Modules in this distro¶

o GraphViz

o GraphViz::No

o GraphViz::Small

o GraphViz::Regex

o GraphViz::XML

o GraphViz::Data::Grapher

o GraphViz::Parse::RecDescent

o GraphViz::Parse::Yacc

o GraphViz::Parse::Yapp

What is a graph?¶

A (undirected) graph is a collection of nodes linked together with edges.

A directed graph is the same as a graph, but the edges have a direction.

What is GraphViz?¶

This module is an interface to the GraphViz toolset (http://www.graphviz.org/). The GraphViz tools provide automatic graph layout and drawing. This module simplifies the creation of graphs and hides some of the complexity of the GraphViz module.

Laying out graphs in an aesthetically-pleasing way is a hard problem - there may be multiple ways to lay out the same graph, each with their own quirks. GraphViz luckily takes part of this hard problem and does a pretty good job in a couple of seconds for most graphs.

Why should I use this module?¶

Observation aids comprehension. That is a fancy way of expressing that popular faux-Chinese proverb: "a picture is worth a thousand words".

Text is not always the best way to represent anything and everything to do with a computer programs. Pictures and images are easier to assimilate than text. The ability to show a particular thing graphically can aid a great deal in comprehending what that thing really represents.

Diagrams are computationally efficient, because information can be indexed by location; they group related information in the same area. They also allow relations to be expressed between elements without labeling the elements.

A friend of mine used this to his advantage when trying to remember important dates in computer history. Instead of sitting down and trying to remember everything, he printed over a hundred posters (each with a date and event) and plastered these throughout his house. His spatial memory is still so good that asked last week (more than a year since the experiment) when Lisp was invented, he replied that it was upstairs, around the corner from the toilet, so must have been around 1958.

Spreadsheets are also a wonderfully simple graphical representation of computational models.

Applications¶

Bundled with this module are several modules to help graph data structures (GraphViz::Data::Dumper), XML (GraphViz::XML), and Parse::RecDescent, Parse::Yapp, and yacc grammars (GraphViz::Parse::RecDescent, GraphViz::Parse::Yapp, and GraphViz::Parse::Yacc).

Note that Marcel Grunauer has released some modules on CPAN to graph various other structures. See GraphViz::DBI and GraphViz::ISA for example.

brian d foy has written an article about Devel::GraphVizProf for Dr. Dobb's Journal: http://www.ddj.com/columns/perl/2001/0104pl002/0104pl002.htm

Award winning!¶

I presented a paper and talk on "Graphing Perl" using GraphViz at the 3rd German Perl Workshop and received the "Best Knowledge Transfer" prize.

    Talk: http://www.astray.com/graphing_perl/graphing_perl.pdf
  Slides: http://www.astray.com/graphing_perl/

new¶

This is the constructor. It accepts several attributes.

  my $g = GraphViz->new();
  my $g = GraphViz->new(directed => 0);
  my $g = GraphViz->new(layout => 'neato', ratio => 'compress');
  my $g = GraphViz->new(rankdir  => 'BT');
  my $g = GraphViz->new(width => 8.5, height => 11);
  my $g = GraphViz->new(width => 30, height => 20,
                        pagewidth => 8.5, pageheight => 11);

The most two important attributes are 'layout' and 'directed'.

layout

The 'layout' attribute determines which layout algorithm GraphViz.pm will use. Possible values are:

directed

The 'directed' attribute, which defaults to 1 (true) specifies directed (edges have arrows) graphs. Setting this to zero produces undirected graphs (edges do not have arrows).

rankdir

Another attribute 'rankdir' controls the direction in which the nodes are linked together. The default is 'TB' (arrows from top to bottom). Other legal values are 'BT' (bottom->top), 'LR' (left->right) and 'RL' (right->left).

width, height

The 'width' and 'height' attributes control the size of the bounding box of the drawing in inches. This is more useful for PostScript output as for raster graphic (such as PNG) the pixel dimensions can not be set, although there are generally 96 pixels per inch.

pagewidth, pageheight

The 'pagewidth' and 'pageheight' attributes set the PostScript pagination size in inches. That is, if the image is larger than the page then the resulting PostScript image is a sequence of pages that can be tiled or assembled into a mosaic of the full image. (This only works for PostScript output).

concentrate

The 'concentrate' attribute controls enables an edge merging technique to reduce clutter in dense layouts of directed graphs. The default is not to merge edges.

orientation

This option controls the angle, in degrees, used to rotate polygon node shapes.

