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\def\HT{Hyper\-\TeX}
\def\XHDVI{\emph{Xhdvi}}
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\Large
\bfseries The \HT\ project\\[6pt]
\itshape Arthur Smith\\
\large \upshape\mdseries (edited by Sebastian Rahtz)
\end{center}

\subsection*{Introduction}

The past year has seen a revolution in the processes of
Internet-based information navigation and retrieval with the
advent of easy-to-use graphical browsers (in particular Mosaic)
based on the World-Wide-Web (WWW). The revolution is a result of two
components. First, the browsers allow a near-uniform (point-and-click
or other method) access to documents in almost any format
and from almost any Internet-based
source; along with this the Universal
Resource Locator (URL) mechanism provides
a surprisingly easy and uniform way to specify the location of any
document on the net. Second, for certain classes of documents
(html files, or gopher text files) embedded URL's or other
addresses are understood to refer to other, external, documents which can
be followed according to the interests of the person viewing the
document, producing an interconnected web of documents.

The goal of the \HT{} collaboration is to extend this second
privileged class of documents to include documents based on \TeX{},
the word-processing language of choice for mathematical and scientific
writing, thus fully incorporating \TeX{} documents into the burgeoning
\textbf{web} of information on the internet.  The \HT{} introductory
document is at \URL|http://xxx.lanl.gov/hypertex/|.

\subsection*{How does it work?}

The underlying element of our implementation of \HT{} is the use
of a \TeX{} macro that bypasses the \TeX{} interpretation process and
sends a message directly to the \emph{dvi} interpreter that processes \TeX{}
output, via the +\special+ command. The original \HT{} specification (due
to Paul Ginsparg, Tanmoy Bhattacharya, and me) uses the initial
characters \emph{html:} to denote \HT{} elements in an HTML-like
style. After the initial \emph{html:} string, the specification is identical
to a restricted form of HTML. The five arguments we have added to
the command are:

\begin{description}
\item[href:] +html:&lt;a href = "href_string"&gt;+
\item[name:] +html:&lt;a name = "name_string"&gt;+
\item[end:] +html:&lt;/a&gt;+
\item[image:] +html:&lt;img src = "href_string"&gt;+
\item[base\_name:] +html:&lt;base href = "href_string"&gt;+
\end{description}

The \emph{href}, \emph{name} and \emph{end} commands are used to do
the basic hypertext operations of establishing links between sections
of documents. The \emph{image} command is intended (as with current
html viewers) to eventually place an image of arbitrary graphical
format on the page in the current location. Currently for \XHDVI,
\emph{image} brings up an external viewer with the image, if such
a viewer is available. The \emph{base\_name}
command should be used to communicate
to the \emph{dvi} viewer the full (URL) location of the current document so that
files specified by relative URL's may be retrieved correctly.

The href and name commands must be paired with an end command later in
the \TeX{} file --- the \TeX{} commands between the two ends of a pair
form an \emph{anchor} in the document. In the case of an +\href+
command, the \emph{anchor} is to be highlighted in the \emph{dvi} viewer, and
when clicked on will cause the scene to shift to the destination
specified by \emph{href\_string}. The \emph{anchor} associated with a
name command represents a possible location to which other hypertext
links may refer, either as local references (of the form
\texttt{href="\#name\_string"} with the \emph{name\_string}
identical to the one in the name command) or as part of a URL (of the
form \emph{URL\#name\_string}). Here \emph{href\_string} is a valid
URL or local identifier, while name\_string could be any string at
all: the only caveat is that `+"+' characters should be escaped with a
backslash (+\+), and if it looks like a URL name it may cause
problems.

Because this html-based naming scheme is somewhat unwieldy, although
very general, Tanmoy Bhattacharya (\Email|tanmoy@qcd.lanl.gov|) has
written several collections of \TeX{} macros to simplify things.  The
packages are in \URL|http://nqcd.lanl.gov/people/tanmoy/hypertex/|. An
alternative \LaTeXe\ package is |hyperref|, by Sebastian Rahtz and
Yannis Haralambous, which is available on CTAN as
\path|macros/latex/contrib/supported/hyperref|. This has additional
functionality for conversion to PDF.

\subsection*{How do I use it?}

There are currently three \emph{dvi} interpreters that understand the
\HT{} +\special+s: \XHDVI{} for X windows, HyperTeXView.app for
NextStep, and +dvihps+, a version of +dvips+ that understands \HT{}
and puts +pdfmark+ commands in the output for Adobe's Distiller to
process.  For a \TeX{} document that has already been processed to a
\emph{dvi} file with \HT{} elements, viewing the internal hypertext is
almost trivial --- you just fire up the \emph{dvi} previewer and
navigate by button clicks.

The software available is:

1. A \HT{} viewer based on xdvi-18, modified by Arthur Smith.  
\URL|ftp://snorri.chem.washington.edu/hypertex/xhdvi_0.6.tar.Z| 

2. HyperTeXview.app,
  courtesy of Dmitri Linde (also the author of InstantTeX.app) for
  NextStep, precompiled for Motorola and Intel-based NeXT
  machines. See \verb|http://xxx.lanl.gov/hypertex/index.html#dvi|
  for  availability.

3. \emph{dvihps}, from Mark Doyle, converts the \HT{} commands to a form
which can be processed by Acrobat Distiller. See the \HT{} WEB
home page for location. Other PostScript interpreters are free to
pick up the \emph{pdfm} operators as well. For instance, Tanmoy has
hacked Ghostview to pick up the links and make them active.  This
can be found at
\URL|http://nqcd.lanl.gov/people/tanmoy/hypertex/ghostview-1.5-hacked.tar.gz|.

Here is where the power of \TeX's macro capabilities appears.
A working internal hypertext document can be made from a \LaTeX\ 
document with a one-line addition to the file, using one of the
hypertex macro packages. These convert the standard \LaTeX\  markup
into hypertext links between the different sections of the document,
so that references to equations, tables, footnotes, and section
headings are in place, and bibliographic references and figures
refer to the bibliography entry or figure caption.

The macros developed thus far use standard naming conventions
for the underlying structures in \LaTeX\ and other standard
macro packages, so that appending \#equation.2.3, \#page.7,
\#figure.4, \#table.2, etc. to the URL for any \TeX{} file processed
with these packages will go to the right place, allowing
easy hypertext reference to the internal structure of other
documents.

\subsection*{How do I stay in contact?}
The Hypertex discussion group is
a mailing list based at \FTP|snorri.chem.washington.edu| which I
maintain. Send me e-mail (\Email|asmith@mammoth.chem.washington.edu|)
if you want to join the list, or send queries directly to the mailing
list: \Email|hypertex@snorri.chem.washington.edu|.
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