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HyTime (ISO 10744:1992) is a standard that describes a framework based
on SGML (ISO 8879:1986) for the encoding of documents that may include
activities that occupy multiple dimensions (such as time and space),
that include multiple types of content (not all of which need be
represented in SGML). HyTime documents may be created either for
interchange or local processing. The "hub document" that is at the
center of a HyTime document must be in SGML. HyTime envisions more uses
of documents than simple display (for which reason it includes such
things as a query language and a language for lexical processing of SGML
attributes). HyTime was developed by ISO/IEC JTC1/SC18/WG8, which also
developed SGML and is completing work on DSSSL (Document Style Semantics
and Specification Language, ISO DIS 10179), another SGML processing
standard that is complementary to HyTime in may ways.

MHEG  (Multimedia/Hypermedia Experts Group) is the old name of a group
that is now included in ISO/IEC JTC1/SC29. Their charter is somewhat
different from that of the group that developed HyTime. Their proposed
standards will concentrate on data structures for objects that are
directly interpreted. (Their background is in JTC1/SC2, the committee
responsible for coding standards like the international counterpart of
ASCII, ISO 646). The MHEG standard will most likely include a new
repertoire of control functions (i.e., the hypermedia functional
extensions of such things as CR, LF, TAB, BEL) that can be the
initiations of direct action on terminals of limited intelligence. Their
interests seem to be in providing new kinds of services for common
carriers (e.g., AT&T, British Telecom) that go beyond current services
like teletext. 

There is some common membership between the two communities of standards
developers and official liaison about their projects. WG8's liaison to
MHEG is:

Brian Markey
	Siemens Nixdorf Information Systems, Inc.
	Research and Development Division
	4 Cambridge Center
	Cambridge, MA 02142

	tel:	(617) 349 5045	(direct line, rings at my desk)
		(617) 864-0066 X 1045 (main switchboard)
	fax:	(617) 864-3176
	email:	bmarkey@sni-usa.com

Mr. Markey may be able to clarify further the relationship between
HyTime (to which he was a major contributor) and the work of MHEG.


James D. Mason
Convenor, ISO/IEC JTC1/SC18/WG8
masonjd@ornl.gov