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Subject: Re: XML for data transmission
From: Joe Lapp <[log in to unmask]>
Reply-To:General discussion of Extensible Markup Language <[log in to unmask]>
Date:Thu, 2 Apr 1998 15:20:51 -0500
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At 02:38 PM 4/2/98 -0500, David Megginson wrote:
>El Melody Chile writes:
>
> > Quick question - data marked up using XML seems very verbose; does
> > this not mean it could be very inefficient as a means to exchange
> > data over networks?
>
>Text compresses nicely, especially when it's highly repetitive (like
>the same start and end tags over and over).

Efficiency has two sides: time and space.  XML takes time to parse and eats
a lot of space.  Compressing reduces space but increases parse time.  If
HTTP over TCP is to be the transport, then the transport becomes the
bottleneck, since both HTTP and TCP (connections) are slow by comparison
with other protocols.

I think the conclusion is that XML/HTTP/TCP is not suitable for distributed
real-time applications.  Even so, it remains desirable to minimize both
bandwidth and clock cycles.  HTTP and TCP are slow enough, let's not slow
them down any further; networks are already taxed for bandwidth, let's not
make the problem worse.  Hence, these issues are good things to think about.

The primary advantage of using XML as the message encoding is the
interoperability those messages have with other applications.  The messages
label all of their constituent data; the message becomes accessible to apps
even without hardcoding the app to receive that particular kind of message,
even when the message contains constituents that the app does not understand.

We use XML to wrap legacy applications (and new applications) so that
application services are invoked via XML documents (responses are also in
XML).  We don't care what the format of that XML document is.  We only care
that the data in the document is appropriately labelled, allowing us to map
between a variety of document formats and native services.

XML is verbose, and XML is slow.  Verbosity can be minimized at the expense
of speed, and speed can be minimized at the expense of interoperability.
So, I think the answer to the question is that XML is not well-suited to be
the message glue for all applications.  However, where the importance of
interoperability outweighs the other constraints, that's where XML belongs.

(P.S.  Why don't I ever seem to get copies of what I post to the list?  I
have no way of confirming that my posts actually make it to the list,
unless someone happens to respond.  Can anybody fix this?)
--
Joe Lapp, Technology Analyst | [log in to unmask]
webMethods, Inc.             | Voice: 703-267-1726
http://www.webMethods.com    |   Fax: 703-352-0370

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