xml-dev - Re: Notations

["Rick Jelliffe" <ricko@allette.com.au>]

From: Ronald Bourret <rbourret@ito.tu-darmstadt.de>


>Dean Roddey wrote:
>> Just from a practical standpoint though, if you found an element that
had
>> say three notations. One said it was MIDI, one said it was Base64,
and
>one
>> said it was zipped. Was it base64'd then zipped, or zipped then base
>64'd?
>> How would one indicate the ordering of original transformations in
such a
>> situation, so that it could be untransformed correctly back?
>
>Your application would need to know the order.  Given that there are no
>standard notations at the moment, this doesn't seem unreasonable, as
the
>application needs to know what the notations mean, anyway.

There are plenty of standard notations. My book has about 150 of them,
for example: including date and regular expressions. But the (ISO)
standard notations tend to be for file-level data rather than for
field-level data. Personally, I don't expect vendor-based consortia to
standardize notations very much: I think that SGML and HTML experience
shows that they will try to use XML as a vehicle for competing by adding
in-house notations, customized for their products.

As far as sequence goes, there is an ISO standard method "Formal System
Identifiers" (FSIs). If people want them, they can be retrofitted on top
of URLs. They basically embed a pseudo-start tag into the SYSTEM
identifier of an entity declaration, and give unpacking information for
the storage system.  They can be cascaded (or, at least, pipelined) to
allow you to request, for example, a file called "x" which is gzip
compressed in a tar achive called "y" which is sitting as the third file
in an multipart MIME email, which has been hex-encoded and which has a
checksum.

I think FSIs would be a good idea in XML. They fit in between URIs and
XPointers, I suppose. I don't think URIs can provide pipelines and I
don't think XPointers can provide extended functions like checksums.
However, URIs and XPointers do a lot, and they may do enough.

Rick Jelliffe



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