source: lemon-0.x/doc/graph_io.dox @ 1255:6455f64a85dc

namespace lemon {
/*!



\page graph-io-page Graph Input-Output

The standard graph IO makes possible to store graphs and additional maps
in a 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 elements in the line
are the ID of the source and target node as they occur 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 <em>labeles nodes</em> (i.e. nodes having a special
label on them). 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 <em>labeles 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 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, then 
calls the \c run() method that 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 labeled 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 a 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, which execute all the write commands.

\code
writer.run();
\endcode

\subsection reading Reading a graph

The given file format 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 \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 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(graph);
\endcode

The \c addNodeMap() 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 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 labeled 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, which 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. By default, the
template parameter is \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.


*/
}