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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
<!--
    This is a generated document.  Do not edit.
-->
<HTML VERSION="2.0">
<HEAD>
<TITLE>The DOT Language</TITLE>
</HEAD>
<BODY BGCOLOR=white>
<A NAME="top"></A>
<H1 ALIGN=CENTER>The DOT Language</H1>
<HR>
The following is an abstract grammar defining the DOT language.
Terminals are shown in bold font and nonterminals in italics.
Literal characters are given in single quotes.
Parentheses ( and ) indicate grouping when needed.
Square brackets [ and ] enclose optional items.
Vertical bars | separate alternatives.
<TABLE>
<TR>
  <TD ALIGN=RIGHT><I>graph</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT>[ <B>strict</B> ] (<B>graph</B> | <B>digraph</B>) [ <I>ID</I> ] <B>'{'</B> <I>stmt_list</I> <B>'}'</B></TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>stmt_list</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT>[ <I>stmt</I> [ <B>';'</B> ] [ <I>stmt_list</I> ] ]</TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>stmt</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT><I>node_stmt</I></TD>
</TR>
<TR>
  <TD ALIGN=RIGHT></TD>
  <TD ALIGN=LEFT>|</TD>
  <TD ALIGN=LEFT><I>edge_stmt</I></TD>
</TR>
<TR>
  <TD ALIGN=RIGHT></TD>
  <TD ALIGN=LEFT>|</TD>
  <TD ALIGN=LEFT><I>attr_stmt</I></TD>
</TR>
<TR>
  <TD ALIGN=RIGHT></TD>
  <TD ALIGN=LEFT>|</TD>
  <TD ALIGN=LEFT><I>ID</I> <B>'='</B> <I>ID</I></TD>
</TR>
<TR>
  <TD ALIGN=RIGHT></TD>
  <TD ALIGN=LEFT>|</TD>
  <TD ALIGN=LEFT><I>subgraph</I></TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>attr_stmt</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT>(<B>graph</B> | <B>node</B> | <B>edge</B>) <I>attr_list</I></TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>attr_list</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT><B>'['</B> [ <I>a_list</I> ] <B>']'</B> [ <I>attr_list</I> ]</TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>a_list</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT><I>ID</I> [ <B>'='</B> <I>ID</I> ] [ <B>','</B> ] [ <I>a_list</I> ]</TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>edge_stmt</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT>(<I>node_id</I> | <I>subgraph</I>) <I>edgeRHS</I> [ <I>attr_list</I> ]</TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>edgeRHS</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT><I>edgeop</I> (<I>node_id</I> | <I>subgraph</I>) [ <I>edgeRHS</I> ]</TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>node_stmt</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT><I>node_id</I> [ <I>attr_list</I> ]</TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>node_id</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT><I>ID</I> [ <I>port</I> ]</TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>port</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT><B>':'</B> <I>ID</I> [ <B>':'</B> <I>compass_pt</I> ]</TD>
</TR>
<TR>
  <TD ALIGN=RIGHT></TD>
  <TD ALIGN=LEFT>|</TD>
  <TD ALIGN=LEFT><B>':'</B> <I>compass_pt</I></TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>subgraph</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT>[ <B>subgraph</B> [ <I>ID</I> ] ] <B>'{'</B> <I>stmt_list</I> <B>'}'</B></TD>
</TR>
<TR>
  <TD ALIGN=RIGHT><I>compass_pt</I></TD>
  <TD ALIGN=LEFT>:</TD>
  <TD ALIGN=LEFT>(<B>n</B> | <B>ne</B> | <B>e</B> | <B>se</B> | <B>s</B> | <B>sw</B> | <B>w</B> | <B>nw</B> | <B>c</B> | <B>_</B>)</TD>
</TR>
</TABLE>
<P>
The keywords <B>node</B>, <B>edge</B>, <B>graph</B>, <B>digraph</B>,
<B>subgraph</B>, and <B>strict</B> are case-independent.
Note also that the allowed compass point values are not keywords, so
these strings can be used elsewhere as ordinary identifiers and, conversely,
the parser will actually accept any identifier.
<P>
An <I>ID</I> is one of the following: 
<MENU>
<LI> Any string of alphabetic (<TT>[a-zA-Z\200-\377]</TT>) characters, underscores (<TT>'_'</TT>) or
digits (<TT>[0-9]</TT>), not beginning with a digit;
<LI> a number [<tt>-</tt>]<sup>?</sup>(<tt>.</tt>[<tt>0</tt>-<tt>9</tt>]<sup>+</sup>  | [<tt>0</tt>-<tt>9</tt>]<sup>+</sup>(<tt>.</tt>[<tt>0</tt>-<tt>9</tt>]<sup>*</sup>)<sup>?</sup> ); 
<LI> any double-quoted string (&quot;...&quot;) possibly containing escaped 
quotes (\&quot;)<SUP>1</SUP>;
<LI> an <A NAME=html>HTML string</A> (&lt;...&gt;).
