.Open Standardized Generalized Mark Up Language - SGML
SGML stands for the Standardized General Markup Language.  It is the
result of generalizing and then standardizing a number of Rich
Text Formats(RTF) developed for word processing software on personal
computers.

SGML is actually a metalanguage used to define mark up languages.  The
definitions are called Document Type Definitions or DTDs.

The key notation is that of a structural tag.  Each part of a document
(an $element)
has its purpose, its place in the whole, and possibly its format, indicated by certain
tags.  Tags have two forms:
.As_is 		<name attributes>
.As_is		</name>
The first is used to start an $element of type `name`
The second form terminates the element. 
Either of these may be optional, or
both may be required.  SGML DTDs define the tags and whether the
initial and final formas are required or optional.  Further SGML DTDs
define what elements can appear inside each type of element.

These DTDs also define the various abbreviations that are permitted.
These tend to make the document easier to write and harder to
read.

The key idea is that a document has a tree structure and the tags define
the nodes in the tree.  For example a Tree with a node type A with two
parts of type B and C respectively might be encoded as:
.As_is 		<A> <B> content of B </B>  <C> content of C </C> </A>

The $attributes in the first tag of an element can be used to
further describe the meaning of the element.  For example a tag
with name IMAGE might mean that a grphic is to be included in the
text and an attribute can supply the name of the file that holds
the code forthe graphic.

SGML also defines certain elements - symbolic forms for particluar
characters in the defined type of document.

. Note
O(_)::=`Optional (_)`
# ::=`any number including none`.
non::=`anyhing but one of the following`.
. Syntax
SGML::=following
.Net
special_chars::= $nl | $np | $lt,
nl::="<nl>".
np::= "<np>".
lt::="<lt>".
encoding::= $whitspace+>$ignored | $nl+>$eoln | $np+>$new_paragraph | $lt +> less_than |+> $Id.

text::= #( $comment | $tag  |  |[ c:$commands ] ( $attributed(c) $text $negative(c) )|$normal_stuff).

normal_stuff::=#($non($commands|$tags) | $special_chars). 

tag::@$commands, -- some commands have an optional terminator
comment::="<--" #$non(">") "-->".
attributed_commands::= "<" $basic_commands #$attribute ">",
basic_commands::=($style | $character_set | $format ),
negative_commands="</" $basic_commands ">",
negative::$basic_commands->$negative_commands= "</" ! (rest).
	|- negative in $basic_commands---$negative_commands.
Example.  if "<alpha>" is a basic_command then "</alpha>" is
the associated negative tag.

attributed::$basic_commands->@$attribute_commands= "<" ! (front(rest)) ! #$attributes ">".

attribute::=$identifier $O("=" $value).
.Close.Net

. SGML and HTML
.See http://www/dick/samples/comp.html.syntax.html

. Document Type Descriptions
SGML defines a special metalanguage for describing elements
and attributes.  A document that follows these rules is said to be
a
DTD::=`Document Type Description".

DTDs can be quite complex.  One solution to this is the eXtendable
mark up Language [$XML below].

The syntax for defining an element is as follows:
element_description::= "<!ELEMENT" $command_optional $negative_optional $structure O($element_comment) ">".

element_comment::= "--" ... "--".

command_optional::= $mandatory | $optional.
negative_optional::= $mandatory | $optional.
	mandatory::="-",
	optional::="o".

structure::= "EMPTY" | O($sign) "(" $alternative #( "|" $alternative ")" | $element_name | $symbolic_element.
$alternative ::= $part | $alternative "," $part.
part::= $one_or_more | $zero_or_more | $one_part.
one_or_more::= $one_part "+".
zero_or_more::= $one_part "*".
sign::= "+" | "-".
one_part::= $structure
symbolic_element::= "%" $name ";".
element_name::=$tag.

. Attribute lists
Each elemnt has a list of possible attribute forms:
attribute_list_description::= "<!ATTLIST" $attribute_name $attribute_list ">".
attribute_list::=$variable_name $type $O("#IMPLIED")

More $TBA
...

. Glossary
TBA::="To Be Announced".
Id::=`Identity $FUNCTIONS, functions that returns a copy of its argument`, Id= fun[x]x.
FUNCTIONS::=http://www.csci.csusb.edu/dick/samples/math.syntax.html#Functions and maps.
. DocBook
DocBook is an SGML standard developed for documenting software. See
the definitive guide on paper is
.See [WalshMuelner99]
but some links to WWW sources are needed here:
.Hole

. XML
XML is the Extendable Markup Language.  It is a simplified
subset of SGML.  In particular XML documents have case sensitive
tags, attributes must be in quotes, and there are none of the
abbreviations that make SGML difficult to parse and worse to read.
See
.See http://www/dick/samples/xml.html
and
.See http://www.w3.org/XML/
MathML::=Math Markup Lanuage. Defined using $XML.
.See http://www.w3.org/Math/
OTP::="Open Trading Protocol", defined in $XML
.See http://www.otp.org
XML/EDI::=http://www.xmledi.com
ANSI X.12 group working on expressing Electronic Data Interchange standards
using $XML tags.
Rosettanet::=http://www.rosettanet.org,
--PC Industry products in $XML.
OBI::=Open Buying through the Internet,
.See http://www.openbuy.org
-- for large scale corporate procurement
ICE::=Information and Content Interchange,
.See http://www.w3.org/TR/1998/NOTE-ice-19981026
OFX::=Open Financial eXchange, for bill paying and things like that --
.See http://www.ofx.net
.Close Standardized Generalized Mark Up Language - SGML