 
\documentstyle[12pt]{article}
  \setlength{\oddsidemargin}{0in}\setlength{\textwidth}{6.5in}
  \setlength{\topmargin}{0in}\setlength{\headheight}{0in}
  \setlength{\headsep}{0in}\addtolength{\textheight}{1.5in}
  \setlength{\parskip}{.15in}
\begin{document}
\thispagestyle{empty}
\begin{flushleft}
\vspace*{.5in}
\begin{center}
{\Large \bf TEI Syntax and Metalanguage Committee\\
\vspace*{.25in}
Exchanging Documents\\
\vspace*{.25in}
Document Number: TEI MLW24\\
\vspace*{.25in}
July17, 1990}
\vspace*{.5in}
 
\end{center}
In the TEI P1 guidelines, on page 2, the following conditions are set
out for document interchange:
\begin{enumerate}
\item adherence to the TEI SGML declaration and DTD
\item documentation for all tags not in the DTD
\item inclusion of the TEI header at the beginning of the document
\item all text must be in the given subset of the ISO 646 character encoding
\end{enumerate}
Additionally, some way should be found of ensuring that all the pieces
of the document are present. That is, all entity references are expandable
upon receipt of the document, except those that are public and are therefore
already at all sites. If a file of entity definitions is missing or if the
author forgot to include an entity definition, the document will not be
completely readable. Especially if the guidelines given in chapter 8 of
TEI P1 are followed and the number of entities is large.
 
One solution to this problem is the SGML Document Interchange Format (SDIF)
which is an ISO standard (9069) meant for this purpose. The standard calls
for a packer/unpacker pair which takes a set of one or more related documents
and marks each entity reference in them. The document package is wrapped in
some SDIF identifiers and all entity references are checked. The resulting
data stream then can be unpacked upon receipt, with a reasonable guarantee
that all entities referenced will be defined. The details of the packing and
unpacking are contained in the standard and are unimportant here.
 
Since TEI requires something like SDIF to ensure that whole documents are
interchanged, it would be nice if TEI could adopt SDIF imediately.
Unfortunately, in our investigation of this standard, we have not found an
implementation of SDIF, nor anyone who has actually used it. It seems to
meet or exceed the requirements,
but it is not really usable as yet. Perhaps if a TEI document packer is
implemented which does such things as putting the document in canonical form
and ensuring that its character coding set conforms to the ISO 646 subset,
it could also use SDIF to ensure that entity definitions are present or
part of some public set of entity definitions. Alternatively, putting the
document in a canonical form could check the entity references as well,
negating the need for SDIF. Since SDIF is not being used by, seemingly,
anyone, TEI can set its own course without risk of damaging the
universatility of its document interchange.
 
\end{flushleft}
\end{document}
 
 
