On Fri, Jan 30, 2009 at 2:46 PM, Schiffel, Jeffrey A
<jeffrey.a.schiffel@xxxxxxxxxx> wrote:
>> From: Patrick Cassidy
>
>> In the RDB's I have seen, each field (column in a table) often
> (typically?)
>> represents one relation on the type represented by the table, so the
> number
>> of columns does not have any relation to the arity of the relations
> used.
>> Two or more columns can be used together to represent higher-arity
>> relations, but they may be quite independent.
>
> I'm not certain I know what you mean. In an entity-relationship isn't
> the relation the entire row, not just one column? The entity is the name
> of the table. The names of the columns are the identifiers of an n-ary
> relation. Each row is an instance of the n-ary relation. (01)
Yes to all of those. (02)
> Or am I missing something? (03)
I think PC's point is that it is -possible- to extract lower arity
relations from a large arity one. (04)
My point, which is not contradictory to that, is that -most- db
tables/relations I see are spelled out as ternary or greater, whatever
the relations that it -could- be reduced to. (05)
But reverse direction point of mine is that whatever the cogency of a
database is to a human reader, one can still artificially reduce the
max arity, and still preserve...let me see...correctness. (06)
(I'm just trying to be explicit about technical meanings of words
-and- real world experience). (07)
Mitch (08)
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