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   Re: Streaming XML (Was RE: XML Information Set Requirements, W3C Note

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  • From: "Steven R. Newcomb" <srn@techno.com>
  • To: jborden@mediaone.net
  • Date: Wed, 24 Feb 1999 09:47:01 -0600

[Jonathan Borden:]

> Interesting. Is the DOM just an API, or a set of
> interfaces which define a hierarchy of objects?
> That is, an IDL interface definition is a type
> of formal definition. For example, using
> Microsoft's COM, IDL compiles into a
> 'typelibrary' which is a binary representation
> of something analogous on some level to a
> property set. A scripting language, to continue
> the example, can employ any object with a
> typelibrary and associated interface set.

> Would it be possible to generate IDL
> programmatically from a property set definition?

Even though I'm not well versed in IDL, I feel
certain the answer is "Yes".  Rigorous
machine-readable expressions of information
models, such as property sets, are extremely
useful things.

> If so, then aren't the two alternate
> representations of the same information?

No, not really.  An interface specification is
about a particular way of accessing information.
Starting with an IDL specification, one could make
inferences about the nature of the information
being accessed, but that's about all.  The
difference between an API and an information model
is subtle, but they are really very different
things.  One way to think of the difference is

* an information model is about what *is*, while

* an API is about what one *does*.

This same difference goes to the very heart of
what makes XML great.  XML is emblematic of
industry's ongoing historic shift of focus away
from processing, and toward the information that
is being processed.

> > There is every reason to believe that the XML
> > Information Set, once Recommended, will be
> > expressible as a property set.  Once this is done,
> > XML objects will be processable, addressable, and
> > re-usable via the same software that supports the
> > processing, addressing, and re-use of components
> > of resources expressed in other notations, with
> > each such notation described by its own property
> > set.  In that scenario, all information components
> > conform to the same object model, the ISO "grove"
> > object model, so we are able to address (link,
> > re-use) any kind of thing.

> 	This is the same language used to describe
> the virtues of COM. Not to denegrate the virtues
> of property sets, but why are property sets
> specifications, and IDL definitions an API?

(It doesn't matter to me whether we call property
sets or APIs "definitions" or "specifications".)

Property sets are about what underlies APIs.  An
IDL definition is a particular way to get at some
information.  Another kind of API definition would
do equally well for the same information set.
Property sets are about what both such APIs would
have in common.  Property sets are more abstract
than APIs.

(COM is about a particular software vendor's
attempts to retain its position of having its
proprietary software products be indispensable to
users.  COM's intent is 180 degrees removed from
the intent of property sets.  The intent of
property sets is to protect the interests of
information owners and users, and to re-focus the
attention of software vendors on the interests of
such information owners and users, instead of on
finding creative ways to lock the customer into
particular software product lines.)


Steven R. Newcomb, President, TechnoTeacher, Inc.
srn@techno.com  http://www.techno.com  ftp.techno.com

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