presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/NodePrinter/visitSemiJoin
class NodePrinter:        @Override
        public Void visitSemiJoin(SemiJoinNode node, Void context)
        {
            printNode(node, "SemiJoin", format("%s = %s", node.getSourceJoinSymbol(), node.getFilteringSourceJoinSymbol()), NODE_COLORS.get(NodeType.JOIN));

            node.getSource().accept(this, context);
            node.getFilteringSource().accept(this, context);

            return null;
        }