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- From: David Megginson <firstname.lastname@example.org>
- To: XML-Dev Mailing list <email@example.com>
- Date: Wed, 24 Feb 1999 16:34:16 -0500 (EST)
Tom Harding writes:
> David Megginson wrote:
> > 1. Use a non-XML mechanism for separating XML packets -- that
> > way, there's not a tight dependency between the stream-handler
> > and the parser (the stream handler knows the bounds of each
> > packet without doing any XML parsing).
> What bit sequence would you use as a separator and how would you
> ensure that no conceivable encoding would produce it spuriously?
I'm talking about characters, not bit sequences. For a simple
solution, you should provide the entire stream in the same character
encoding (remember that a transport protocol is allowed to override
the encoding in the XML declaration or encoding declaration).
Otherwise, the packets will need to be escaped somehow.
> > 2. Separate information about the packages from the packets
> > themselves. The information could be linear, or it could
> > itself be XML packets of a different sort. You should not
> > have to parse an entire packet to know its sequencing, etc.
> How could you terminate a document with another doc element? The
> only thing allowed after all legitimate Misc markup at the end of a
> document is more Misc markup.
But you're not performing XML parsing at all until you take the stream
apart first -- in other words, all the XML parser sees is the part
between the separator characters. This is the kind of layered
approach that makes for simple, maintainable systems.
> > Putting a PI in the XML packet itself seems a little awkward to me.
> How about thinking of it as a "network-ready" document? Or if you
> like, explicitly define a "packet" as such a document.
No, it still looks like a messy architecture to me, because the
transport layer has to know about the packets -- it has to parse the
XML about to get information about what it's looking at, and that adds
complexity and inefficiency. A clean architecture should separate the
layers completely, and use XML only where it has an obvious advantage
over other approaches.
All the best,
David Megginson firstname.lastname@example.org
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