%&latex
% $Id: tds.tex,v 1.43 2004/06/23 17:24:42 karl Exp $
\NeedsTeXFormat{LaTeX2e} % compatibility with 2.09 is too painful
\documentclass{tdsguide}

\tdsVersion{1.1}

\title{A Directory Structure for \TeX{} Files}
\author{TUG Working Group on a \TeX{} Directory Structure (TWG-TDS)}

\begin{document}

\maketitle

\begin{legalnotice}

Copyright {\copyright} 1994, 1995, 1996, 1997, 1998, 1999, 2003, 2004
\TeX{} Users Group.

Permission to use, copy, and distribute this document \emphasis{without
modification} for any purpose and without fee is hereby granted,
provided that this notice appears in all copies.  It is provided ``as
is'' without expressed or implied warranty.

Permission is granted to copy and distribute modified versions of this
document under the conditions for verbatim copying, provided that the
modifications are clearly marked and the document is not represented as
the official one.

This document is available on any \abbr{ctan} host
(see Appendix~\ref{sec:Related references}).
Please send questions or suggestions by email to
\email|tds@tug.org|.  We welcome all comments.   This is version
\the\tdsVersion.

\end{legalnotice}


\tableofcontents


\newpage
\section{Introduction}

\TeX{} is a powerful, flexible typesetting system used by many people
around the world.  It is extremely portable and runs on virtually all
operating systems.  One unfortunate side effect of \TeX{}'s flexibility,
however, is that there has been no single ``right'' way to install it.
This has resulted in many sites having different installed arrangements.

The primary purpose of this document is to describe a standard \TeX{}
Directory Structure (\abbr{TDS}): a directory hierarchy for macros,
fonts, and the other implementation-independent \TeX{} system files.  As
a matter of practicality, this document also suggests ways to
incorporate the rest of the \TeX{} files into a single structure.  The
\abbr{TDS} has been designed to work on all modern systems.  In
particular, the Technical Working Group (\abbr{TWG}) believes it is usable
under Mac\abbr{OS}, \abbr{ms-dos}, \abbr{os/2}, Unix, \abbr{vms}, and
Windows \abbr{nt}\@.  We hope that administrators and developers of both
free and commercial \TeX{} implementations will adopt this standard.

This document is intended both for the \TeX{} system administrator at a
site and for people preparing \TeX{} distributions---everything from a
complete runnable system to a single macro or style file. It may also
help \TeX{} users find their way around systems organized this way.  It
is not a tutorial: we necessarily assume knowledge of the many parts of
a working \TeX{} system. If you are unfamiliar with any of the programs
or file formats we refer to, consult the references in
Appendix~\ref{sec:Related references}.


\subsection{History}

Version 1.0 of the \abbr{TDS} was released in February 2003.

Version 1.1 was released in June 2004, with the following non-editorial
changes:

\begin{itemize-squeeze}
\item Inputs for \TeX{} extensions included under \path|tex|, instead
      of in their own top-level directories (Section~\ref{sec:Extensions})
\item New top-level directory \path|scripts| (Section~\ref{sec:Scripts}).
\item New subdirectories \path|lig|, \path|opentype|,
      \path|truetype|, and \path|type3| under \path|fonts|
      (Section~\ref{sec:Fonts}).
\item \path|enc|, \path|lig|, and \path|map| all use
      \replaceable{syntax}\path|/|\replaceable{package} subdirectories
      (Section~\ref{sec:Fonts}).
\item \path|pfm| files specified to go under \path|type1|, and
      \path|inf| files under \path|afm| (Section~\ref{sec:Fonts}).
\end{itemize-squeeze}


\subsection{The role of the \abbr{TDS}}

The role of the \abbr{TDS} is to stabilize the organization of
\TeX{}-related software packages that are installed and in use, possibly
on multiple platforms simultaneously.

At first glance, it may seem that the Comprehensive \TeX{} Archive
Network (\abbr{ctan}) fulfills at least part of this role, but this is
not the case.  The role of \abbr{ctan} is to simplify archiving and
distribution, not installation and use.

In fact, the roles of the \abbr{TDS} and \abbr{ctan} are frequently in
conflict, as we will see.  For distribution, many different types of
files must be combined into a single unit; for use, it is traditional to
segregate files (even similar files) from a single package into
separate, occasionally distant, directories.


\subsection{Conventions}

In this document, ``\path|/|'' is used to separate filename components;
for example, \path|texmf/fonts|.  This is the Unix convention but the
ideas are in no way Unix-specific.

In this document, ``\TeX{}'' generally means the \TeX{} system, including
\MF{}, \abbr{DVI} drivers, utilities, etc., not just the \TeX{}
program itself.

The word ``package'' in this document has its usual meaning: a set of
related files distributed, installed, and maintained as a unit.  This is
\emphasis{not} a \LaTeXe{} package, which is a style file supplementing
a document class.

We use the following typographic conventions:

\begin{description}

\item[\literal{literal}] Literal text such as \literal{filename} is
typeset in typewriter type.

\item[\replaceable{replaceable}] Replaceable text such as
\replaceable{package}, identifying a class of things, is typeset in
italics inside angle brackets.

\end{description}


\section{General}

This section describes common properties throughout the \abbr{TDS} tree.

\subsection{Subdirectory searching}
\label{sec:Subdirectory searching}

Older \TeX{} installations store large numbers of related files in single
directories, for example, all \path|TFM| files and\slash or all \TeX{}
input files.

This monolithic arrangement hinders maintenance of a \TeX{} system: it
is difficult to determine what files are used by what packages, what
files need to be updated when a new version is installed, or what files
should be deleted if a package is removed.  It is also a source of error
if two or more packages happen to have input files with the same name.

Therefore, the \abbr{TWG} felt each package should be in a separate
directory. But we recognized that explicitly listing all directories to
be searched would be unbearable.  A site may wish to install dozens of
packages.  Aside from anything else, listing that many directories would
produce search paths many thousands of characters long, overflowing the
available space on some systems.

Also, if all directories are explicitly listed, installing or removing a
new package would mean changing a path as well as installing or removing
the actual files.  This would be a time-consuming and error-prone
operation, even with implementations that provide some way to specify
the directories to search at runtime.  On systems without runtime
configuration, it would require recompiling software, an intolerable
burden.

As a result, the \abbr{TWG} concluded that a comprehensive \abbr{TDS}
requires implementations to support some form of implicit subdirectory
searching.  More precisely, implementations must make it possible to
specify that \TeX{}, \MF{}, and their companion utilities search in both
a specified directory and recursively through all subdirectories of that
directory when looking for an input file.  Other forms of subdirectory
searching, for example recursive-to-one-level searches, may also be
provided.  We encourage implementors to provide subdirectory searching
at the option of the installer and user for all paths.

The \abbr{TDS} does not specify a syntax for specifying recursive
searching, but we encourage implementors to provide interoperability
(see Section~\ref{sec:More on subdirectory searching}).


\subsection{Rooting the tree}
\label{sec:Rooting the tree}

In this document, we shall designate the root \abbr{TDS} directory by
`\texmf{}' (for ``\TeX{} and \MF{}''). We recommend using that name
where possible, but the actual name of the directory is up to the
installer. On \abbr{pc} networks, for example, this could map to a
logical drive specification such as \path|T:|.

Similarly, the location of this directory on the system is
site-dependent.  It may be at the root of the file system; on Unix
systems, \path|/usr/local/share|, \path|/usr/local|,
\path|/usr/local/lib|, and \path|/opt| are common choices.

The name \texmf{} was chosen for several reasons: it reflects the fact
that the directory contains files pertaining to an entire \TeX{} system
(including \MF{}, \MP{}, \BibTeX{}, etc.), not just \TeX{} itself; and it
is descriptive of a generic installation rather than a particular
implementation.

