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
Contents i
Foreword xi
Conventions xv
Acknowledgments xvii
PART I
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
PART II
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
PART III
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
APPENDIXES
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
FOREWORD
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
extends.
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
University.
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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