</MENU>
Note that in HTML strings, angle
brackets must occur in matched pairs, and unescaped newlines are allowed.
In addition, the content must be legal XML, so that the special XML
escape sequences for &quot;, &amp;, &lt;, and &gt; may be necessary
in order to embed these characters in attribute values or raw text.
<P>
Both quoted strings and HTML strings are scanned as a unit, so
any embedded comments will be treated as part of the strings.
<P>
An <I>edgeop</I> is <TT>-></TT> in directed graphs and <TT>--</TT> in
undirected graphs.
<P>
An <I>a_list</I> clause of the form <I>ID</I> is equivalent to
<I>ID</I><TT>=true</TT>.
<P>
The language supports C++-style comments: <TT>/* */</TT> and <TT>//</TT>.
In addition, a line beginning with a '#' character is considered a line
output from a C preprocessor (e.g., #  34 to indicate line 34 ) and discarded.
<P>
Semicolons aid readability but are not required except in the rare case
that a named subgraph with no body immediately preceeds an anonymous
subgraph, since the precedence rules cause this sequence to be parsed as
a subgraph with a heading and a body.
Also, any amount of whitespace may be inserted between terminals.
<P>
As another aid for readability, dot allows single logical lines to
span multiple physical lines using the standard C convention of a
backslash immediately preceding a newline character. In addition, 
double-quoted strings can be concatenated using a '+' operator.
As HTML strings can contain newline characters, they do not support the
concatenation operator.
<H2>Semantic Notes</H2>
If a default attribute is
defined using a <B>node</B>,  <B>edge</B>, or  <B>graph</B> statement,
or by an attribute assignment not attached to a node or edge, any object of the
appropriate type defined afterwards will inherit this attribute value.
This holds until the default attribute is set to a new value, from which
point the new value is used. Objects defined before a default attribute
is set will have an empty string value attached to the attribute once
the default attribute definition is made.
<P>
Note, in particular, that a subgraph receives the attribute settings of
its parent graph at the time of its definition. This can be useful; for
example, one can assign a font to the root graph and all subgraphs will
also use the font. For some attributes, however, this property is
undesirable. If one attaches a label to the root graph, it is probably
not the desired effect to have the label used by all subgraphs. Rather
than listing the graph attribute at the top of the graph, and the
resetting the attribute as needed in the subgraphs, one can simple defer
the attribute definition if the graph until the appropriate subgraphs
have been defined.
<P>
If an edge belongs to a cluster, its endpoints belong to that cluster.
Thus, where you put an edge can effect a layout, as clusters are sometimes
laid out recursively.
<H2>Character encodings</H2>
The DOT language assumes at least the ascii character set.
Quoted strings, both ordinary and HTML-like, may contain non-ascii characters.
In most cases, these strings are uninterpreted: they simply serve as
unique identifiers or values passed through untouched. Labels, however,
are meant to be displayed, which requires that the software be able to
compute the size of the text and determine the appropriate glyphs. 
For this, it needs to know what character encoding is used.
<P>
By default, DOT assumes the UTF-8 character encoding. It also accepts
the Latin1 (ISO-8859-1) character set, assuming the input graph uses
the <B><A HREF=attrs.html#a:charset>charset</A></B> attribute to 
specify this. For graphs using other
character sets, there are usually programs, such as <TT>iconv</TT>, which
will translate from one character set to another.
<P>
Another way to avoid non-ascii characters in labels is to use HTML entities
for special characters. During label evaluation, these entities are
translated into the underlying character. This
<a HREF="http://www.graphviz.org/doc/char.html">
table</a> shows the supported entities, with their Unicode value, a typical
glyph, and the HTML entity name. Thus, to include a lower-case Greek beta
into a string, one can use the ascii sequence <TT>&amp;beta;</TT>. 
In general, one should only use entities that are allowed in the output
character set, and for which there is a glyph in the font.
<HR>
<OL TYPE="1">
<LI> In quoted strings in DOT, the only escaped character is double-quote
("). That is, in quoted strings, the dyad \" is converted to "; all other
characters are left unchanged. In particular, \\ remains \\. Layout
engines may apply additional escape sequences.
</OL>
</BODY>
</HTML>