A site may choose to have more than one \abbr{TDS} hierarchy installed
(for example, when installing an upgrade). This is perfectly legitimate.


\subsection{Local additions}
\label{sec:Local additions}

The \abbr{TDS} cannot specify precisely when a package is or is not a
``local addition''. Each site must determine this according to its own
conventions.  At the two extremes, one site might wish to consider
``nonlocal'' all files not acquired as part of the installed \TeX{}
distribution; another site might consider ``local'' only those files
that were actually developed at the local site and not distributed
elsewhere.

We recognize two common methods for local additions to a distributed
\texmf{} tree. Both have their place; in fact, some sites employ
both simultaneously:

\begin{enumerate}

\item A completely separate tree which is a \abbr{TDS} structure
itself; for example, \path|/usr/local/umbtex| at the University of
Massachusetts at Boston. This is another example of the multiple
\texmf{} hierarchies mentioned in the previous section.

\item A directory named `\path|local|' at any appropriate level, for
example, in the \replaceable{format}, \replaceable{package}, and
\replaceable{supplier} directories discussed in the following sections.
The \abbr{TDS} reserves the directory name \path|local| for this
purpose.

We recommend using \path|local| for site-adapted configuration files,
such as \path|language.dat| for the Babel package or \path|graphics.cfg|
for the graphics package.  Unmodified configuration files from a package
should remain in the package directory. The intent is to separate
locally modified or created files from distribution files, to ease
installing new releases.

\end{enumerate}

One common case of local additions is dynamically generated files, e.g.,
\abbr{PK} fonts by the \path|mktexpk| script (which originated in
\application{Dvips} as \path|MakeTeXPK|).  A site may store the
generated files directly in any of:
\begin{itemize-squeeze}
\item their standard location in the main \abbr{TDS} tree (if it can be
made globally writable);

\item an alternative location in the main \abbr{TDS} tree (for
example, under \path|texmf/fonts/tmp|);

\item a second complete \abbr{TDS} tree (as outlined above);

\item any other convenient directory (perhaps under
\path|/var|, for example \path|/var/spool/fonts|).

\end{itemize-squeeze}

No one solution will be appropriate for all sites.


\subsection{Duplicate filenames}
\label{sec:Duplicate filenames}

Different files by the same name may exist in a \abbr{TDS} tree. The
\abbr{TDS} generally leaves unspecified which of two files by the same
name in a search path will be found, so generally the only way to
reliably find a given file is for it to have a unique name.  However,
the \abbr{TDS} requires implementations to support the following
exceptions:

\begin{itemize}

\item Names of \TeX{} input files must be unique within each first-level
subdirectory of \path|texmf/tex| and \path|texmf/tex/generic|, but not
within all of \path|texmf/tex|; i.e., different \TeX{} formats may have
files by the same name. (Section~\ref{sec:Macros} discusses this
further.)  Thus, no single format-independent path specification, such
as a recursive search beginning at \path|texmf/tex| specifying no other
directories, suffices.  So implementations must provide format-dependent
path specifications, for example via wrapper scripts or configuration
files.

\item Many font files will have the same name (e.g., \path|cmr10.pk|),
as discussed in Section~\ref{sec:Valid font bitmaps}.  Implementations
must distinguish these files by mode and resolution.

\end{itemize}

All implementations we know of already have these capabilities.

One place where duplicate names are likely to occur is not an exception:

\begin{itemize}

\item Names of \MF{} input files (as opposed to bitmaps) must be unique
within all of \path|texmf/fonts|. In practice, this is a problem with
some variants of Computer Modern which contain slightly modified files
named \path|punct.mf|, \path|romanl.mf|, and so on. We believe the only
feasible solution is to rename the derivative files to be
unique.

\end{itemize}


\section{Top-level directories}
\label{sec:Top-level directories}

The directories under the \texmf{} root identify the major components of
a \TeX{} system (see Section~\ref{sec:Summary} for a summary).  A site
may omit any unneeded directories.

Although the \abbr{TDS} by its nature can specify precise locations only
for implementation-independent files, we recognize that installers may
well wish to place other files under \texmf{} to simplify administration
of the \TeX{} tree, especially if it is maintained by someone other than
the system administrator.  Therefore, additional top-level directories
may be present.

The top-level directories specified by the \abbr{TDS} are:

\begin{description}
\item[\path|tex|]
for \TeX{} files (Section~\ref{sec:Macros}).

\item[\path|fonts|]
for font-related files (Section~\ref{sec:Fonts}).

\item[\path|metafont|]
for \MF{} files which are not fonts (Section~\ref{sec:Non-font MF files}).

\item[\path|metapost|]
for \MP{} files (Section~\ref{sec:MetaPost}).

\item[\path|bibtex|]
for \BibTeX{} files (Section~\ref{sec:BibTeX}).

\item[\path|scripts|]
for platform-independent executables (Section~\ref{sec:Scripts}).

\item[\path|doc|]
for user documentation (Section~\ref{sec:Documentation}).

\item[\path|source|] for sources.  This includes both traditional
program sources (for example, \application{Web2C} sources go in
\path|texmf/source/web2c|) and, e.g., \LaTeX{} \path|dtx| sources (which
go in \path|texmf/source/latex|). The \abbr{TDS} leaves unspecified any
structure under \path|source|.

\path|source| is intended for files which are not needed at runtime by
any \TeX{} program; it should not be included in any search path. For
example, \path|plain.tex| does not belong under \path|texmf/source|,
even though it is a ``source file'' in the sense of not being derived
from another file. (It goes in \path|texmf/tex/plain/base|, as explained
in Section~\ref{sec:Macros}).

\item[\replaceable{implementation}] for implementations (examples:
\path|emtex|, \path|vtex|, \path|web2c|), to be used for whatever
purpose deemed suitable by the implementor or \TeX{} administrator.
That is, files that cannot be shared between implementations, such as
pool files (\path|tex.pool|) and memory dump files (\path|plain.fmt|) go
here, in addition to implementation-wide configuration files.  See
Section~\ref{sec:Example implementation-specific trees} for examples of
real \replaceable{implementation} trees.

Such implementation-specific configuration files should \emphasis{not}
be located using the main \TeX{} input search path (e.g.,
\path|TEXINPUTS|).  This must be reserved for files actually read by a
\TeX{} engine.  See Section~\ref{sec:Extensions}.

\item[\replaceable{program}] for program-specific input and
configuration files for any \TeX{}-related programs (examples:
\path|mft|, \path|dvips|).  In fact, the \path|tex|, \path|metafont|,
\path|metapost|, and \path|bibtex| items above may all be seen as
instances of this case.

\end{description}


\subsection{Macros}
\label{sec:Macros}

\TeX{} macro files shall be stored in separate directories, segregated
by \TeX{} format and package name (we use `format' in its traditional
\TeX{} sense to mean a usefully \path|\dump|-able package):
\begin{ttdisplay}
texmf/tex/\replaceable{format}/\replaceable{package}/
\end{ttdisplay}

\begin{description}

\item[\replaceable{format}] is a format name (examples: \path|amstex|,
\path|latex|, \path|plain|, \path|texinfo|).

The \abbr{TDS} allows distributions that can be used as either formats or
packages (e.g., Texinfo, Eplain) to be stored at either level, at the
option of the format author or \TeX{} administrator. We recommend that
packages used as formats at a particular site be stored at the
\replaceable{format} level: by adjusting the \TeX{} inputs search path,
it will be straightforward to use them as macro packages under another
format, whereas placing them in another tree completely obscures their
use as a format.

