Making Hypermedia Work - Table of Contents and Foreword

Making Hypermedia Work: A User's Guide to HyTime
by Steve J. DeRose and David G. Durand


Contents  i
Foreword  xi
Conventions    xv
Acknowledgments     xvii
1  Introduction     3
1.1 Purpose and scope of this book 6
1.2 What is HyTime for?  8
1.3 What can HyTime do?  9
1.4 How to use this book 10
2  Hypermedia Concepts   13
2.1 Introduction    13
2.2 Print examples of hyperdocuments    14
2.3 Documents and links  21
2.4 Open systems    27
3  Overview of SGML 35
3.1 What is SGML, really?     35
3.2 Parts of an SGML document 39
3.3 SGML basics     40
3.4 A sample SGML document    51
3.5 Optional SGML features    58
3.6 Formal public identifiers 61
4  HyTime Quick Start    65
4.1 Clink, the basic point-to-point link     65
4.2 Linking to destinations without IDs 67
4.3 HyTime locators 68
4.4 Graphic locations and geometry 70
4.5 Linking by searching 71
4.6 More complex link structures   72
4.7 HyTime and SGML element types  74
5  The Structure of HyTime    77
5.1 Basic HyTime concepts     77
5.2 Architectural forms  79
5.3 SGML issues in HyTime     90
5.4 HyTime's hyperdocument model   92
5.5 How a HyTime system fits together   94
5.6 HyTime declarations  97
5.7 The HyTime modules   99
6  Basic Measurement     103
6.1 Introduction to measurement    103
6.2 Geometric concepts   104
6.3 Architectural forms  105
7  Hyperlinks  109
7.1 Introduction    109
7.2 Basic Concepts  109
7.3 Architectural forms  114
7.4 Hyperlinks and webs  118
8  Locating Data Objects 121
8.1 Introduction    121
8.2 Naming, counting and querying  121
8.3 Named location addresses  123
8.4 Coordinate location addresses  131
8.5 Semantic locations   145
8.6 Creating robust pointers  151
8.7 Aggregates and spans 153
9  The HyTime Query Language  159
9.1 Purpose and basic capabilities 159
9.2 An example 160
9.3 HyQ syntax 162
9.4 The HyQ functions    163
9.5 HyQ and other query languages  186
10  Modifying a DTD for HyTime     189
10.1 Introduction   189
10.2 HTML and the World Wide Web   190
10.3 The DTD conversion  195
10.4 Evaluating a HyTime product   202
10.5 Summary   203
11  Lexical Types and Properties   207
11.1 Introduction   207
11.2 Introduction to lexical types 208
11.3 HyTime lextype type constraints    210
11.4 Defining lexical models  210
11.5 HyLex     213
11.6 Accessing public lexical types     220
11.7 HyTime properties   222
11.8 Property definition 227
11.9 Inherent property definitions 230
12  Extending HyTime     237
12.1 Introduction   237
12.2 HyQ extensions 238
12.3 Lexical types  240
12.4 Properties     241
12.5 Specific elements for media links  241
12.6 A protocol for hot spots on graphs 246
12.7 TEI  248
13  Advanced Measurement and Scheduling 253
13.1 Introduction   253
13.2 Units of measurement     254
13.3 Axes and finite coordinate spaces  257
13.4 Events and extents  260
13.5 Representing tables 267
13.6 Marker functions    271
13.7 Other features 273
14  The HyTime Base Module    275
14.1 Introduction   275
14.2 Entity trees   276
14.3 Base module option summaries  276
14.4 The all-id attribute form     280
14.5 The all-lex attribute form    284
14.6 The lexmodel architectural form    285
14.7 The lexord architectural form 285
14.8 The all-ref attribute form    287
14.9 The all-act    292
14.10 The any-dcn   293
14.11 The all-qual  294
Appendix A  HyTime Meta-DTD   295
A.1 Base module (clause 6)    296
A.2 Measurement (clause 7)    301
A.3 Location address (clause 8)    305
A.4 Hyperlinks (clause 9)     309
A.5 Scheduling (clause 10)    310
A.6 Rendition (clause 11)
A.7 Useful types and notations     317
Measurement (annex A.5)  318
Appendix B  Graphics Notations     321
Appendix C  HyTime Reference Material   327
Bibliography   333
Glossary  341
Index     359


HyTime is the first official standard for describing the structure
of time-based hypermedia documents. Its marketplace acceptance is
yet to come. This book, presenting the first in-depth guide to the
HyTime specification, both describes its key features and provides
guidelines on how it is used. It has been written by two leading
experts in the field who have had significant impact on its
development and are experts in SGML, the prior standard that HyTime

