Re: 2 Questions. Any Answers?

On Tue, Jul 14 1998 Tim Kennedy - WebPhD wrote:

> #1. Who could explain me the relationship between the SMIL technology and
> Hypermedia/Time Based Structuring Language (HyTime, ISO 10744)? Is HyTime
> location addressing available for SMIL? Are there any architectural issues
> concerning SMIL?

THE SHORT ANSWER (with pointers to very long answers)

We at CWI have designed an environment, called Berlage, that uses
DSSSL to transform storage documents defined with HyTime into final
hypermedia presentations defined with SMIL.  We have published a paper
describing this environment at Digital Libraries 98.  This paper, "The
Use of Existing Public Domain Standards and Tools for Adaptive
Hypermedia", can be accessed at URL

  http://www.cwi.nl/~lloyd/Papers/DL98/dl98.ps

Related papers that we'll be publishing in upcoming conference
proceedings are "Structural Distinctions between Hypermedia Storage
and Presentation" at ACM Multimedia 98 in Bristol, UK in mid-September
and "Implementing Adaptability in the Standard Reference Model" at
Multimedia Modeling 98 in Lausanne, Switzerland in mid-October.  I
will also be presenting tutorials on this cooperative use of HyTime,
DSSSL and SMIL at ACM Multimedia 98 and at MetaStructures 98 in
Montreal, Canada on August 17th.  (At MetaStructures 98 I'll also
be presenting a tutorial on SMIL itself).

THE LONG ANSWER

The SMIL specification says nothing about HyTime; there is no formal
direct relationship between the two standards.  However, there are
several indirect relationships.

The indirect relationships between the two languages are based on the
fact that both are SGML subsets, defined as such in different ways.
XML is an SGML subset whose syntax defined with an SGML declaration.
SMIL's syntax is defined with an XML Document Type Definition (DTD).
XML DTDs are subsets of SGML DTDs.  Thus SMIL documents can be
processed as SGML with the DTD and the XML declaration.  HyTime is an
SGML subset whose syntax is defined with an SGML architecture.
Documents conforming to many different DTDs can be HyTime documents.
XML documents can also be HyTime documents.  For a document to be both
XML and HyTime, it would have to stick to the subset of SGML
constructs defined by XML's SGML declaration, and it would have the
attributes used by its elements fit the restricts established by
HyTime's SGML architecture.  The attributes in SMIL documents that
have semantics appropriate for HyTime processing generally cannot be
processed as conforming to HyTime.

The W3C efforts XLink and XPointer define attributes with particular
linking semantics that can be put in XML documents and DTDs.  The
semantics of XLink are based on the semantics used in HyTime linking.
The semantics of XPointer are based on the semantics used in HyTime
location addressing.  There are similarities between XLink and
XPointer syntax and HyTime syntax.  Upcoming versions of SMIL may
incorporate XLink and XPointer after they are finished.  However,
there is no effort to make XLink and XPointer HyTime compliant, so
such future versions of SMIL will still not be HyTime compliant.

An important distinction to bear in mind between SMIL and HyTime is
that SMIL encodes a single adaptive presentation whereas HyTime,
generally speaking, encodes a presentation-independent archival
structure around stored media objects.  This view of HyTime matches
the original intent of SGML as a storage structure which can be
transformed to many different styles of typeset format or other types
of final presentation.  HTML is an example of an SGML DTD-defined
document set that does directly define final presentation, as is SMIL.
But the general intent of SGML, and of HyTime, is storage-level
representation.

DSSSL is the ISO standard for specifying the transformation of SGML
and HyTime documents to final presentation.  A DSSSL program, or
"style sheet", can take an SGML/HyTime document (usually one style
sheet applies to any document of a given DTD) and output, among other
formats, another SGML document.  This SGML output can conform to a
presentation-oriented DTD, such as HTML or SMIL.  Many existing Web
sites use DSSSL to generate HTML from a source SGML document set.
SMIL can get generated from SGML and HyTime using DSSSL in the same
manner.

-Lloyd

--
Lloyd Rutledge                                         vox: +31 20 592 41 27
CWI (Centrum voor Wiskunde en Informatica)             fax: +31 20 592 41 99
Kruislaan 413,  NL-1098 SJ Amsterdam, The Netherlands  net: lloyd@cwi.nl
P.O. Box 94079, NL-1090 GB Amsterdam, The Netherlands  http://www.cwi.nl/~lloyd

Received on Wednesday, 15 July 1998 04:02:03 UTC