The \abbr{TDS} reserves the following \replaceable{format} names:

\begin{itemize}

\item \path|generic|, for input files that are useful across a wide
range of formats (examples: \path|null.tex|, \path|path.sty|).
Generally, this means any format that uses the category codes of Plain
\TeX{} and does not rely on any particular format.  This is in contrast
to those files which are useful only with Plain \TeX{} (which go under
\path|texmf/tex/plain|), e.g., \path|testfont.tex| and \path|plain.tex|
itself.

\item \path|local|, for local additions. See Section~\ref{sec:Local
additions}.

\end{itemize}

Thus, for almost every format, it is necessary to search at least the
\replaceable{format} directory and then the \path|generic| directory (in
that order).  Other directories may need to be searched as well,
depending on the format.  When using \AMSTeX{}, for example, the
\path|amstex|, \path|plain|, and \path|generic| directories should be
searched, because \AMSTeX{} is compatible with Plain.

\item[\replaceable{package}] is a \TeX{} package name (examples:
\path|babel|, \path|texdraw|).

In the case where a format consists of only a single file and has no
auxiliary packages, that file can simply be placed in the
\replaceable{format} directory, instead of
\replaceable{format}\path|/base|.  For example, Texinfo may go in
\path|texmf/tex/texinfo/texinfo.tex|, not
\path|texmf/tex/texinfo/base/texinfo.tex|.

The \abbr{TDS} reserves the following \replaceable{package} names:

\begin{itemize}

\item \path|base|, for the base distribution of each format,
including files used by \iniTeX{} when dumping format files.  For
example, in the standard \LaTeX{} distribution, the \path|ltx| files
created during the build process.  Another example: the \path|.ini|
driver files for formats used by \TeX{} Live and other distributions.

\item \path|hyphen|, for hyphenation patterns, including the original
American English \path|hyphen.tex|.  These are typically used only by
\iniTeX{}.  In most situations, this directory need exist only under the
\literal{generic} format.

\item \path|images|, for image input files, such as Encapsulated
PostScript figures. Although it is somewhat non-intuitive for these to
be under a directory named ``\path|tex|'', \TeX{} needs to read these
files to glean bounding box or other information.  A mechanism for
sharing image inputs between \TeX{} and other typesetting programs
(e.g., Interleaf, FrameMaker) is beyond the scope of the
\abbr{TDS}\@. In most situations, this directory need exist only under
the \literal{generic} format.

\item \path|local|, for local additions and configuration files. See
Section~\ref{sec:Local additions}.

\item \path|misc|, for packages that consist of a single file.  An
administrator or package maintainer may create directories for
single-file packages at their discretion, instead of using \path|misc|.

\end{itemize}

\end{description}


\subsubsection{Extensions}
\label{sec:Extensions}

\TeX{} has spawned many companion and successor programs (``engines''),
such as \abbr{PDF}\TeX{}, Omega, and others.  The \abbr{TDS} specifies
that the input files for such programs (using a \TeX{}-like syntax) be
placed within the top-level \path|tex| directory, either at the top
level or within a format subdirectory, even though the original \TeX{}
program may not be able to read them.  For example:

\begin{ttdisplay}
texmf/tex/aleph
texmf/tex/enctex
\end{ttdisplay}

This is a change from \abbr{TDS}~1.0, which specified top-level
\replaceable{extension} directories for each such program.  We felt the
new approach is preferable, because:

\begin{itemize}

\item Authors of relevant packages typically make their code detect the
engine being used, and issue error messages or adapt to circumstances
appropriately.  Furthermore, as a package matures, it may support
multiple engines.  Thus, a package could conceivably be placed in any of
several top-level directories, at different times.  Putting all packages
under the top-level \path|tex| directory provides a stable location over
time.

\item Users need to be able to switch between engines, and configuring
different search paths for each engine is difficult and error-prone.

\end{itemize}

Thus, in practice, having different top-level directories caused
difficulties for everyone involved---users, package authors, site
administrators, and system distributors.

Please contrast this approach with the \replaceable{implementation}
top-level subdirectory (Section~\ref{sec:Top-level directories}), which
is to be used for configuration files that (presumably) do not use
\TeX{} syntax and in any case should not be found along the main \TeX{}
input search path.


\subsection{Fonts}
\label{sec:Fonts}

Font files are stored in separate directories, segregated by file type,
and then (in most cases) font supplier and typeface.  \abbr{PK} and
\abbr{GF} files need additional structure, as detailed in the next
section.

\begin{ttdisplay}
texmf/fonts/\replaceable{type}/\replaceable{supplier}/\replaceable{typeface}/
texmf/fonts/enc,lig,map/\replaceable{subpath}/
\end{ttdisplay}

\begin{description}

\item[\replaceable{type}] is the type of font file. The \abbr{TDS}
reserves the following \replaceable{type} names for common \TeX{} file
types:

\begin{itemize-squeeze}
\item \path|afm|, for Adobe font metrics, and \path|inf| files.
\item \path|gf|, for generic font bitmap files.
\item \path|opentype|, for OpenType fonts.
\item \path|pk|, for packed bitmap files.
\item \path|source|, for font sources (\MF{} files, property lists, etc.).
\item \path|tfm|, for \TeX{} font metric files.
\item \path|truetype|, for TrueType fonts.
\item \path|type1|, for PostScript Type 1 fonts (in \path|pfa|,
      \path|pfb|, or any other format), and \path|pfm| files. 
\item \path|type3|, for PostScript Type 3 fonts.
\item \path|vf|, for virtual fonts.
\end{itemize-squeeze}

The \abbr{TDS} also reserves the names \path|enc|, \path|lig|, and
\path|map| for font encoding, ligature, and mapping files, respectively.
All of these directories are structured the same way, with
\replaceable{syntax} subdirectories, and then \replaceable{package}
subsubdirectories.  Each of these file types is intended to be searched
along its own recursively-searched path.  The names of the actual files
must be unique within their subtree, as usual.  Examples:
\begin{ttdisplay}
fonts/map/dvipdfm/updmap/dvipdfm.map  
fonts/map/dvips/lm/lm.map
fonts/enc/dvips/base/8r.enc
\end{ttdisplay}

The Fontname and Dvips packages have more examples of the \path|enc| and
\path|map| types.  The \path|afm2pl| program uses \path|lig| files.  

\path|pfm| files are included in the \path|type1| directory, instead of
being given their own directory, for two reasons: 1)~a \path|.pfm| file
is always an adjunct to a given \path|.pfb| file; 2)~they must be
installed from the same directory for Windows programs other than \TeX{}
to use them.

\path|inf| files are included in the \path|afm| directory, since
an \path|inf| and \path|afm| file can be used to generate a \path|pfm|.
(Unfortunately, Adobe Type Manager and perhaps other software requires
that the \path|pfb| be in the same directory as \path|afm| and
\path|inf| for installation.)

As usual, a site may omit any of these directories that are unnecessary.
\path|gf| is a particularly likely candidate for omission.

\item[\replaceable{supplier}] is a name identifying font source
(examples: \path|adobe|, \path|ams|, \path|public|). The \abbr{TDS}
reserves the following \replaceable{supplier} names:

\begin{itemize}

\item \path|ams|, for the American Mathematical Society's \AmS{}-fonts
collection.

\item \path|local|, for local additions. See Section~\ref{sec:Local additions}.

\item \path|public|, for freely redistributable fonts where the supplier
neither (1)~requested their own directory (e.g., \path|ams|), nor
(2)~also made proprietary fonts (e.g., \path|adobe|).  It does not
contain all extant freely distributable fonts, nor are all files therein
necessarily strictly public domain.

\item \path|tmp|, for dynamically-generated fonts, as is traditional on
some systems. It may be omitted if unnecessary, as usual.

