Re: By The Dawn's Normal Light

From: Dawn M. Wolthuis <dwolt_at_tincat-group.comREMOVE>
Date: Fri, 22 Oct 2004 16:31:06 -0500
Message-ID: <clbu73$csv$1_at_news.netins.net>


"Laconic2" <laconic2_at_comcast.net> wrote in message news: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'
>
> In this case, I take the same view you do, that distinguishing between
the
> relational engine and the type engine is useful, at least at the
conceptual
> level.
>
> 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 a student is enrolled in these courses: {'CS101', 'PSYCH101', 'ENG101',
> 'MATH101'} the student has the same SET of courses as the criterion. But
> does not have the same LIST of courses as the criterion. Thus the
> distinction between a SET and a LIST is critical to the type engine. IMO,
> of course.
>
>
> If I got it right, it is this third case that distinguishes the RDM from
> the Nelson-Pick model.
>
>
On first read, this sounds right to me.

This is only one of the differences, but one of the ones that I note as helping to make Pick a more productive database environment for software development than an RDBMS. It looks like I have a bit of reading to catch up on. I'll try to keep from replying to each. --dawn Received on Fri Oct 22 2004 - 23:31:06 CEST

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