Abstraction

Computer programming is full of abstractions, but then so is life.

In Object Oriented terms abstraction is the process of isolating those attributes of an entity which are important and ignoring those attributes which are not important.

An example might help.

Suppose you have a customer, and you wish to create a customer object. You don't actually create a customer object, but rather you create a customer class – the application then creates the object from the class. The customer class is the blueprint for all your customer objects. But, ultimately you want to end up with a customer object.

Let's define your customer. Her Name is Mary Smith. She is 38 years old, married with 3 children. She drives a 2 year old station wagon and lives in a quiet cul-de-sac. Her husband, Bob, is a plumber. Mary works part time as a dental nurse. She suffers from myopia, but wears contact lenses. Her mother is a keen golfer and her father plays bowls. etc, etc, etc.

Do you really want to know all about Mary just to sell her some widgets? I rather doubt it.

But you may be interested in her name and address, perhaps her phone number.

After Mary buys her widgets from you she goes down the street to keep an appointment with her optometrist. Now he does care about her myopia. That's just about all he does care about.

Next on her list of appointments is her doctor to get a new prescription filled for some sort of women's medication that I prefer to know nothing about. Her doctor knows about her 3 kids, and probably about her husband as well.

So here we have one person, and she is a customer of three different businesses. Each of them has an abstraction of Mary. Each of them capture different attributes of her because for each of them, different aspects of her life are relevant for the service that they provide for her.

But none of these abstractions is really Mary. They are just a representation of the essential bits, and what is essential for one person, may be irrelevant for another.