\end{itemize}


\item[\replaceable{typeface}] is the name of a typeface family
(examples: \path|cm|, \path|euler|, \path|times|). The \abbr{TDS}
reserves the following \replaceable{typeface} names:

\begin{itemize}

\item \path|cm| (within \path|public|), for the 75 fonts defined in
\citetitle{Computers and Typesetting, Volume~E}.

\item \path|latex| (within \path|public|), for those fonts distributed
with \LaTeX{} in the base distribution.

\item \path|local|, for local additions. See Section~\ref{sec:Local additions}.

\end{itemize}

\end{description}

Some concrete examples:
\begin{ttdisplay}
texmf/fonts/source/public/pandora/pnr10.mf
texmf/fonts/tfm/public/cm/cmr10.tfm
texmf/fonts/type1/adobe/utopia/putr.pfa
\end{ttdisplay}

For complete supplier and typeface name lists, consult
\citetitle{Filenames for \TeX{} fonts} (see Appendix~\ref{sec:Related
references}).

\subsubsection{Font bitmaps}

Font bitmap files require two characteristics in addition to the above
to be uniquely identifiable: (1)~the type of device (i.e., mode) for
which the font was created; (2)~the resolution of the bitmap.

Following common practice, the \abbr{TDS} segregates fonts with
different device types into separate directories.  See \path|modes.mf|
in Appendix~\ref{sec:Related references} for recommended mode names.

Some printers operate at more than one resolution (e.g., at 300\,dpi and
600\,dpi), but each such resolution will necessarily have a different
mode name. Nothing further is needed, since implicit in the \TeX{}
system is the assumption of a single target resolution.

Two naming strategies are commonly used to identify the resolution of
bitmap font files.  On systems that allow long filenames (and in the
original \MF{} program itself), the resolution is included in the
filename (e.g., \path|cmr10.300pk|).  On systems which do not support
long filenames, fonts are generally segregated into directories by
resolution (e.g., \path|dpi300/cmr10.pk|).

Because the \abbr{TDS} cannot require long filenames, we must use the
latter scheme for naming fonts. So we have two more subdirectory
levels under \path|pk| and \path|gf|:

\begin{ttdisplay}
texmf/fonts/pk/\replaceable{mode}/\replaceable{supplier}/\replaceable{typeface}/dpi\replaceable{nnn}/
texmf/fonts/gf/\replaceable{mode}/\replaceable{supplier}/\replaceable{typeface}/dpi\replaceable{nnn}/
\end{ttdisplay}

\begin{description}

\item[\replaceable{mode}] is a name which identifies the device type
(examples: \path|cx|, \path|ljfour|, \path|modeless|).  Usually, this is
the name of the \MF{} mode used to build the \abbr{PK} file.  For fonts
rendered as bitmaps by a program that does not distinguish between
different output devices, the \replaceable{mode} name shall be simply
\path|modeless|.  The \replaceable{mode} level shall not be omitted,
even if only a single mode happens to be in use.

\item[\path|dpi|\replaceable{nnn}] specifies the resolution of the font
(examples: \path|dpi300|, \path|dpi329|).  `\literal{dpi}' stands for
dots per inch, i.e., pixels per inch. We recognize that pixels per
millimeter is used in many parts of the world, but dpi is too
traditional in the \TeX{} world to consider changing now.

The integer \replaceable{nnn} is to be calculated as if using \MF{}
arithmetic and then rounded; i.e., it is the integer \MF{} uses in its
output \path|gf| filename.  We recognize small differences in the
resolution are a common cause of frustration among users, however, and
recommend implementors follow the level~0 \abbr{DVI} driver standard
(see Appendix~\ref{sec:Related references}) in bitmap font searches by
allowing a fuzz of $\pm0.2$\% (with a minimum of $1$) in the
\replaceable{dpi}.

\end{description}

Implementations may provide extensions to the basic naming scheme, such
as long filenames (as in the original \MF{}) and font library files (as
in em\TeX{}'s \path|.fli| files), provided that the basic scheme is also
supported.

\subsubsection{Valid font bitmaps}
\label{sec:Valid font bitmaps}

The \abbr{TWG} recognizes that the use of short filenames has many
disadvantages.  The most vexing is that it results in the creation of
dozens of different files with the same name.  At a typical site,
\path|cmr10.pk| will be the filename for Computer Modern Roman 10\,pt at
5--10 magnifications for 2--3 modes. (Section~\ref{sec:Duplicate
filenames} discusses duplicate filenames in general.)

To minimize this problem, we strongly recommend that \abbr{PK} files
contain enough information to identify precisely how they were created:
at least the mode, base resolution, and magnification used to create the
font.

This information is easy to supply: a simple addition to the local modes
used for building the fonts with \MF{} will automatically provide the
required information.  If you have been using a local modes file derived
from (or that is simply) \path|modes.mf| (see Appendix~\ref{sec:Related
references}), the required information is already in your \abbr{PK}
files.  If not, a simple addition based on the code found in
\path|modes.mf| can be made to your local modes file and the \abbr{PK}
files rebuilt.


\subsection{Non-font \MF{} files}
\label{sec:Non-font MF files}

Most \MF{} input files are font programs or parts of font programs and
are thus covered by the previous section. However, a few non-font input
files do exist. Such files shall be stored in:

\begin{ttdisplay}
texmf/metafont/\replaceable{package}/
\end{ttdisplay}

\replaceable{package} is the name of a
\MF{} package (for example, \path|mfpic|).

The \abbr{TDS} reserves the following \replaceable{package} names:

\begin{itemize}

\item \path|base|, for the standard \MF{} macro files as described in
\citetitle{The \MF{}book}, such as \path|plain.mf| and \path|expr.mf|.

\item \path|local|, for local additions. See Section~\ref{sec:Local additions}.

\item \path|misc|, for \MF{} packages consisting of only a single file
(for example, \path|modes.mf|).  An administrator or package maintainer
may create directories for single-file packages at their discretion,
instead of using \path|misc|.

\end{itemize}


\subsection{\MP{}}
\label{sec:MetaPost}

\MP{} is a picture-drawing language developed by John Hobby, derived
from Knuth's \MF{}. Its primary purpose is to output Encapsulated \PS{}
instead of bitmaps.

\MP{} input files and the support files for \MP{}-related utilities
shall be stored in:

\begin{ttdisplay}
texmf/metapost/\replaceable{package}/
\end{ttdisplay}

\replaceable{package} is the name of a \MP{} package.  At the present
writing none exist, but the \abbr{TWG} thought it prudent to leave room
for contributed packages that might be written in the future.

The \abbr{TDS} reserves the following \replaceable{package} names:

\begin{itemize}

\item \path|base|, for the standard \MP{} macro files, such as
\path|plain.mp|, \path|mfplain.mp|, \path|boxes.mp|, and
\path|graph.mp|.  This includes files used by \iniMP{} when dumping mem
files containing preloaded macro definitions.

\item \path|local|, for local additions. See Section~\ref{sec:Local
additions}.

\item \path|misc|, for \MP{} packages consisting of only a single file.
An administrator or package maintainer may create directories for
single-file packages at their discretion, instead of using \path|misc|.

\item \path|support|, for additional input files required by \MP{}
utility programs, including a font map, a character adjustment table,
and a subdirectory containing low-level \MP{} programs for rendering
some special characters.

\end{itemize}


\subsection{\BibTeX{}}
\label{sec:BibTeX}

\BibTeX{}-related files shall be stored in:

\begin{ttdisplay}
texmf/bibtex/bib/\replaceable{package}/
texmf/bibtex/bst/\replaceable{package}/
\end{ttdisplay}

The \path|bib| directory is for \BibTeX{} database (\path|.bib|) files,
the \path|bst| directory for style (\path|.bst|) files.

