Traffic Lights

##"I played some days with making an interface between our ConceptBase system (essentially a database system to store models) and graphviz. One example graph is attached. It is a so-called petri net for Dutch traffic lights. The example is actually taken from a book by Wil van der Aalst." Contributed by Manfred Jeusfeld.

##Command to produce the output: "neato -Tpng thisfile > thisfile.png"

digraph TrafficLights {
fontname="Helvetica,Arial,sans-serif"
node [fontname="Helvetica,Arial,sans-serif"]
edge [fontname="Helvetica,Arial,sans-serif"]
layout = neato
node [shape=box];  gy2; yr2; rg2; gy1; yr1; rg1;
node [shape=circle,fixedsize=true,width=0.9];  green2; yellow2; red2; safe2; safe1; green1; yellow1; red1;
gy2->yellow2;
rg2->green2;
yr2->safe1;
yr2->red2;
safe2->rg2;
green2->gy2;
yellow2->yr2;
red2->rg2;
gy1->yellow1;
rg1->green1;
yr1->safe2;
yr1->red1;
safe1->rg1;
green1->gy1;
yellow1->yr1;
red1->rg1;

overlap=false
label="PetriNet Model TrafficLights\nExtracted from ConceptBase and layed out by Graphviz"
fontsize=12;
}