the observable behavior of an object... encapsulation focuses upon the implementation that gives rise to this behavior... encapsulation is most often achieved through information hiding, which is the process of hiding all of the secrets of object that do not contribute to its essential characteristics.

In other words: abstraction = the object externally; encapsulation (achieved through information hiding) = the object internally