\replaceable{package} is the name of a \BibTeX{} package.  The
\abbr{TDS} reserves the following \replaceable{package} names (the same
names are reserved under both \path|bib| and \path|bst|):

\begin{itemize}

\item \path|base|, for the standard \BibTeX{} databases and styles, such
as \path|xampl.bib|, \path|plain.bst|.

\item \path|local|, for local additions. See Section~\ref{sec:Local
additions}.

\item \path|misc|, for \BibTeX{} packages consisting of only a single
file.  An administrator or package maintainer may create directories for
single-file packages at their discretion, instead of using \path|misc|.

\end{itemize}


\subsection{Scripts}
\label{sec:Scripts}

The top-level \path|scripts| directory is for platform-independent
executables, such as Perl, Python, and shell scripts, and Java class
files.  Subdirectories under \path|scripts| are package names.  This
eases creating distributions, by providing a common place for such
platform-independent programs.

The intent is not for all such directories to be added to a user's
command search path, which would be quite impractical.  Rather, these
executables are primarily for the benefit of wrapper scripts in whatever
executable directory a distribution may provide (which is not specified
by the \abbr{TDS}).  

Truly auxiliary scripts which are invoked directly by other programs,
rather than wrapper scripts, may also be placed here.  That is,
\path|scripts| also serves as a platform-independent analog of the
standard Unix \path|libexec| directory.

We recommend using extensions specifying the language (such as
\path|.pl|, \path|.py|, \path|.sh|) on these files, to help uniquely
identify the name.  Since the intent of the \abbr{TDS} is for programs
in \path|scripts| not to be invoked directly by users, this poses no
inconvenience.

For example, in the \TeX{} Live distribution, the Con\TeX{}t user-level
program \path|texexec| can exist as a small wrapper script in each
\path|bin/|\replaceable{platform}\path|/texexec| (which is outside the
\path|texmf| tree), which merely finds and calls
\path|texmf/scripts/context/perl/texexec.pl|.

Examples:
\begin{ttdisplay}
scripts/context/perl/texexec.pl
scripts/context/ruby/examplex.rb
scripts/thumbpdf/thumbpdf.pl
\end{ttdisplay}

The \abbr{TDS} does not specify a location for platform-dependent
binary executables, whether auxiliary or user-level.


\subsection{Documentation}
\label{sec:Documentation}

Most packages come with some form of documentation: user manuals,
example files, programming guides, etc.  In addition, many independent
files not part of any macro or other package have been created to
describe various aspects of the \TeX{} system.

The \abbr{TDS} specifies that these additional documentation files shall
be stored in a structure that parallels to some extent the
\path|fonts| and \path|tex| directories, as follows:

\begin{ttdisplay}
texmf/doc/\replaceable{category}/...
\end{ttdisplay}

\replaceable{category} identifies the general topic of documentation
that resides below it; for example, a \TeX{} format name (\path|latex|),
program name (\path|bibtex|, \path|tex|), language (\path|french|,
\path|german|), a file format (\path|info|, \path|man|), or other system
components (\path|web|, \path|fonts|).

One possible arrangement is to organize \path|doc| by language, with all
the other category types below that.  This helps users find
documentation in the language(s) in which they are fluent.  Neither this
nor any other particular arrangement is required, however.

Within each \replaceable{category} tree for a \TeX{} format, the
directory \path|base| is reserved for base documentation distributed by
the format's maintainers.

The \abbr{TDS} reserves the following category names:

\begin{itemize}

\item \path|general|, for standalone documents not specific to any
particular program (for example, Joachim Schrod's \citetitle{Components
of \TeX{}}).

\item \path|help|, for meta-information, such as \abbr{faq}'s, 
the \TeX{} Catalogue, etc.

\item \path|info|, for processed Texinfo documents.  (Info files, like
anything else, may also be stored outside the \abbr{TDS}, at the
installer's option.)

\item \path|local|, for local additions. See Section~\ref{sec:Local
additions}.

\end{itemize}

The \path|doc| directory is intended for implementation-independent and
operating system-independent documentation
files. Implementation-dependent files are best stored elsewhere, as
provided for by the implementation and/or \TeX{} administrator (for
example, \abbr{VMS} help files under \path|texmf/vms/help|).

The documentation directories may contain \TeX{} sources, \abbr{DVI}
files, \PS{} files, text files, example input files, or any other useful
documentation format(s).

See Section~\ref{sec:Documentation tree summary} for a summary.


\newpage
\section{Summary}
\label{sec:Summary}

A skeleton of a \abbr{TDS} \texmf{} directory tree.  This is not to
imply these are the only entries allowed.  For example, \path|local| may
occur at any level.

\begin{tdsSummary}
  bibtex/           \BibTeX{} input files
  . bib/            \BibTeX{} databases
  . . base/         base distribution (e.g., \path|xampl.bib|)
  . . misc/         single-file databases
  . <package>/      name of a package
  . bst/            \BibTeX{} style files
  . . base/         base distribution (e.g., \path|plain.bst|, \path|acm.bst|)
  . . misc/         single-file styles
  . <package>/      name of a package
  doc/              see Section~\ref{sec:Documentation} and the summary below
  fonts/            font-related files
  . <type>/         file type (e.g., \path|pk|)
  . . <mode>/       type of output device (for \path|pk| and \path|gf| only)
  . . . <supplier>/     name of a font supplier (e.g., \path|public|)
  . . . . <typeface>/   name of a typeface (e.g., \path|cm|)
  . . . . . dpi<nnn>/   font resolution (for \path|pk| and \path|gf| only)
  <implementation>/ \TeX{} implementations, by name (e.g., \path|emtex|)
  local/            files created or modified at the local site
  metafont/         \MF{} (non-font) input files
  . base/           base distribution (e.g., \path|plain.mf|)
  . misc/           single-file packages (e.g., \path|modes.mf|)
  . <package>/      name of a package (e.g., \path|mfpic|)
  metapost/         \MP{} input and support files
  . base/           base distribution (e.g., \path|plain.mp|)
  . misc/           single-file packages
  . <package>/      name of a package
  . support/        support files for \MP{}-related utilities
  mft/              \path|MFT| inputs (e.g., \path|plain.mft|)
  <program>/        \TeX{}-related programs, by name (e.g., \path|dvips|)
  source/           program source code by name (e.g., \path|latex|, \path|web2c|)
  tex/              \TeX{} input files
  . <engine>/       name of an engine (e.g., \path|aleph|); can also be lower
  . <format>/       name of a format (e.g., \path|plain|)
  . . base/         base distribution for format (e.g., \path|plain.tex|)
  . . misc/         single-file packages (e.g., \path|webmac.tex|)
  . . local/        local additions to or local configuration files for \replaceable{format}
  . . <package>/    name of a package (e.g., \path|graphics|, \path|mfnfss|)
  . generic/        format-independent packages
  . . hyphen/       hyphenation patterns (e.g., \path|hyphen.tex|)
  . . images/       image input files (e.g., Encapsulated PostScript)
  . . misc/         single-file format-independent packages (e.g., \path|null.tex|).
  . . <package>/    name of a package (e.g., \path|babel|)
\end{tdsSummary}


\newpage
\subsection{Documentation tree summary}
\label{sec:Documentation tree summary}

An example skeleton of a \abbr{TDS} directory tree under
\path|texmf/doc|.  This is not to imply these are the only entries
allowed, or that this structure must be followed precisely for the
entries listed.

