Re: By The Dawn's Normal Light
Date: Fri, 22 Oct 2004 13:44:30 -0400
Message-ID: <v7KdnTYJA9OV2uTcRVn-hg_at_comcast.com>
Paul,
There are three ways a value might be "non atomic"
The first is that the values might contain some substructure within their
representation.
In addition to LAST_NAME LIKE 'L%' we could have SUBSTRING(LAST_NAME, 1, 3)
= 'ACO'
The second is that the values might themselves be tuples. That is, a column like NAME might be made up of three named components, namely NAME.FIRST, NAME.MIDDLE, and NAME.LAST. Date is quite clear in stating that this is NOT encapsulation. As far as I'm concerned NAME.FIRST is no more and no less concealed than NAME_FIRST.
The third is that the values might be sets.
SELECT s.id, s.name
FROM enrollments s
WHERE s.courses_enrolled = {'PSYCH101', 'ENG101', 'MATH101', 'CS101'}
Now the question of whether courses_enrolled is a "set" meaning unordered, or a "list" meaning ordered is crucial for the correct interpretation of the equality test.
If I got it right, it is this third case that distinguishes the RDM from the Nelson-Pick model. Received on Fri Oct 22 2004 - 19:44:30 CEST