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Standard Generalized Markup Language (SGML) marks up document logical structure in a layout-independent manner [Gol90][HPR92][Org90][SGM86]. A Document Type Definition (DTD) is used to encapsulate the logical structure of specific classes of documents. Thus, SGML provides a notation for describing classes of structured documents and for coding documents belonging to described classes. An advantage of SGML and other grammar-based document representations is the ability to perform multiple applications on a single document source file. The International Committee on Accessible Documents (ICAD) has been working on defining an accessible DTD[+], but at present their work does not encompass mathematical content.

Though SGML is now used to markup a variety of documents by
many government agencies, it still has very little support for
marking up technical content, *e.g.,* mathematics. There
is ongoing work to remedy this situation. In the last year, the
SGML-Math committee has been working on a math DTD for SGML.
This work is not yet complete, but it has raised a few
interesting issues. The main point of discussion has been
whether it is possible to design a math DTD that captures
semantic information about the mathematical constructs being
marked up. Though it would be nice to have all of a
mathematical construct's semantic content when processing the
document, *e.g.,* in our case producing audio
renderings, this seems almost unattainable. There is as yet no
firm agreement on this point, but the trend seems to be to move
towards a math DTD that captures the layout as embodied by TeX.
Defining a DTD that captures full mathematical semantics would
make it difficult to invent new notation. TeX, by only
capturing the layout constructs used to build up written
mathematics, side-steps this issue, and the resulting system
makes it easy to invent new notation. However, this also makes
recognition more difficult. Some of the problems present in
La)TeX are being addressed by ongoing work on the project.

Significant work has been carried out in the context of
structure-sensitive editors for documents. This work has
focused on the design of appropriate document encodings that
capture high-level structure unambiguously. Another topic of
interest has been the capture of hypertext links within the
context of structured documents. The logical structure of
documents is typically captured using a tree-like
representation consisting of hierarchical units. The challenge
of integrating this model with the notion of hypertext links
has been successfully addressed by the design of HyperText
Markup Language (HTML), an SGML-based markup system for
encoding structured hypertext documents. Finally, the aim of
achieving the best of two worlds, *i.e.,* the power
afforded by a grammar-based markup system and the
user-interface provided by WYSIWYG systems (what you see is
what you get) has led to work on providing multiple
synchronized views of a document [Har88]. See [Bro88][QNA90][PS88][Ver90][BG90][CJ90][KS84][Ass86][Kat87][FS89][SFR92][Lev88][FBN<6287>>+90][SF90][SF88][PI88][KLMN90][BB90][LG90][QV92] for details on relevant
work in this area.

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TV Raman

Thu Mar 9 20:10:41 EST 1995