Using the Information Addressing Model of HyTime (ISO 10744) to Add Hypermedia Functionality to Legacy Data and Systems

Steven R. Newcomb, President
TechnoTeacher, Inc.

Adding Hypertext Functionality to Legacy Data

The HyTime standard allows any pieces of information to be addressed (and therefore to become the anchors of hyperlinks) in any convenient terms. These terms can be expressed in _any_ notation and they can be used to address _any_ information in _any_ notation.

In addition, HyTime provides more specialized mechanisms to meet frequently-encountered addressing needs, including:

addressing of information represented in SGML in terms of all of the inherent properties of information represented in SGML (e.g., hierarchy, attribute values, all other markup phenomena).
addressing of information represented in HyTime in terms of all of the inherent properties of information represented in HyTime (e.g., anchor status, position, extent).
addressing of information represented in any other (i.e., non-HyTime) SGML architecture in terms of all of the inherent properties of information represented in that architecture.
addressing of information that has, as one or more of its inherent properties, position in any arbitrary finite coordinate space.

The HyTime standard is designed to permit hyperlinks to exist in documents that are distinct and maintained separately from the documents containing their anchors. Therefore, and because of the extreme generality of HyTime's information addressing mechanisms, it is possible to use HyTime to express relationships (including traversible relationships) between any number of portions of any number of documents in any notations. Only the document(s) that contain the hyperlinks and their associated address location pointer information need be expressed using the HyTime standard.

Adding Hypertext Functionality to Legacy Systems

It is one thing to express a traversible relationship abstractly, as HyTime permits, but it is quite a different sort of challenge to support user-initiated traversal between anchors that are only viewable while running non-hypermedia legacy software. The technical obstacles to be overcome are as various as the systems themselves, not to mention their users and the requirements of those users.

Still, the structural and addressing abstractions that HyTime provides can be useful in several ways:

HyTime represents a great deal of careful object class design work that need not be re-invented for each retrofitting task. (HyTime's specification of the properties of aggregate locations is an example.)
HyTime provides a rigorous formalism for describing the properties of SGML-based information architectures (including, but not limited to, the HyTime architecture itself). These and other general facilities of HyTime can be especially useful in cases where there is no reason to cling to a legacy notation, and wholesale conversion is feasible, or where there is need to express formally, perhaps for the first time, the properties of a legacy notation for addressing purposes.
HyTime's abstractions can be supported by general-purpose software modules called "HyTime Engines." In some cases, these components can be useful in retrofitting existing software with HyTime awareness and functionality. When using such components, it is possible to approach the retrofitting problem in several ways:
- Change the legacy software so that it uses the HyTime engine's internal data structure.
- Change the HyTime engine so that it uses the legacy software's internal data structure.
- Change both the HyTime engine's internal data structure and the legacy software's internal data structure to some third data structure.
- Keep both the legacy software's internal data structure and the HyTime engine's internal data structure, and create software that performs bidirectional translation between the two structures.
- Some combination of the foregoing.

A HyTime Engine

One example of a HyTime Engine is the HyMinder(TM) system product of TechnoTeacher, Inc., a C++ library which offers an easy-to-use and comprehensive API to the information contained in SGML/HyTime documents. It is designed for those who wish to write applications that can create and/or process hypermedia documents represented in SGML/HyTime as well as for those who wish to create object-oriented SGML applications or retrofit existing applications for data interchange using SGML/HyTime documents.

The HyMinder system allows programmers to regard each syntactic and semantic construct described by the SGML and HyTime standards as a persistent C++ object; all such objects can be randomly accessed and manipulated while in database form, and/or automatically exported as SGML/HyTime. Using the HyMinder system, the structures, attribute values, contents, etc. of several databased SGML/HyTime documents can be simultaneously and rapidly read, written, and/or altered.

Limitations of the HyTime Approach

Support for real SGML is required. Many existing SGML systems do not offer support for the SGML standard that is sufficient to support the HyTime standard, often because their SGML entity management capabilities are too limited or do not conform.
The document in which a user session begins (the ``hub document'') must be a HyTime-conforming document. (However, no other documents in the linked set of documents [the ``hyperdocument''] need be expressed in HyTime or SGML.)
The hyperlinks and addresses must be expressed in a HyTime-conforming fashion. Otherwise, the linking and addressing information could not be universally understood.
Because it constitutes a large amount of predefined object-oriented design, there is a fair amount of lore and detail to be mastered by programmers, application designers, and information architects.

Three Examples of the Use of HyTime

Metafile for Interactive Documents (MID). A DoD document type definition for describing the behaviors of Interactive Electronic Technical Manuals (IETMs) and incorporating legacy and other data in them by query, by reference, and by inclusion. Information is available at ftp://navysgml.dt.navy.mil/pub/ietm/mid. HyTime linking and addressing modules are used in a working prototype.
Standard Music Description Language (SMDL). An ISO Draft International Standard (ISO/IEC DIS 10743) for describing music in terms of its abstract structure. Information is available at ftp://ftp.techno.com/HyTime/SMDL. HyTime scheduling, rendition, and linking modules are used. The European Commission is supporting the development of a prototype system for delivering legacy music information to sheet music outlets, etc. Information is available by request from S.R.Mounce@comp.brad.ac.uk.
Pinnacles Initiative. A consortium of semiconductor makers (Hitachi, Intel, National Semiconductor, Philips Semiconductors, and Texas Instruments) to allow them to provide product information (``Electronic Data Books'') to customers electronically in an interchangeable, system-neutral form. The Pinnacles DTD employs a minimal amount of HyTime syntax in order to support hyperlinks.

