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

*/

}