updating on views

Hi!

I'd like to bother you with something about updating views. At present, postgresql7.3　doesn't support update on views.When I look up the source code, I see that view is implemented with rules. That is when a view is created, a corresponding ‘select'　rule is created too. And I see the following code:

#ifdef NOTYET
RuleStmt *replace_rule;
RuleStmt *append_rule;
RuleStmt *delete_rule;
#endif
.. ...

#ifdef NOTYET
replace_rule = FormViewReplaceRule(view, viewParse);
append_rule = FormViewAppendRule(view, viewParse);
delete_rule = FormViewDeleteRule(view, viewParse);
#endif
.. ...

In my eyes, it is not very difficult to realize view update with fill the above three functions。But I know the developers of postgresql are very learned, now that they didn't realize view update, maybe it is very difficult. I am a beginner of postgresql, so with my limited knowlege, maybe I can't realize the difficulity of doing such a thing.
So I wonder if some of you would like to give me some advice about updating on views or why it is not realized、what's the difficulty of doing it?

Long for your reply.
Thank you!

Best regards!

　　　　　　　　Yours XiaojingLi
　　　　　　　　qqjasmine(at)hotmail(dot)com
　　　　　　　　　　2002-11-23