As mentioned, the \path|texmf/doc| tree may be organized by language, so
that all documentation in French, say, is in a \path|french|
subdirectory.  In that case, the example structure here would be in a
given language directory.

\begin{tdsSummary}
  ams/
  . amsfonts/       \path|amsfonts.faq|, \path|amfndoc|
  . amslatex/       \path|amslatex.faq|, \path|amsldoc|
  . amstex/         \path|amsguide|, \path|joyerr|
  bibtex/           \BibTeX{}
  . base/           \path|btxdoc.tex|
  fonts/
  . fontname/       \citetitle{Filenames for \TeX{} fonts}
  . oldgerm/        \path|corkpapr|
  <format>/         name of a \TeX{} format (e.g., \path|generic|, \path|latex|)
  . base/           for the base distribution
  . misc/           for contributed single-file package documentation
  . <package>/      for \emphasis{package}
  general/          across programs, generalities
  . errata/         \path|errata|, \path|errata[1-8]|
  . texcomp/        \citetitle{Components of \TeX{}}
  help/             meta-information
  . ctan/           info about \abbr{ctan} mirror sites
  . faq/            \abbr{faq}s of \path|comp.text.tex|, etc.
  info/             \abbr{gnu} Info files, made from Texinfo sources
  latex/            example of \replaceable{format}
  . base/           \path|ltnews*|, \path|*guide|, etc.
  . graphics/       \path|grfguide|
  local/            site-specific documentation
  man/              Unix man pages
  <program>/        \TeX{}-related programs, by name (examples follow)
  metafont/         \path|mfbook.tex|, \path|metafont-for-beginners|, etc.
  metapost/         \path|mpman|, \path|manfig|, etc.
  tex/              \path|texbook.tex|, \citetitle{A Gentle Introduction to \TeX{}}, etc.
  web/              \path|webman|, \path|cwebman|
\end{tdsSummary}


\newpage
\appendix

\section{Unspecified pieces}

The \abbr{TDS} cannot address the following aspects of a functioning
\TeX{} system:

\begin{enumerate}

\item The location of executable programs: this is too site-dependent
even to recommend a location, let alone require one. A site may place
executables outside the \texmf{} tree altogether (e.g.,
\path|/usr/local/bin|), in a platform-dependent directory within
\texmf{}, or elsewhere.

\item Upgrading packages when new releases are made: we could find no
way of introducing version specifiers into \texmf{} that would do more
good than harm, or that would be practical for even a plurality of
installations.

\item The location of implementation-specific files (e.g., \TeX{}
\path|.fmt| files): by their nature, these must be left to the
implementor or \TeX{} maintainer. See Section~\ref{sec:Example
implementation-specific trees}.

\item Precisely when a package or file should be considered ``local'',
and where such local files are installed.  See Section~\ref{sec:Local
additions} for more discussion.

\end{enumerate}


\subsection{Portable filenames}
\label{sec:Portable filenames}

The \abbr{TDS} cannot require any particular restriction on filenames in
the tree, since the names of many existing \TeX{} files conform to no
standard scheme. For the benefit of people who wish to make a portable
\TeX{} distribution or installation, however, we outline here the
necessary restrictions. The \abbr{TDS} specifications themselves are
compatible with these.

\abbr{ISO}-9660 is the only universally acceptable file system format
for \abbr{CD-ROM}s.  A subset thereof meets the stringent limitations of
all operating systems in use today. It specifies the following:

\begin{itemize-squeeze}

\item File and directory names, not including any directory path or
extension part, may not exceed eight characters.

\item Filenames may have a single extension.  Extensions may not exceed
three characters. Directory names may not have an extension.

\item Names and extensions may consist of \emphasis{only} the characters
\literal{A}--\literal{Z}, \literal{0}--\literal{9}, and underscore.
Lowercase letters are excluded.

\item A period separates the filename from the extension and is always
present, even if the name or extension is missing (e.g.,
\path|FILENAME.| or \path|.EXT|).

\item A version number, ranging from 1--32767, is appended to the file
extension, separated by a semicolon (e.g., \path|FILENAME.EXT;1|).

\item Only eight directory levels are allowed, including the top-level
(mounted) directory (see Section~\ref{sec:Rooting the tree}).  Thus, the
deepest valid \abbr{ISO}-9660 path is:
\begin{ttdisplay}
texmf/L2/L3/L4/L5/L6/L7/L8/FOO.BAR;1
1     2  3  4  5  6  7  8
\end{ttdisplay}
The deepest \abbr{TDS} path needs only seven levels:
\begin{ttdisplay}
texmf/fonts/pk/cx/public/cm/dpi300/cmr10.pk
1     2     3  4  5      6  7
\end{ttdisplay}

\end{itemize-squeeze}

Some systems display a modified format of \abbr{ISO}-9660 names,
mapping alphabetic characters to lowercase, removing version numbers and
trailing periods, etc.

Before the December 1996 release, \LaTeX{} used mixed-case names for
font descriptor files.  Fortunately, it never relied on case alone to
distinguish among the files.  Nowadays, it uses only monocase names.

\section{Implementation issues}

We believe that the \abbr{TDS} can bring a great deal of order to the
current anarchic state of many \TeX{} installations.  In addition, by
providing a common frame of reference, it will ease the burden of
documenting administrative tasks.  Finally, it is a necessary part of
any reasonable system of true ``drop-in'' distribution packages for
\TeX{}.


\subsection{Adoption of the \abbr{TDS}}

[This section is retained for historical purposes; the \abbr{TDS}
is now quite firmly entrenched in most \TeX{} distributions.]

We recognize that adoption of the \abbr{TDS} will not be immediate or
universal.  Most \TeX{} administrators will not be inclined to make the
final switch until:

\begin{itemize-squeeze}
\item Clear and demonstrable benefits can be shown for the \abbr{TDS}.
\item \abbr{TDS}-compliant versions of all key programs are available
in ported, well-tested forms.
\item A ``settling'' period has taken place, to flush out problems.  The
public release of the first draft of this document was the first step in
this process.
\end{itemize-squeeze}

Consequently, most of the first trials of the \abbr{TDS} will be made by
members of the \abbr{TDS} committee and/or developers of \TeX{}-related
software.  This has already taken place during the course of our
deliberations (see Appendix~\ref{sec:Related references} for a sample
tree available electronically).  They will certainly result in the
production of a substantial number of \abbr{TDS}-compliant packages.
Indeed, the \application{te\TeX{}} and \application{\TeX{} Live}
distributions are \abbr{TDS}-compliant and in use now at many sites.

Once installable forms of key \abbr{TDS}-compliant packages are more
widespread, some \TeX{} administrators will set up \abbr{TDS}-compliant
trees, possibly in parallel to existing production directories.  This
testing will likely flush out problems that were not obvious in the
confined settings of the developers' sites; for example, it should help
to resolve system and package dependencies, package interdependencies, and
other details not addressed by this \abbr{TDS} version.

After most of the dust has settled, hopefully even conservative \TeX{}
administrators will begin to adopt the \abbr{TDS}.  Eventually, most
\TeX{} sites will have adopted the common structure, and most packages
will be readily available in \abbr{TDS}-compliant form.

We believe that this process will occur relatively quickly.  The
\abbr{TDS} committee spans a wide range of interests in the \TeX{}
community.  Consequently, we believe that most of the key issues
involved in defining a workable \abbr{TDS} definition have been covered,
often in detail.  \TeX{} developers have been consulted about
implementation issues, and have been trying out the \abbr{TDS}
arrangement.  Thus, we hope for few surprises as implementations mature.

Finally, there are several (current or prospective) publishers of \TeX{}
\abbr{CD-ROM}s.  These publishers are highly motivated to work out
details of \abbr{TDS} implementation, and their products will provide
inexpensive and convenient ways for experimentally-minded \TeX{}
administrators to experiment with the \abbr{TDS}.