random_start

For undirected graphs, the 'random_start' attribute requests an initial random placement for the graph, which may give a better result. The default is not random.

epsilon

For undirected graphs, the 'epsilon' attribute decides how long the graph solver tries before finding a graph layout. Lower numbers allow the solver to fun longer and potentially give a better layout. Larger values can decrease the running time but with a reduction in layout quality. The default is 0.1.

overlap

The 'overlap' option allows you to set layout behavior for graph nodes that overlap. (From GraphViz documentation:)

Determines if and how node overlaps should be removed.

no_overlap

The 'no_overlap' overlap option, if set, tells the graph solver to not overlap the nodes. Deprecated, Use 'overlap' => 'false'.

ratio

The 'ratio' option sets the aspect ratio (drawing height/drawing width) for the drawing. Note that this is adjusted before the size attribute constraints are enforced. Default value is "fill".

bgcolor

The 'bgcolor' option sets the background colour. A colour value may be "h,s,v" (hue, saturation, brightness) floating point numbers between 0 and 1, or an X11 color name such as 'white', 'black', 'red', 'green', 'blue', 'yellow', 'magenta', 'cyan', or 'burlywood'.

name

The 'name' option sets name of the graph. This option is useful in few situations, like client side image map generation, see cmapx. By default 'test' is used.

node,edge,graph

The 'node', 'edge' and 'graph' attributes allow you to specify global node, edge and graph attributes (in addition to those controlled by the special attributes described above). The value should be a hash reference containing the corresponding key-value pairs. For example, to make all nodes box-shaped (unless explicitly given another shape):

  my $g = GraphViz->new(node => {shape => 'box'});
    

add_node¶

A graph consists of at least one node. All nodes have a name attached which uniquely represents that node.

The add_node method creates a new node and optionally assigns it attributes.

The simplest form is used when no attributes are required, in which the string represents the name of the node:

  $g->add_node('Paris');

Various attributes are possible: "label" provides a label for the node (the label defaults to the name if none is specified). The label can contain embedded newlines with '\n', as well as '\c', '\l', '\r' for center, left, and right justified lines:

  $g->add_node('Paris', label => 'City of\nlurve');

Attributes need not all be specified in the one line: successive declarations of the same node have a cumulative effect, in that any later attributes are just added to the existing ones. For example, the following two lines are equivalent to the one above:

  $g->add_node('Paris');
  $g->add_node('Paris', label => 'City of\nlurve');

Note that multiple attributes can be specified. Other attributes include:

height, width

sets the minimum height or width

shape

sets the node shape. This can be one of: 'record', 'plaintext', 'ellipse', 'circle', 'egg', 'triangle', 'box', 'diamond', 'trapezium', 'parallelogram', 'house', 'hexagon', 'octagon'

fontsize

sets the label size in points

fontname

sets the label font family name

color

sets the outline colour, and the default fill colour if the 'style' is 'filled' and 'fillcolor' is not specified

A colour value may be "h,s,v" (hue, saturation, brightness) floating point numbers between 0 and 1, or an X11 color name such as 'white', 'black', 'red', 'green', 'blue', 'yellow', 'magenta', 'cyan', or 'burlywood'

fillcolor

sets the fill colour when the style is 'filled'. If not specified, the 'fillcolor' when the 'style' is 'filled' defaults to be the same as the outline color

style

sets the style of the node. Can be one of: 'filled', 'solid', 'dashed', 'dotted', 'bold', 'invis'

URL

sets the url for the node in image map and PostScript files. The string '\N' value will be replaced by the node name. In PostScript files, URL information is embedded in such a way that Acrobat Distiller creates PDF files with active hyperlinks

If you wish to add an anonymous node, that is a node for which you do not wish to generate a name, you may use the following form, where the GraphViz module generates a name and returns it for you. You may then use this name later on to refer to this node:

  my $nodename = $g->add_node('label' => 'Roman city');

Nodes can be clustered together with the "cluster" attribute, which is drawn by having a labelled rectangle around all the nodes in a cluster. An empty string means not clustered.

  $g->add_node('London', cluster => 'Europe');
  $g->add_node('Amsterdam', cluster => 'Europe');

Clusters can also take a hashref so that you can set attributes:

  my $eurocluster = {
    name      =>'Europe',
    style     =>'filled',
    fillcolor =>'lightgray',
    fontname  =>'arial',
    fontsize  =>'12',
  };
  $g->add_node('London', cluster => $eurocluster, @default_attrs);

Nodes can be located in the same rank (that is, at the same level in the graph) with the "rank" attribute. Nodes with the same rank value are ranked together.