Reference Materials

Robin Cover's excellent and frequently-updated bibliography/database of materials regarding SGML and HyTime can by found at http://www.sil.org/sgml/sgml.html. If you have access to it, you do not need the list of references that follows.

DeRose, Steven J.; Durand, David G. Making Hypermedia Work: A User's Guide to HyTime. Boston/Dordrecht/London: Kluwer Academic Publishers, 1994. xxii + 384 pages. ISBN: 0-7923-9432-1.

Ferris, Ralph E.; Newcomb, Victoria Taussig (ed). HyTime Application Development Guide. Version 1.2. San Jose, CA and Rochester, NY: Fujitsu Open Systems Solutions and TechnoTeacher, Inc., May, 1995. 8 chapters, approximately 95 pages. Ralph Ferris is Project Manager, Electronic Publications, Fujitsu Open Systems Solutions, Inc., 3055 Orchard Drive, San Jose, CA, 95134-2022 (email: ralph@ossi.com OR ralphf@ix.netcom.com); Victoria Newcomb is with TechnoTeacher, Inc., P.O. Box 23795, Rochester, NY, 14692-3795. This document is available via anonymous FTP from ftp://ftp.techno.com/pub/HyTime/Application_Development_Guide

Goldfarb, Charles F. "Standards - HyTime: A Standard for Structured Hypermedia Interchange." IEEE Computer 24/8 (August 1991) 81-84. Author's affiliation: IBM Almaden Research Center, San Jose, CA, USA.

Goldfarb, Charles F. The SGML Handbook. Edited and with a foreword by Yuri Rubinsky. Oxford: Oxford University Press, 1990. 688 pages. ISBN: 0-19-853737-1. The authoritative reference on SGML, written by its inventor. Contains the entire SGML standard verbatim, with copious commentary.

International Organization for Standardization (ISO). ISO/IEC 10744:1992. Information Technology - Hypermedia/Time-based Structuring Language (HyTime). Edited by Charles F. Goldfarb (with assistance from Steven R. Newcomb). Geneva: International Organization for Standardization/International Electrotechnical Commission, 1992.

Kimber, W. Eliot. Practical Hypermedia: An Introduction to HyTime. Charles F. Goldfarb Series On Open Information Management. New York: Prentice-Hall Professional Technical Reference, [Spring/forthcoming] 1995. approximately 250 pages. ISBN: 0-13-309899-0. Author affiliation: Passage Systems, Inc. (W. Eliot Kimber (kimber@passage.com); Systems Analyst and HyTime Consultant; Passage Systems, Inc., 2608 Pinewood Terrace; Austin TX 78757 (512)339-1400; 465 Fairchild Dr., Suite 201; Mountain View, CA 94043 (415) 390-0911).

Newcomb, Steven R. "Multimedia Interchange Using SGML/HyTime. Part I: Structures." IEEE MultiMedia 2/2 (Summer 1995) 86-89 (with 2 references). ISSN: 1070-986X. Author's affiliation: TechnoTeacher, Inc.

Newcomb, Steven R. "Multimedia Interchange Using SGML/HyTime. Part II: Applications." IEEE MultiMedia 2/3 ([forthcoming] 1995) xxx-xxx. ISSN: 1070-986X. Author's affiliation: TechnoTeacher, Inc.

Newcomb, Steven R. "SGML Architectures: Implications and Opportunities for Industry." The SGML Newsletter 8/8 (August 1995) 1-5. ISSN: 1067-9197. Author's affiliation: TechnoTeacher, Inc. A version of this document is available via anonymous FTP from ftp://ftp.techno.com/pub/HyTime/conferences/ROCLING95/keynote.paper

Newcomb, Steven R. "Standards. Standard Music Description Language Complies with Hypermedia Standard." IEEE Computer 24/7 (July 1991) 76-79. ISSN: 0018-9162. Author's affiliation: Florida State University, Tallahassee, FL, USA; TechnoTeacher, Inc..

Newcomb, Steven R.; Kipp, Neill A.; Newcomb, Victoria T. "The 'HyTime' Hypermedia/Time-based Document Structuring Language." Communications of the Association for Computing Machinery 34/11 (November 1991) 67-83. ISSN: 0001-0782.

About the author:

Steven R. Newcomb is Vice Chairman of the American National Standards Institute's X3V1.8M Committee. Chaired by Charles F. Goldfarb, this committee was responsible for the seminal work on HyTime. Dr. Newcomb is President of TechnoTeacher, Inc., a software and consulting company in Rochester, New York. TechnoTeacher is the creator and vendor of the HyMinder(TM) object-oriented C++ libraries, which are used by SGML and HyTime application developers. Dr. Newcomb serves as Chairman of the Conventions for the Application of HyTime (CApH) Activity of the Graphic Communications Association Research Institute. He chairs the International HyTime Conferences held annually in Vancouver.

This paper appears in the Proceedings of the Second International Workshop on Incorporating Hypertext Functionality into Software Systems, held in conjunction with the ACM Hypertext '96 conference, Washington, U.S.A.

This document is located at

http://space.njit.edu:5080/HTFII/Newcomb.html