Distinguish view and table problem

I just want to distinguish a view and a table while postgres execute exec_simple_query(). In the systable of pg_class, a view and a table has different relkind ('r' 'v'). But when I print the parsetree and the rewrite parsetree, I found that a view and a table has no character to distinguish because the structure Relation has no attribute called relkind. Maybe I should read systable to confirm that we are select from a view or table? But there's still has problem. How could I get the relkind of a table(view) by its name from pg_class?

Another question is that does postgres save the user's original query_string at anywhere(systable etc.)? If I want to save the sourceText in the systable, I could add a column to pg_class called query_string. How could I insert a line to pg_class or read a line from it?

 

Thank you very much!