namespace lemon {
/*!


\page lemon_file_format LEMON Graph File Format

The standard graph IO enables one to store graphs and additional maps
(i.e. functions on the nodes or edges) in a flexible and efficient way. 
Before you read this page you should be familiar with LEMON 
\ref graphs "graphs" and \ref maps-page "maps".

\section format The general file format

The file contains sections in the following order:

\li nodeset
\li edgeset
\li nodes
\li edges
\li attributes

Some of these sections can be omitted, but you will basicly need the nodeset
section (unless your graph has no nodes at all) and the edgeset section
(unless your graph has no edges at all). 

The nodeset section describes the nodes of your graph: it identifies the nodes
and gives the maps defined on them, if any. It starts with the
following line:

<tt>\@nodeset</tt>

The next line contains the names of the nodemaps, separated by whitespaces.  Each
following line describes a node in the graph: it contains the values of the
maps in the right order. The map named "label" should contain unique values
because it is regarded as a label map. These labels need not be numbers but they
must identify the nodes uniquely for later reference. For example:

\code
@nodeset
label  x-coord  y-coord  color
3   1.0      4.0      blue
5   2.3      5.7      red
12  7.8      2.3      green
\endcode

The edgeset section is very similar to the nodeset section, it has
the same coloumn oriented structure. It starts with the line 

<tt>\@edgeset</tt>

The next line contains the whitespace separated list of names of the edge
maps.  Each of the next lines describes one edge. The first two elements in
the line are the labels of the source and target (or tail and head) nodes of the
edge as they occur in the label node map of the nodeset section. You can also
have an optional label map on the edges for later reference (which has to be
unique in this case).

\code
@edgeset
             label      weight   note
3   5        a          4.3      a-edge
5   12       c          2.6      c-edge
3   12       g          3.4      g-edge
\endcode

The \e nodes section contains <em>labeled (distinguished) nodes</em> 
(i.e. nodes having a special
label on them). The section starts with

<tt> \@nodes </tt>

Each of the next lines contains a label for a node in the graph 
and then the label as described in the \e nodeset section.

\code
@nodes 
source 3
target 12
\endcode

The last section describes the <em>labeled (distinguished) edges</em>
(i.e. edges having a special label on them). It starts with \c \@edges
and then each line contains the name of the edge and the label.

\code
@edges 
observed c
\endcode


The file may contain empty lines and comment lines. The comment lines
start with an \c # character.

The attributes section can handle some information about the graph. It
contains key-value pairs in each line (a key and the mapped value to key). The
key should be a string without whitespaces, the value can be of various types.

\code
@attributes
title "Four colored planar graph"
author "Balazs DEZSO"
copyright "Lemon Library"
version 12
\endcode

Finally, the file should be closed with \c \@end line.


\section use Using graph input-output


The graph input and output is based on <em> reading and writing
commands</em>. The user gives reading and writing commands to the reader or
writer class, then he calls the \c run() method that executes all the given
commands.

\subsection write Writing a graph

The \ref lemon::GraphWriter "GraphWriter" template class
provides the graph output. To write a graph
you should first give writing commands to the writer. You can declare
writing command as \c NodeMap or \c EdgeMap writing and labeled Node and
Edge writing.

\code
GraphWriter<ListGraph> writer(std::cout, graph);
\endcode

The \ref lemon::GraphWriter::writeNodeMap() "writeNodeMap()"
function declares a \c NodeMap writing command in the
\ref lemon::GraphWriter "GraphWriter".
You should give a name to the map and the map
object as parameters. The NodeMap writing command with name "label" should write a 
unique map because it will be regarded as a label map.

\see IdMap, DescriptorMap  

\code
IdMap<ListGraph, Node> nodeLabelMap;
writer.writeNodeMap("label", nodeLabelMap);

writer.writeNodeMap("x-coord", xCoordMap);
writer.writeNodeMap("y-coord", yCoordMap);
writer.writeNodeMap("color", colorMap);
\endcode

With the \ref lemon::GraphWriter::writeEdgeMap() "writeEdgeMap()"
member function you can give an edge map
writing command similar to the NodeMaps.

\see IdMap, DescriptorMap  

\code
DescriptorMap<ListGraph, Edge, ListGraph::EdgeMap<int> > edgeDescMap(graph);
writer.writeEdgeMap("descriptor", edgeDescMap);

writer.writeEdgeMap("weight", weightMap);
writer.writeEdgeMap("note", noteMap);
\endcode

With \ref lemon::GraphWriter::writeNode() "writeNode()"
and \ref lemon::GraphWriter::writeEdge() "writeEdge()"
functions you can designate Nodes and
Edges in the graph. For example, you can write out the source and target node
of a maximum flow instance.

\code
writer.writeNode("source", sourceNode);
writer.writeNode("target", targetNode);

writer.writeEdge("observed", edge);
\endcode

With \ref lemon::GraphWriter::writeAttribute() "writeAttribute()"
function you can write an attribute to the file.

\code
writer.writeAttribute("author", "Balazs DEZSO");
writer.writeAttribute("version", 12);
\endcode

After you give all write commands you must call the
\ref lemon::GraphWriter::run() "run()" member
function, which executes all the writing commands.

\code
writer.run();
\endcode

\subsection reading Reading a graph

The file to be read may contain several maps and labeled nodes or edges.
If you read a graph you need not read all the maps and items just those
that you need. The interface of the \ref lemon::GraphReader "GraphReader"
is very similar to
the \ref lemon::GraphWriter "GraphWriter"
but the reading method does not depend on the order of the
given commands.

The reader object assumes that each not read value does not contain 
whitespaces, therefore it has some extra possibilities to control how
it should skip the values when the string representation contains spaces.

\code
GraphReader<ListGraph> reader(std::cin, graph);
\endcode

The \ref lemon::GraphReader::readNodeMap() "readNodeMap()"
function reads a map from the \c nodeset section.
If there is a map that you do not want to read from the file and there are
whitespaces in the string represenation of the values then you should
call the \ref lemon::GraphReader::skipNodeMap() "skipNodeMap()"
template member function with proper parameters.

\see QuotedStringReader

\code
reader.readNodeMap("x-coord", xCoordMap);
reader.readNodeMap("y-coord", yCoordMap);

reader.readNodeMap<QuotedStringReader>("label", labelMap);
reader.skipNodeMap<QuotedStringReader>("description");

reader.readNodeMap("color", colorMap);
\endcode

With the \ref lemon::GraphReader::readEdgeMap() "readEdgeMap()"
member function you can give an edge map
reading command similar to the NodeMaps. 

\code
reader.readEdgeMap("weight", weightMap);
reader.readEdgeMap("label", labelMap);
\endcode

With \ref lemon::GraphReader::readNode() "readNode()"
and \ref lemon::GraphReader::readEdge() "readEdge()"
functions you can read labeled Nodes and
Edges.

\code
reader.readNode("source", sourceNode);
reader.readNode("target", targetNode);

reader.readEdge("observed", edge);
\endcode

With \ref lemon::GraphReader::readAttribute() "readAttribute()"
function you can read an attribute from the file.

\code
std::string author;
writer.readAttribute("author", author);
int version;
writer.writeAttribute("version", version);
\endcode

After you give all read commands you must call the
\ref lemon::GraphReader::run() "run()" member
function, which executes all the commands.

\code
reader.run();
\endcode

If you want to lear more, read the \ref read_write_bg "background technics".

\author Balazs Dezso
*/
}