// new ScalarVisitor( plan, pigContext ).visit();
CompilationMessageCollector collector = new CompilationMessageCollector() ;
new TypeCheckingRelVisitor( plan, collector).visit();
new UnionOnSchemaSetter( plan ).visit();
new CastLineageSetter(plan, collector).visit();
// new ColumnAliasConversionVisitor( plan ).visit();
// // validate
// CompilationMessageCollector collector = new CompilationMessageCollector() ;
// TypeCheckingRelVisitor typeChecker = new TypeCheckingRelVisitor(plan, collector);