- From: Lloyd Rutledge <Lloyd.Rutledge@cwi.nl>
- Date: Wed, 15 Jul 1998 10:02:16 +0200
- To: www-smil@w3.org
- cc: Lloyd.Rutledge@cwi.nl, Tim Kennedy - WebPhD <Tim@WebPhD.com>
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