Re: W3C draft "Synchronized Multimedia Integration Language"

> Can someone explain to me the relationship between this proposal and HyTime?
> 
> Thanks,
> 
> Dan

The simple answer is: there is none.  The specification of SMIL is
done with no mention of HyTime whatsoever.  No HyTime code or
processing of HyTime code is at all required to encode, author, or
process SMIL code.  Anyone who uses SMIL can pretend HyTime does not
exist.

The more complicated answer (and one that only XML/SGML/HyTime geeks
will care to read) is that SMIL's use of XML provides some
relationships between SMIL and HyTime.  All SMIL documents are encoded
with XML and processable as such.  XML can be considered a
"meta-language".  An XML DTD (Document Type Declaration) is used to
define the SMIL format.  This enables an SMIL document to be processed
with the XML DTD by and XML parser to validate that the document does
(or does not) conform to SMIL.  The XML DTD for SMIL also attaches
some XML-defined semantics to certain SMIL elements and attributes.
This means that when processed by XML systems these semantics will be
detected even if the XML system knows nothing of SMIL.  (Of course
these XML semantics are not sufficient to fully describe SMIL
semantics, but they provide a common foundation).

The resulting tie-ins with HyTime are

1) XML is a "subset/simplification/extension" of SGML, which is a used
to define HyTime.  Any XML document can be processed as SGML.  Thus,
any SMIL document can be incorporated into a HyTime
document/environment using HyTime declarative constructs and
processing.

2) SMIL is defined as a DTD.  A HyTime "overriding" DTD could
potentially be written that expresses some of the HyTime-encodable
hypermedia semantics within SMIL as HyTime-recognized constructs.
These HyTime constructs would be recognized by HyTime systems.
However, there are limitations to this approach.  (See
ftp://devo.cs.uml.edu/pub/hytime/IASTED_95.ps.gz for a paper
discussing this approach as applied to HTML).

3) The XML semantics attached to SMIL by the DTD are based on HyTime.
This is especially to for XLL (Extensible Linking Language) within
XML.  HyTime is not used to defined these constructs, but they
correspond very closely with HyTime (and were developed by several of
the same people who developed HyTime).

4) The XML proposal for XML "namespaces" is based on the HyTime
specification of architectures.

These tie-ins have several ramifications for potential applications of
HyTime to SMIL.  None of these, to my knowledge, have been explored or
proposed.

Lloyd

Received on Monday, 8 December 1997 06:45:17 UTC