presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/GraphvizPrinter/printEdge
class GraphvizPrinter:        private void printEdge(PlanNode from, PlanNode to)
        {
            String fromId = idGenerator.getNodeId(from);
            String toId = idGenerator.getNodeId(to);

            output.append(fromId)
                    .append(" -> ")
                    .append(toId)
                    .append(';')
                    .append('\n');
        }