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- From: Clark Evans <firstname.lastname@example.org>
- To: XML Dev <email@example.com>
- Date: Wed, 03 Feb 1999 21:21:26 +0000
Perhaps the role of namespaces is fundamentally
different in the "stream processing" paradigm
than it is in "object processing" paradigm?
Could this be the issue underlying the current
debate? I don't know enough on the topic to
say. However, I feel I can help by explaining
my observations about the differences between
1. A tenant of object oriented programming
is encapsulation, data hiding. For stream
processing it is the opposite, data exposure.
2. Objects are modified or undergo state change
by invoking methods. Where streams are re-written
or translated by transformations.
3. Ideally, an object retains it's identity.
The entire goal of a stream is to merge it's
information with each and every observer; this
is equivalent to identity loss.
4. An object has a 1-1 correspondence between its
data and its code. A stream has a 1-M correspondence
between its data and its code. Where the document is
the data, and the code is the observer's
5. Objects are finite, they have a boundry.
Streams may be effectively infinite. For
example, a pressure transducer sending water
level measurements may operate continuously
for years! Thus, you can store an entire
object in memory, you may not want to store
an entire stream in memory.
6. An object's interface describes a block of
functionality provided. A stream's interface
describes the information conthat it carries.
7. An object has one type or class which is
assigned to the data, where a stream can
be classified differently by each and every
observer. This is especially clear if
you read about Arcetectures.
Anyway, I'm not saying that one is better
than the other, just that they are different
and subtly interwoven. For instance, Scenerios
is the study of object interactions as
a stream of events. And SAX is a wonderful
event-driven stream observer object.
I feel that the key to the success of XML
is to recognize that it is part of a different
paradigm --XML complements existing technology.
As such, it is important to scrutinize the
application of object-oriented idioms to the
Hope this helps,
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