\subsection{More on subdirectory searching}
\label{sec:More on subdirectory searching}

Recursive subdirectory searching is the ability to specify a search not
only of a specified directory \replaceable{d}, but recursively of all
directories below \replaceable{d}.

Since the \abbr{TDS} specifies precise locations for most files, with no
extra levels of subdirectories allowed, true recursive searching is not
actually required for a \abbr{TDS}-compliant implementation. We do,
however, strongly recommend recursive searching as the most
user-friendly and natural approach to the problem, rather than
convoluted methods to specify paths without recursion.

This feature is already supported by many implementations of \TeX{} and
companion utilities, for example \abbr{DECUS} \TeX{} for \abbr{VMS},
\application{Dvips(k)}, \application{em\TeX{}} (and its drivers),
\application{PubliC \TeX{}}, \application{Web2C}, \application{Xdvi(k)},
and \application{Y\&Y\TeX{}}.  The Kpathsea library is a reusable
implementation of subdirectory searching for \TeX{}, used in a number of
the above programs.

Even if your \TeX{} implementation does not directly support
subdirectory searching, you may find it useful to adopt the structure if
you do not use many fonts or packages. For instance, if you only use
Computer Modern and \abbr{ams} fonts, it would be feasible to store them
in the \abbr{TDS} layout and list the directories individually in
configuration files or environment variables.

The \abbr{TWG} recognizes that subdirectory searching places an extra
burden on the system and may be the source of performance bottlenecks,
particularly on slower machines.  Nevertheless, we feel that
subdirectory searching is imperative for a well-organized \abbr{TDS},
for the reasons stated in Section~\ref{sec:Subdirectory searching}.
Implementors are encouraged to provide enhancements to the basic
principle of subdirectory searching to avoid performance problems, e.g.,
the use of a filename cache (this can be as simple as a recursive
directory listing) that is consulted before disk searching begins.  If a
match is found in the database, subdirectory searching is not required,
and performance is thus independent of the number of subdirectories
present on the system.

Different implementations specify subdirectory searching differently.
In the interest of typographic clarity, the examples here do not use the
\replaceable{replaceable} font.

\begin{description-squeeze}

\item[\application{Dvips}:] via a separate
\systemitem{ENVIRONVAR}{TEXFONTS\_SUBDIR} environment variable.

\item[\application{em\TeX{}}:] \path|t:\subdir!!|; \path|t:\subdir!| for
a single level of searching.

\item[\application{Kpathsea}:] \path|texmf/subdir//|

\item[\abbr{VMS}:] \path|texmf:[subdir...]|

\item[\application{Xdvi} (patchlevel 20):] \path|texmf/subdir/**|;
\path|texmf/subdir/*| for a single level of searching.  Version 20.50
and above support the \path|//| notation.

\item[\application{Y\&Y \TeX{}}:] \path|t:/subdir//| or
\path|t:\subdir\\|.

\end{description-squeeze}


\subsection{Example implementation-specific trees}
\label{sec:Example implementation-specific trees}

The \abbr{TDS} cannot specify a precise location for
implementation-specific files, such as \path|texmf/ini|, because a site
may have multiple \TeX{} implementations.

Nevertheless, for informative purposes, we provide here the default
locations for some implementations. Please contact us with additions or
corrections. These paths are not definitive, may not match anything at
your site, and may change without warning.

We recommend all implementations have default search paths that start
with the current directory (e.g., `\path|.|').  Allowing users to
include the parent directory (e.g., `\path|..|') is also helpful.


\subsubsection{AmiWeb2c 2.0}

(Email \email|scherer@physik.rwth-aachen.de| to contact the maintainer
of this implementation.)

AmiWeb2c 2 is compatible with Web2c 7 to the greatest possible
extent, so only the very few differences are described in this
section.  Detailed information about the basic concepts is given in
the section for Web2c 7 below.

Thanks to the \path|SELFAUTO| mechanism of Kpathsea 3.0 no specific
location for the installation of AmiWeb2c is required as long as the
general structure of the distribution is preserved.

In addition to Kpathsea's \path|//| notation recursive path search may
also be started by \replaceable{DEVICE}\path|:/|, e.g., \path|TeXMF:/|
will scan this specific device completely.

Binaries coming with the AmiWeb2c distribution are installed in the
directory \path|bin/amiweb2c/| outside the common \abbr{TDS} tree
\path|share/texmf/|.  In addition to the set of AmiWeb2c binaries
you will find two subdirectories \path|local/| and \path|pastex/|
with auxiliary programs.

A stripped version of the Pas\TeX{} system (used by kind permission of
Georg He\ss{}mann) is coming with AmiWeb2c, pre-installed in its own
\path|share/texmf/amiweb2c/pastex/| directory.  If you want to use
Pas\TeX{} you have to \path|assign| the name \path|TeX:| to this place.

Documentation files in AmigaGuide format should be stored at
\path|doc/guide/| similar to \path|doc/info/|.


\subsubsection{Public \abbr{DECUS} \TeX{}}

If another \abbr{VMS} implementation besides Public \abbr{DECUS} \TeX{}
appears, the top level implementation directory name will be modified to
something more specific (e.g., \path|vms_decus|).

\begin{tdsSummary}
  texmf/
  . vms/            \abbr{VMS} implementation specific files
  . . exe/          end-user commands
  . . . common/     command procedures, command definition files, etc.
  . . . axp/        binary executables for Alpha \abbr{AXP}
  . . . vax/        binary executables for \abbr{VAX}
  . . formats/      pool files, formats, bases
  . . help/         \abbr{VMS} help library, and miscellaneous help sources
  . . mgr/          command procedures, programs, docs, etc., for system management
\end{tdsSummary}


\subsubsection{Web2c 7}

All implementation-dependent \TeX{} system files (\path|.pool|,
\path|.fmt|, \path|.base|, \path|.mem|) are stored by default directly
in \path|texmf/web2c|.  The configuration file \path|texmf.cnf| and
various subsidiary \path|MakeTeX...| scripts used as subroutines are
also stored there.

Non-\TeX{} specific files are stored following the \abbr{GNU} coding
standards.  Given a root directory \replaceable{prefix}
(\path|/usr/local| by default), we have default locations as follows:

\begin{tdsSummary}
  <prefix>/         installation root (\path|/usr/local| by default)
  . bin/            executables
  . man/            man pages
  . info/           info files
  . lib/            libraries (\path|libkpathsea.*|)
  . share/          architecture-independent files
  . . texmf/        \abbr{TDS} root
  . . . web2c/      implementation-dependent files (\path|.pool|, \path|.fmt|, \path|texmf.cnf|, etc.)
\end{tdsSummary}

See \url|http://www.gnu.org/prep/standards_toc.html| for the
rationale behind and descriptions of this arrangement. A site may of
course override these defaults; for example, it may put everything under
a single directory such as \path|/usr/local/texmf|.


\section{Is there a better way?}

Defining the \abbr{TDS} required many compromises.  Both the overall
structure and the details of the individual directories were arrived at
by finding common ground among many opinions.  The driving forces were
feasibility (in terms of what could technically be done and what could
reasonably be expected from developers) and regularity (files grouped
together in an arrangement that ``made sense'').

Some interesting ideas could not be applied due to implementations
lacking the necessary support:

\begin{itemize}

\item Path searching control at the \TeX{} level. If documents could
restrict subdirectory searching to a subdirectory via some portable
syntax in file names, restrictions on uniqueness of filenames could be
relaxed considerably (with the cooperation of the formats), and the
\TeX{} search path would not need to depend on the format.

