Re: The Meaning of Abstract
From: David B. Held (dheld_at_codelogicconsulting.com)
Date: 06/02/04
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Date: Tue, 1 Jun 2004 17:38:57 -0500
"Eray Ozkural exa" <erayo@bilkent.edu.tr> wrote in message
news:fa69ae35.0406010857.4d6ce246@posting.google.com...
>
> I'm surprised that some people take "abstract" as a vague
> common-sense concept. To me, it has a precise technical
> meaning: lossy compression.
I have to agree with Mr. Hughes. If you find that to be the
essential feature of "abstraction", then I fear you haven't
abstracted the notion properly. ;) I think a better meaning is:
to identify the necessary features of a concept. "Lossy
compression" is insufficient to describe this version because
it often includes features that are *not* essential to the
abstraction of an instance. If I show you a picture of a girl,
and you produce a JPEG image of it and present it to me as
"an abstraction", I'll say you're full of it. Now, if I ask a 5 year
old to draw what he sees in the picture, he will most likely
draw a stick figure of a girl, identifying what he believes to be
the essential features of the image. And I'm fairly certain that
a large survey with our two "abstractions" will show that the
stick figure is a much better abstraction than the JPEG. Why?
Because the JPEG contains too much information. It takes
out redundant information, but only on a local level. The JPEG
compression algorithm necessarily cannot identify the information
contained in the picture that depends on having human knowledge
and experience. And that is why it does not produce a useful
abstraction. The same can be said of the MP3 file. An MP3 is
not a very good abstraction of the original. But a piano rendition
with a monophonic melody and simple chord accompaniment
*would* be what many musicians regard as an "abstraction" of
the original song.
> A program is abstract, because it *loses* the architectural details
> of a computation, and it is concise.
Actually, programs aren't very abstract at all. They tend to be rather
concrete engineering solutions to practical problems. And a review
of www.dictionary.com shows that "concrete" and "practical" are
practically antonyms of "abstract".
> A blueprint of a house is abstract because it *loses* the
> architectural and material properties of an actual house, and it is
> concise.
> [...]
A blueprint is certainly more abstract than an actual house, but not
because of what it is missing. It is abstraction because of what it
has, which is the essential features of the house. Whether it
specifies the placement of all the electrical outlets or not is of no
concern. Whether it conveys the proper layout of rooms and floors
is. If I created a blueprint that located all the electrical outlets in the
house but not any of the walls, according to your definition, it is an
"abstraction" of the house, because I have *lost* detail, and created
a "concise" version of the house. But merely losing detail is not the
key feature. The key feature is identifying the details that we use to
classify the concrete instances. Abstraction is a notion concerned
with classes and types, not details and data representation. Such
a definition is not sufficiently "abstract".
Dave
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