Re: Composite type

Huge question.  You might find my blog (http://ledgersmbdev.blogspot.com) to be of interest.

Here's the very brief overview.

1.  Every good object-relational design is also good relational design to at least a certain extent.  With a few exceptions (which, if they don't strike you as necessary, they probably aren't exceptions), you don't want to sacrifice relational design in the process.  Usually if you are going to sacrifice relational design (up to and including 1st Normal Form) you should have a very good reason to do so.  Sacrificing relational design always has costs.  Don't do it willy nilly.

2.  Table inheritance in PostgreSQL works better when you think less in terms of inheritance and more in terms of mix-ins.  This is because certain things, like keys, don't inherit the way you'd expect in an inheritance approach.  Table inheritance in PostgreSQL is a wonderful tool for maintaining consistent interfaces across necessarily different tables (for example because foreign keys are different).  However it doesn't work flawlessly for things like managing subtypes.  Use joins (and maybe views) for that.

3.  You can treat tables as classes, and build methods on those.  You can also treat views as classes and build methods on those.  This allows you to encapsulate your data in other ways.  Complex types can be classes too.

I usually think about object-relational design not in terms of the table layout but in terms of certain styles of writing functions and ways of interacting with the underlying data.  In other words, for me it is about ways of encapsulating logic both above and below SQL so that various kinds of complex operations are gracefully handled with looser coupling between the application and the database.

Going very far on this will require writing client libraries.  I am working on some in Perl.  I would be happy to collaborate with those in other languages.  However it's best to start small, and experiment with adding a little bit at a time to a good relational design, and see what it buys you.  In this area, I think, less is quite often more.