1 /* -*- mode: C++; indent-tabs-mode: nil; -*-
3 * This file is a part of LEMON, a generic C++ optimization library.
5 * Copyright (C) 2003-2010
6 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
7 * (Egervary Research Group on Combinatorial Optimization, EGRES).
9 * Permission to use, modify and distribute this software is granted
10 * provided that this copyright notice appears in all copies. For
11 * precise terms see the accompanying LICENSE file.
13 * This software is provided "AS IS" with no warranty of any kind,
14 * express or implied, and with no claim as to its suitability for any
21 [PAGE]sec_lgf[PAGE] Input-Output for Graphs
23 \todo Clarify this section.
25 LEMON provides a versatile file format for storing graphs
26 and related node and arc maps.
27 Such a format should be really flexible, it should be able to store arbitrary
28 number of maps of arbitrary value types.
29 On the other hand, the file size and the ease of processing are also critical
30 to support storing huge graphs, which is a major goal of LEMON.
31 These requirements forbid using complicated and deeply structured formats
33 That is why a compact file format is designed for LEMON instead of using
34 hierarchical formats, such as GraphML, GXL or GML.
36 The LEMON Graph Format (LGF) comprises different sections, for
37 example a digraph is stored in a \c @nodes and an \c @arcs
38 section. These parts use column oriented formats, each
39 column belongs to a map in the graph. The first line of the section associate
40 names to these maps, which can be used to refer them.
41 Note that this simple idea makes it possible to extend the files with
42 new maps (columns) at any
43 position without having to modify the codes using these files.
45 The \c label map has special role, it must store unique values, which in turn
47 to the nodes and arcs in the file. Finally, the first two column of the
48 \c @arcs section is anonymous, they indicate the source and target nodes,
68 caption "A shortest path problem"
71 The \ref DigraphReader and \ref DigraphWriter classes are used
72 to read and write a digraph and corresponding maps. By default, a map
73 can be used with these classes if its value type has standard I/O
74 operators (\c operator<<(ostream&, T) and \c operator>>(istream&, T&)).
75 Otherwise, a function object
76 can be specified which converts the value type to \c std::string.
77 The above LGF file can be scanned as follows.
81 ListDigraph::NodeMap<dim2::Point<int> > coord(g);
82 ListDigraph::ArcMap<int> length(g);
83 ListDigraph::Node src;
86 digraphReader(g, std::cin)
87 .nodeMap("coord", coord)
88 .arcMap("length", length)
89 .attribute("caption", title)
94 Apart from LGF, the library can also interpret other graph
95 formats, such as the well-known DIMACS format or the NAUTY graph6
100 The \e LGF is a <em>column oriented</em>
101 file format for storing graphs and associated data like
104 Each line with \c '#' first non-whitespace
105 character is considered as a comment line.
107 Otherwise the file consists of sections starting with
108 a header line. The header lines starts with an \c '@' character followed by the
109 type of section. The standard section types are \c \@nodes, \c
110 \@arcs and \c \@edges
111 and \@attributes. Each header line may also have an optional
112 \e name, which can be use to distinguish the sections of the same
115 The standard sections are column oriented, each line consists of
116 <em>token</em>s separated by whitespaces. A token can be \e plain or
117 \e quoted. A plain token is just a sequence of non-whitespace characters,
118 while a quoted token is a
119 character sequence surrounded by double quotes, and it can also
120 contain whitespaces and escape sequences.
122 The \c \@nodes section describes a set of nodes and associated
123 maps. The first is a header line, its columns are the names of the
124 maps appearing in the following lines.
125 One of the maps must be called \c
126 "label", which plays special role in the file.
128 non-empty lines until the next section describes nodes of the
129 graph. Each line contains the values of the node maps
130 associated to the current node.
134 label coordinates size title
135 1 (10,20) 10 "First node"
136 2 (80,80) 8 "Second node"
137 3 (40,10) 10 "Third node"
140 The \c \@arcs section is very similar to the \c \@nodes section,
141 it again starts with a header line describing the names of the maps,
142 but the \c "label" map is not obligatory here. The following lines
143 describe the arcs. The first two tokens of each line are
144 the source and the target node of the arc, respectively, then come the map
145 values. The source and target tokens must be node labels.
155 The \c \@edges is just a synonym of \c \@arcs. The \@arcs section can
156 also store the edge set of an undirected graph. In such case there is
157 a conventional method for store arc maps in the file, if two columns
158 has the same caption with \c '+' and \c '-' prefix, then these columns
159 can be regarded as the values of an arc map.
161 The \c \@attributes section contains key-value pairs, each line
162 consists of two tokens, an attribute name, and then an attribute
163 value. The value of the attribute could be also a label value of a
164 node or an edge, or even an edge label prefixed with \c '+' or \c '-',
165 which regards to the forward or backward directed arc of the
172 caption "LEMON test digraph"
175 The \e LGF can contain extra sections, but there is no restriction on
176 the format of such sections.