Re: Object Class and Data Type
Date: Mon, 5 Apr 2004 08:45:02 -0400
DEC RDB supported domains (called global fields) way back in 1983. But it did not prohibit joins across domains. In 1986, when they added support for SQL, they put in a create domain command.
However, it was easy to find joins across domains by a query on the metadata.
I haven't tracked RDB since 2001, so they may have added it.
The reason I ask is that DEC's data dictionary at first made the record the most basic dictionary item. There was a huge debate, and eventually the domain was added as the fundamental lexical entry.
IIRC, Martin wrote on this subject, back in the 1970s.
Now I have two other questions:
First, when did CREATE DOMAIN make it into mainstream SQL? Second, does the relational model have an equivalent concept? I would think it would have to, given the definition of a relation. Received on Mon Apr 05 2004 - 14:45:02 CEST