  $g->add_node('Paris', rank => 'top');
  $g->add_node('Boston', rank => 'top');

Also, nodes can consist of multiple parts (known as ports). This is implemented by passing an array reference as the label, and the parts are displayed as a label. GraphViz has a much more complete port system, this is just a simple interface to it. See the 'from_port' and 'to_port' attributes of add_edge:

  $g->add_node('London', label => ['Heathrow', 'Gatwick']);

add_edge¶

Edges are directed (or undirected) links between nodes. This method creates a new edge between two nodes and optionally assigns it attributes.

The simplest form is when now attributes are required, in which case the nodes from and to which the edge should be are specified. This works well visually in the program code:

  $g->add_edge('London' => 'Paris');

Attributes such as 'label' can also be used. This specifies a label for the edge. The label can contain embedded newlines with '\n', as well as '\c', '\l', '\r' for center, left, and right justified lines.

  $g->add_edge('London' => 'New York', label => 'Far');

Note that multiple attributes can be specified. Other attributes include:

minlen

sets an integer factor that applies to the edge length (ranks for normal edges, or minimum node separation for flat edges)

weight

sets the integer cost of the edge. Values greater than 1 tend to shorten the edge. Weight 0 flat edges are ignored for ordering nodes

fontsize

sets the label type size in points

fontname

sets the label font family name

fontcolor

sets the label text colour

color

sets the line colour for the edge

A colour value may be "h,s,v" (hue, saturation, brightness) floating point numbers between 0 and 1, or an X11 color name such as 'white', 'black', 'red', 'green', 'blue', 'yellow', 'magenta', 'cyan', or 'burlywood'

style

sets the style of the node. Can be one of: 'filled', 'solid', 'dashed', 'dotted', 'bold', 'invis'

dir

sets the arrow direction. Can be one of: 'forward', 'back', 'both', 'none'

tailclip, headclip

when set to false disables endpoint shape clipping

arrowhead, arrowtail

sets the type for the arrow head or tail. Can be one of: 'none', 'normal', 'inv', 'dot', 'odot', 'invdot', 'invodot.'

arrowsize

sets the arrow size: (norm_length=10,norm_width=5, inv_length=6,inv_width=7,dot_radius=2)

headlabel, taillabel

sets the text for port labels. Note that labelfontcolor, labelfontname, labelfontsize are also allowed

labeldistance, port_label_distance

sets the distance from the edge / port to the label. Also labelangle

decorate

if set, draws a line from the edge to the label

samehead, sametail

if set aim edges having the same value to the same port, using the average landing point

constraint

if set to false causes an edge to be ignored for rank assignment

Additionally, adding edges between ports of a node is done via the 'from_port' and 'to_port' parameters, which currently takes in the offset of the port (ie 0, 1, 2...).

  $g->add_edge('London' => 'Paris', from_port => 0);

as_canon, as_text, as_gif etc. methods¶

There are a number of methods which generate input for dot / neato / twopi / circo / fdp or output the graph in a variety of formats.

Note that if you pass a filename, the data is written to that filename. If you pass a filehandle, the data will be streamed to the filehandle. If you pass a scalar reference, then the data will be stored in that scalar. If you pass it a code reference, then it is called with the data (note that the coderef may be called multiple times if the image is large). Otherwise, the data is returned:

Win32 Note: you will probably want to binmode any filehandles you write the output to if you want your application to be portable to Win32.

  my $png_image = $g->as_png;
  # or
  $g->as_png("pretty.png"); # save image
  # or
  $g->as_png(\*STDOUT); # stream image to a filehandle
  # or
  #g->as_png(\$text); # save data in a scalar
  # or
  $g->as_png(sub { $png_image .= shift });

as_debug

The as_debug method returns the dot file which we pass to GraphViz. It does not lay out the graph. This is mostly useful for debugging.

  print $g->as_debug;
    

as_canon

The as_canon method returns the canonical dot / neato / twopi / circo / fdp file which corresponds to the graph. It does not layout the graph - every other as_* method does.

  print $g->as_canon;
  # prints out something like:
  digraph test {
      node [    label = "\N" ];
      London [label=London];
      Paris [label="City of\nlurve"];
      New_York [label="New York"];
      London -> Paris;
      London -> New_York [label=Far];
      Paris -> London;
  }
    

as_text

The as_text method returns text which is a layed-out dot / neato / twopi / circo / fdp format file.

