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RE: Internal subset equivalent in new schema proposals?

• From: Ronald Bourret <rbourret@i...>
• To: "xml-dev@i..." <xml-dev@i...>
• Date: Mon, 23 Nov 1998 10:01:17 +0100

Don Park wrote:

> Interesting question.  I just found out that XSchema does allow inline
> XSchema elements (5.1.2) but I am not sure if it supports schema
> inheritance.
>
> Actually, my questions were more or less regarding existing support. 
 DCD,
> XML-Data, and RDF does not seem to support inline schema although they do
> allow declaration of datatypes in data instances.
>
> I think inline schema is particularly important in applications like 
digital
> television and smart cable boxes where content variation is tremendous. 
 It
> is possible to do this through multiplexing/tunneling but it would be 
nice
> to have a single stream of XML data which can handle open variety of
> contents (drama, shows, program schedule, advertisement, closed captions,
> etc.)

Neither DCD nor SOX define how a schema is associated with an instance 
file, so it's hard to say whether they have this capability.

XSchema uses a PI to associate a schema with an instance file and allows 
multiple PIs to be used.  The effect is cumulative, as if the schemas from 
all the referenced files were in a single file.  Thus, an instance could 
include a custom schema in addition to the standard schema.

However:

1) This isn't really the same as the relation between the internal and 
external subsets.  In particular, it is not possible to override/add 
attributes (these are inside element declarations and the duplicate element 
declaration needed to contain the new attribute would cause an error), nor 
is it possible to override/add parsed entities because XSchema does not 
support parsed entities.

2) XSchema PIs that occur after the root element are ignored, so this 
doesn't help in your case.

Note also the inline XSchema elements (which we included based on your 
suggestion of last August) are considered experimental and subject to 
change.

-- Ron Bourret


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