Trivial Graph Format

Trivial Graph Format (TGF) is a very simple text-based file format for describing graphs. It consists of a list of node definitions, which map node IDs to labels, followed by a list of edges, which specify node pairs and an optional edge label. Node IDs can be arbitrary identifiers, whereas labels for both nodes and edges are plain strings.

The graph may be interpreted as a directed or undirected graph. For directed graphs, to specify the concept of bidirectionality in an edge, one may either specify two edges (forward and back), or differentiate the edge by means of a label. For more powerful specification of graphs, see the other graph file formats below.

Example

A simple graph with 2 nodes and 1 edge might look like this:

1 First node
2 Second node
#
1 2 Edge between the two

Ease of use

TGF is useful for easily importing arbitrary data into a graph manipulation tool such as yEd. Because of the simplicity of the format, it is straightforward to use small programs or scripts to convert domain-specific data to this general format. For example, given a Makefile like this:

myprogram: myprogram.o libmytools.so
    gcc -L. -lmylib -o $@ $<

myprogram.o: myprogram.c
    gcc -c -o $@ $<

libmytools.so: mytools1.o mytools2.o
    gcc -shared -o $@ $<

mytools1.o: mytools1.c
    gcc -c -o $@ $<

mytools2.o: mytools2.c
    gcc -c -o $@ $<

clean:
    rm myprogram myprogram.o libmytools.so mytools1.o mytools2.o

It is possible to use a simple script, such as the following Python program, to turn the Makefile dependencies into TGF output:

#!/usr/bin/python

import fileinput, re

depends = {}
for line in fileinput.input():
    m = re.match('(.+):\s*(.*)',line) # find every depenency line of the form "<item>: <dependencies>"
    if m:
        item = m.group(1)
        dependency_list = m.group(2)
        print item,item # node definition
        
        if dependency_list: # there are dependencies
            depends[item] = dependency_list.split() # store the list into a dictionary for later

print "#" # end of node list, start of edge list

for item in depends:
    for dependency in depends[item]:
        print item,dependency # edge definition

This will produce a TGF graph which can then be visualized and analyzed using a graph manipulation tool. The above content yields the following graph:

Other Graph File Formats

• GraphML, a graph exchange format based on XML -- GraphML
• GXL, another graph exchange format based on XML -- GXL
• GML is another widely used graph exchange format. -- GML
• XGMML an XML-based graph markup language closely related to GML -- XGMML

See also

• yEd, a wide-spread graph editor that can handle TGF file format.

External links

• More on the file format