  print $g->as_text;
  # prints out something like:
  digraph test {
      node [    label = "\N" ];
      graph [bb= "0,0,162,134"];
      London [label=London, pos="33,116", width="0.89", height="0.50"];
      Paris [label="City of\nlurve", pos="33,23", width="0.92", height="0.62"];
      New_York [label="New York", pos="123,23", width="1.08", height="0.50"];
      London -> Paris [pos="e,27,45 28,98 26,86 26,70 27,55"];
      London -> New_York [label=Far, pos="e,107,40 49,100 63,85 84,63 101,46", lp="99,72"];
      Paris -> London [pos="s,38,98 39,92 40,78 40,60 39,45"];
  }
    

as_ps

Returns a string which contains a layed-out PostScript-format file.

  print $g->as_ps;
    

as_hpgl

Returns a string which contains a layed-out HP pen plotter-format file.

  print $g->as_hpgl;
    

as_pcl

Returns a string which contains a layed-out Laserjet printer-format file.

  print $g->as_pcl;
    

as_mif

Returns a string which contains a layed-out FrameMaker graphics-format file.

  print $g->as_mif;
    

as_pic

Returns a string which contains a layed-out PIC-format file.

  print $g->as_pic;
    

as_gd

Returns a string which contains a layed-out GD-format file.

  print $g->as_gd;
    

as_gd2

Returns a string which contains a layed-out GD2-format file.

  print $g->as_gd2;
    

as_gif

Returns a string which contains a layed-out GIF-format file.

  print $g->as_gif;
    

as_jpeg

Returns a string which contains a layed-out JPEG-format file.

  print $g->as_jpeg;
    

as_png

Returns a string which contains a layed-out PNG-format file.

  print $g->as_png;
  $g->as_png("pretty.png"); # save image
    

as_wbmp

Returns a string which contains a layed-out Windows BMP-format file.

  print $g->as_wbmp;
    

as_cmap (deprecated)

Returns a string which contains a layed-out HTML client-side image map format file. Use as_cmapx instead.

  print $g->as_cmap;
    

as_cmapx

Returns a string which contains a layed-out HTML HTML/X client-side image map format file. Name and id attributes of map element are set to name of the graph.

  print $g->as_cmapx;
    

as_ismap (deprecated)

Returns a string which contains a layed-out old-style server-side image map format file. Use as_imap instead.

  print $g->as_ismap;
    

as_imap

Returns a string which contains a layed-out HTML new-style server-side image map format file.

  print $g->as_imap;
    

as_vdx

Returns a string which contains a VDX-format (Microsoft Visio) file.

  print $g->as_vdx;
    

as_vrml

Returns a string which contains a layed-out VRML-format file.

  print $g->as_vrml;
    

as_vtx

Returns a string which contains a layed-out VTX (Visual Thought) format file.

  print $g->as_vtx;
    

as_mp

Returns a string which contains a layed-out MetaPost-format file.

  print $g->as_mp;
    

as_fig

Returns a string which contains a layed-out FIG-format file.

  print $g->as_fig;
    

as_svg

Returns a string which contains a layed-out SVG-format file.

  print $g->as_svg;
    

as_svgz

Returns a string which contains a layed-out SVG-format file that is compressed.

  print $g->as_svgz;
    

as_plain

Returns a string which contains a layed-out simple-format file.

  print $g->as_plain;
    

Why do I get error messages like the following?¶

        Error: <stdin>:1: syntax error near line 1
        context: digraph >>>  Graph <<<  {

Graphviz reserves some words as keywords, meaning they can't be used as an ID, e.g. for the name of the graph. So, don't do this:

        strict graph graph{...}
        strict graph Graph{...}
        strict graph strict{...}
        etc...

Likewise for non-strict graphs, and digraphs. You can however add double-quotes around such reserved words:

        strict graph "graph"{...}

Even better, use a more meaningful name for your graph...

The keywords are: node, edge, graph, digraph, subgraph and strict. Compass points are not keywords.

See keywords <http://www.graphviz.org/content/dot-language> in the discussion of the syntax of DOT for details.

How do you handle XXE within XML?¶

Due to security risks with XXE in XML, Graphviz does not support XML that contains XXE. Thus it automatically prevents external entities being parsed by using the no_xxe option in XML::Twig when calling XML::Twig -> new(). And for this reason also the pre-reqs in Makefile.PL specify XML::Twig V 3.52.

See <https://metacpan.org/pod/release/MIROD/XML-Twig-3.52/Twig.pm#no_xxe>