Re: OO and relation "impedance mismatch"

From: Laconic2 <laconic2_at_comcast.net>
Date: Mon, 4 Oct 2004 07:27:14 -0400
Message-ID: <NbKdnQLB1r46rvzcRVn-qg_at_comcast.com>


"Troels Arvin" <troels_at_arvin.dk> wrote in message news:pan.2004.10.04.07.09.31.918874_at_arvin.dk...

> A bit if confusion seems to have crept into this thread:
>
> In PostgreSQL, CREATE DOMAIN may be used to create a "nichname"/macro for
> a column definition. As such, it isn't used to create new types.

In DEC Rdb, my point of reference, CREATE DOMAIN is more than a "macro for defining columns", and less than a feature for creating types. The reason it's more than a macro is that the relationship between a domain and all columns that depend on it is maintained in the metadata. This allows a kind of domain based data analysis to be done on an Rdb database with trivial SQL queries, never mind some pricey tool.

The absence of any metadata in an Oracle database that indicates that two columns are drawn from the same domain causes the same kind of analysis of Oracle databases to be based on column names and formats, inference, guesswork, and documentation. Or some pricey tool that does the same thing automatically.

Domains are really the "data elements" of table design.

Getting back to your point, I tried to keep the distinction between user defined domains and user defined types in my original post, but you are right: some confusion has crept in. Received on Mon Oct 04 2004 - 13:27:14 CEST

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