/*!

 \page graph-io-page Graph Input-Output

 The standard graph IO makes possible to store graphs and additional maps

 in flexible and efficient way. 

 \section format The general file format

 The graph file contains at most four section in the next order:

 \li nodeset

 \li edgeset

 \li nodes

 \li edges

 The nodeset section starts with the \c \@nodeset line.

 The next line contains the names of the maps separated by whitespaces.

 Each following line describes a node in the graph, it contains

 in the right order the values of the maps. The first map should contain

 unique values because it regarded as Id-map. 

 \code

 @nodeset

 id  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

 same coloumn oriented structure. It starts with the line \c \@edgeset

 The next line contains the whitespace separated list of names of the map.

 Each of the next lines describes one edge. The first two element in the line

 is the ID of the source and target node as occurs in the first node map. 

 \code

 @edgeset

              id    weight   label

 3   5        a     4.3      a-edge

 5   12       c     2.6      c-edge

 3   12       g     3.4      g-edge

 \endcode

 The next section contains outpointed nodes. The section starts with

 \c \@nodes. Each of the next lines contains a label for a node in the graph 

 and then the ID described in the first column in the nodeset.

 \code

 @nodes 

 source 3

 target 12

 \endcode

 The last section describes the outpointed edges. It starts with \c \@edges

 and then each line contains the name of the edge and the ID.

 \code

 @nodes 

 observed c

 \endcode

 The file ends with the \c \@end line.

 The file may contain empty lines and comment lines. The comment lines

 start with an \c # character.

 \code

 @end

 \endcode

 \section use Using graph input-output

 The graph input and output based on writing and reading commands. The user

 adds writing and reading commands for the reader or writer class, after 

 calls the \c run() method what executes all the given commands.

 \subsection write Writing a graph

 The \c GraphWriter class provides the graph output. To write a graph

 you should first give writing commands for the writer. You can declare

 write command as \c NodeMap or \c EdgeMap writing and outpointed Node and

 Edge writing.

 \code

 GraphWriter<ListGraph> writer(graph);

 \endcode

 The \c addNodeMap() function declares a \c NodeMap writing command in the

 \c GraphWriter. You should give as parameter the name of the map and the map

 object. The first NodeMap writing command should write an unique map because

 it is regarded as ID map.

 \see IdMap, DescriptorMap  

 \code

 IdMap<ListGraph, Node> nodeIdMap;

 writer.addNodeMap("id", nodeIdMap);

 writer.addNodeMap("x-coord", xCoordMap);

 writer.addNodeMap("y-coord", yCoordMap);

 writer.addNodeMap("color", colorMap);

 \endcode

 With the \c addEdgeMap() member function you can give an edge map

 writing command similar to the NodeMaps. The first map writing command should

 write unique map.

 \see IdMap, DescriptorMap  

 \code

 DescriptorMap<ListGraph, Edge, ListGraph::EdgeMap<int> > edgeDescMap(graph);

 writer.addEdgeMap("descriptor", edgeDescMap);

 writer.addEdgeMap("weight", weightMap);

 writer.addEdgeMap("label", labelMap);

 \endcode

 With \c addNode() and \c addEdge() functions you can point out Nodes and

 Edges in the graph. By example, you can write out the source and target

 of the graph.

 \code

 writer.addNode("source", sourceNode);

 writer.addNode("target", targetNode);

 writer.addEdge("observed", edge);

 \endcode

 After you give all write commands you must call the \c run() member

 function, what execute all the write commands.

 \code

 writer.run();

 \endcode

 \subsection reading Reading a graph

 The given file format may contain many maps and outpointed 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 \c GraphReader is very similar to

 the GraphWriter but the reading method does not depend on the order the

 given commands.

 The reader object suppose that each not readed value does not contains 

 whitespaces therefore it has some extra possibilities to control how could

 it skip the values when the string representation contains spaces.

 \code

 GraphReader<ListGraph> reader(graph);

 \endcode

 The \c addNodeMap() function reads a map from the \c \@nodeset section.

 If there is a map what you do not want to read from the file and there is

 whitespace in the string represenation of the values then you should

 call the \c skipNodeMap() template member function with proper parameters.

 \see QuotedStringReader

 \code

 reader.addNodeMap("x-coord", xCoordMap);

 reader.addNodeMap("y-coord", yCoordMap);

 reader.addNodeMap<QuotedStringReader>("label", labelMap);

 reader.skipNodeMap<QuotedStringReader>("description");

 reader.addNodeMap("color", colorMap);

 \endcode

 With the \c addEdgeMap() member function you can give an edge map

 reading command similar to the NodeMaps. 

 \code

 reader.addEdgeMap("weight", weightMap);

 reader.addEdgeMap("label", labelMap);

 \endcode

 With \c addNode() and \c addEdge() functions you can read outpointed Nodes and

 Edges.

 \code

 reader.addNode("source", sourceNode);

 reader.addNode("target", targetNode);

 reader.addEdge("observed", edge);

 \endcode

 After you give all read commands you must call the \c run() member

 function, what execute all the commands.

 \code

 reader.run();

 \endcode

 \section types The background of the Reading and Writing

 The \c GraphReader should know how can read a Value from the given map.

 By the default implementation the input operator reads a value from

 the stream and the type of the readed value is the value type of the given map.

 When the reader should skip a value in the stream, because you do not

 want to store it in map, the reader skips a character sequence without 

 whitespace. 

 If you want to change the functionality of the reader, you can use

 template parameters to specialize it. When you give a reading

 command for a map you can give a Reader type as template parameter.

 With this template parameter you can control how does read the Reader

 a value from the stream.

 The reader has the next structure: 

 \code

 struct TypeReader {

   typedef TypeName Value;

   void read(std::istream& is, Value& value);

 };

 \endcode

 By example, the \c "strings" nodemap contains strings and you do not need

 the value of the string just the length. Then you can implement own Reader

 struct.

 \code

 struct LengthReader {

   typedef int Value;

   void read(std::istream& is, Value& value) {

     std::string tmp;

     is >> tmp;

     value = tmp.length();

   }

 };

 ...

 reader.addNodeMap<LengthReader>("strings", lengthMap);

 \endcode  

 The global functionality of the reader class can be changed by giving a

 special template parameter for the GraphReader class. In default way the

 template parameter the \c DefaultReaderTraits. A reader traits class 

 should provide an inner template class Reader for each type, and an 

 DefaultReader for skipping a value.

 The specialization of the writing should be very similar to the reading.

 */