HyTime represents a confluence of two technical fields and the
socio-politico-economic standards process. The two technical
fields, hypertext/hypermedia and document processing based on
declarative markup, have been maturing over the last three decades.
The first researcher to build a hypertext system, Doug Engelbart,
in the late '50's articulated his vision for computer systems that
would augment human intellect and in the mid-'60's built NLS (the
oNLine System) to realize that vision; this monumental system
pioneered, among other features, outline editing, journaling,
significant linking facilities, and mouse-based interaction with
text and graphics on raster displays. In 1967 Theodor Nelson,
coiner of the word hypertext, co-designed with me and my students
the Hypertext Editing System, the first hypertext system to run on
commercial computer and display equipment. These early hypertext
systems allowed users not just to create and follow links, but also
to do interactive editing and word processing far more
sophisticated than was available via the line editors of the day,
as well as to specify formatting codes for subsequent batch
processing and printout. Linear document production, however, was
a byproduct, not the main purpose of these interactive authoring
and browsing systems. The second, much larger community worked on
document production with increasingly sophisticated batch
formatters. Here the leap forward was to replace procedural format
codes and macros with declarative markup codes that separated the
identification ("tagging") of document elements from their
formatting, generalizing the commonly used format macros. In the
70's this idea was the focus of Charles Goldfarb's GML built at IBM
and of Brian Reid's Ph.D. dissertation on Scribe at Carnegie-Mellon

While rich in functionality, both hypertext/hypermedia systems and
document-production systems have been developed as closed,
one-of-a-kind systems that force users to live on technology
islands. Ted Nelson realized hypertext technology could make
possible a universal, integrated super library or "docuverse;"
however because of the lack of interoperability of today's closed
systems, we have only "docuchaos."  Standards, painful as they are
to produce and implement and imperfect as they are by virtue of the
politically charged process of compromise, at least have the virtue
of being designed for interoperability. As one who has worked over
several decades on 3D graphics standards, I am really pleased to
see SGML taking off; already entire industry segments such as
aerospace, telecommunications, and pharmaceuticals have agreed on
DTDs (Document Type Definitions) that embody codes of practice for
documentation in their industry, so that documents can be easily
transmitted and exchanged, regardless of the systems used to author
and present them. The firm hand of the DOD has certainly played
a useful role here, through the CALS initiative. On the other side
of the spectrum, humanists, in the Text Encoding Initiative, have
labored to produce a comprehensive DTD for data interchange in
literary research.  And most encouraging, vendors of
word-processing software such as WordPerfect have announced support
for SGML and are providing both import to and export from their
proprietary formats. The key reason to prefer SGML as the exchange
format over industry standards such as PostScript and RTF is that
the latter describe merely formatting, not structures that can be
presented on display media in a variety of ways; SGML is more
powerful because it retains the vital information that describes 
the document not as a collection of typeset pages but as hierarchy
of multi-media elements.

But the designers of the HyTime standard foresaw that SGML would
not be powerful enough to deal with time-based multi/hypermedia
"documents," since it lacked support for many aspects of rich
hypertext and time-based media. HyTime's hypertext features are
sufficiently complete to provide a superset of the features in many
hypermedia publishing systems available today, including, for
example, Brown's Intermedia system and the World Wide Web.
It handles multimedia by providing detailed means for specifying
coordinate systems and ranges, without specifying the
representation, storage and presentation of the media themselves.
It has features for scheduling and synchronizing these media as
well, though they will probably not be available in the first
HyTime engines. Thus HyTime will probably first be used primarily
to encode hyperdocuments with text, sound, and 2D graphics and
images. I hope that HyTime will open new areas of capability in
synergy with industry proto-standards such as Apple's QuickTime
that address related concerns.

Steve DeRose and Dave Durand are uniquely qualified to write the
definitive book on HyTime. They are among the few with extensive
experience in both hypermedia (since the late '70's) and in SGML
(since the mid-'80's); a combination of expertise in both these
areas still remarkably rare. Steve and Dave have published papers
on SGML and mark-up theory. Steve is the chief architect of
Electronic Book Technologies' DynaText system, the first
commercially available SGML-based hypermedia publishing system, and
wrote the SGML parser for that system. Both have been leaders in
designing and documenting the hypertext part of the guidelines for
the Text Encoding Initiative, as well as providing technical SGML
advice to the project. Most importantly, at the first Hypertext
Workshop in 1987 they advanced the first proposal for an SGML-based
hypermedia system, and went on to influence the HyTime standard.
Steve, for example, was a principal architect for HyQ, the query
language of HyTime. Thus they write from deep experience and
authority on HyTime, and have created a work that will be a key
ingredient in the complex process of putting a standard into
successful practice.

     Andy van Dam
     Providence, RI
     January, 1994

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