\item Multiple logical \texmf{} trees. For example, a site might have
one (read-only) location for stable files, and a different (writable)
location for dynamically-created fonts or other files. It would be
reasonable for two such trees to be logically merged when searching.
See Michael Downes' article in the references for how this can work in
practice with Web2C.

\end{itemize}

\subsection{Macro structure}

The \abbr{TWG} settled on the
\replaceable{format}\path|/|\replaceable{package} arrangement after long
discussion about how best to arrange the files.

The primary alternative to this arrangement was a scheme which reversed
the order of these directories:
\replaceable{package}\path|/|\replaceable{format}.  This reversed
arrangement has a strong appeal: it keeps all of the files related to a
particular package in a single place.  The arrangement actually adopted
tends to spread files out into two or three places (macros,
documentation, and fonts, for example, are spread into different
sections of the tree right at the top level).

Nevertheless, the \replaceable{format}\path|/|\replaceable{package}
structure won for a couple of reasons:

\begin{itemize-squeeze}
\item It is closer to current practice; in fact, several members of the
\abbr{TWG} have already implemented the \abbr{TDS} hierarchy.  The
alternative is not in use at any known site, and the \abbr{TWG} felt it
wrong to mandate something with which there is no practical experience.

\item The alternative arrangement increases the number of top-level
directories, so the files that must be found using subdirectory
searching are spread out in a wide, shallow tree.  This could have a
profound impact on the efficiency of subdirectory searching.

\end{itemize-squeeze}


\subsection{Font structure}

The \abbr{TWG} struggled more with the font directory structure than
anything else. This is not surprising; the need to use the proliferation
of PostScript fonts with \TeX{} is what made the previous arrangement
with all files in a single directory untenable, and therefore what
initiated the \abbr{TDS} effort.


\subsubsection{Font file type location}

We considered the supplier-first arrangement in use at many sites:

\begin{ttdisplay}
texmf/fonts/\replaceable{supplier}/\replaceable{typeface}/\replaceable{type}/
\end{ttdisplay}

This improves the maintainability of the font tree, since all files
comprising a given typeface are in one place, but unless all the
programs that search this tree employ some form of caching, there are
serious performance concerns.  For example, in order to find a
\path|TFM| file, the simplest implementation would require \TeX{} to
search through all the directories that contain \abbr{PK} files in all
modes and at all resolutions.

In the end, a poll of developers revealed considerable resistance to
implementing sufficient caching mechanisms, so this arrangement was
abandoned.  The \abbr{TDS} arrangement allows the search tree to be
restricted to the correct type of file, at least.  Concerns about
efficiency remain, but there seems to be no more we can do without
abandoning subdirectory searching entirely.

We also considered segregating all font-related files strictly by file
type, so that \MF{} sources would be in a directory
\path|texmf/fonts/mf|, property list files in \path|texmf/fonts/pl|, the
various forms of Type~1 fonts separated, and so on. Although more
blindly consistent, we felt that the drawback of more complicated path
constructions outweighed this. The \abbr{TDS} merges file types
(\path|mf| and \path|pl| under \path|source|, \path|pfa| and \path|pfb|
and \path|gsf| under \path|type1|) where we felt this was beneficial.


\subsubsection{Mode and resolution location}

We considered having the \path|mode| at the bottom of the font tree:
\begin{ttdisplay}
texmf/fonts/pk/\replaceable{supplier}/\replaceable{typeface}/\replaceable{mode}/\replaceable{dpi}/
\end{ttdisplay}

In this case, however, it is difficult to limit subdirectory searching
to the mode required for a particular device.

We then considered moving the \path|dpi|\replaceable{nnn} up to below
the mode:
\begin{ttdisplay}
texmf/fonts/pk/\replaceable{mode}/\replaceable{dpi}/\replaceable{supplier}/\replaceable{typeface}/
\end{ttdisplay}

But then it is not feasible to omit the \path|dpi|\replaceable{nnn}
level altogether on systems which can and do choose to use long
filenames.


\subsubsection{Modeless bitmaps}

The \abbr{TDS} specifies using a single directory \path|modeless/| as
the mode name for those utilities which generate bitmaps, e.g.,
\path|texmf/fonts/modeless/times/|.  This has the considerable advantage
of not requiring each such directory name to be listed in a search path.

An alternative was to use the utility name below which all such
directories could be gathered.  That has the advantage of separating,
say, \path|gsftopk|-generated bitmaps from \path|ps2pk|-generated ones.
However, we decided this was not necessary; most sites will use only one
program for the purpose.  Also, \abbr{PK} and \abbr{GF} fonts generally
identify their creator in the font comment following the \path|PK_ID|
byte.

We are making an implicit assumption that \MF{} is the only program
producing mode-dependent bitmaps. If this becomes false we could add an
abbreviation for the program to mode names, as in \path|mfcx| vs.\
\path|xyzcx| for a hypothetical program \application{Xyz}, or we could
at that time add an additional program name level uniformly to the tree.
It seemed more important to concisely represent the current situation
than to worry about hypothetical possibilities that may never~happen.


\subsection{Documentation structure}

We considered placing additional documentation files in the same
directory as the source files for the packages, but we felt that users
should be able to find documentation separately from sources, since most
users have no interest in sources.

We hope that a separate, but parallel, structure for documentation would
(1)~keep the documentation together and (2)~make it as straightforward
as possible for users to find the particular documentation they were
after.


\section{Related references}
\label{sec:Related references}

This appendix gives pointers to related files and other documents.  For
\abbr{CTAN} references, we use \path|http://www.ctan.org| as the
top-level domain only to make the links be live in this document.  See
\url|http://www.ctan.org/tex-archive/CTAN.sites| for a complete list of
\abbr{ctan} sites; there are mirrors worldwide.

\begin{itemize-squeeze}

\item This document, in many formats (tex, dvi, info, pdf):\\ \hspace*{1em}
\url|http://tug.org/tds/|

\item The \abbr{TDS} mailing list archives:\\ \hspace*{1em}
\url|http://tug.org/mail-archives/twg-tds/|

\item The level~0 \abbr{DVI} driver standard:\\ \hspace*{1em}
\url|http://www.ctan.org/tex-archive/dviware/driv-standard/level-0/|

\item \citetitle{Filenames for \TeX{} fonts}, with lists of recommended
supplier and typeface names:\\ \hspace*{1em}
\url|http://tug.org/fontname/|

\item \abbr{ISO}-9660 \abbr{CD-ROM} file system standard:\\ \hspace*{1em}
\url|http://www.iso.ch/cate/cat.html|

\item \citetitle{Components of \TeX{}}, a paper by Joachim
Schrod:\\ \hspace*{1em}
\url|http://www.ctan.org/tex-archive/documentation/components-of-TeX/|

\item \citetitle{Managing Multiple TDS trees}, an article by Michael
Downes:\\ \hspace*{1em}
\url|http://tug.org/TUGboat/Articles/tb22-3/tb72downes.pdf|

\item A complete set of \MF{} modes:\\ \hspace*{1em}
\url|http://www.ctan.org/tex-archive/fonts/modes/modes.mf|

\item A large collection of \BibTeX{} databases and styles:\\ \hspace*{1em}
\url|ftp://ftp.math.utah.edu/pub/tex/bib/|

\end{itemize-squeeze}


\section{Contributors}

The \abbr{TWG} has had no physical meetings; electronic mail was the
communication medium.

Sebastian Rahtz is the \TeX{} Users Group Technical Council liaison.
Norman Walsh was the original committee chair.  Karl Berry is the
current editor.

The list of contributors has grown too large to fairly include, as some
would surely be inadvertently omitted.  Please consider the archives of
the \email|tds@tug.org| and \email|tex-live@tug.org| mailing lists as
the record of contributions.


\end{document}