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Re: [ontolog-forum] Is there something I missed?

To: "[ontolog-forum] " <ontolog-forum@xxxxxxxxxxxxxxxx>
From: "Schiffel, Jeffrey A" <jeffrey.a.schiffel@xxxxxxxxxx>
Date: Mon, 2 Feb 2009 17:42:40 -0600
Message-id: <ECF42862FCA16D41BFA98F8C45F0955405723CB7@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>

>> 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.
Reply from Jeff Schiffel
> 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. Or am I    (01)

> missing something?
>    (02)

Pat Hayes adds:
Thats one way to think about it. But another way is that each column of
the table is a binary (!) relation holding between the table and the
rows, which are entities. This is the same switcheroo which takes an
n-ary relation into a collection of binary 'case roles' (think column
names) in the format beloved of linguists. Basically, its the rather
trite observation that a 2-d table can be thought of either as a vector
of rows or a vector of columns. Both ways work.    (03)

Jeff again:    (04)

Yes, but I tend not to think about it that way, probably due to my
information systems background. Your point, however, is very good, if I
catch your meaning. Let's say I find a relation that isn't binary by
itself between a column and the table. Then I have found a candidate for
normalization, since it is a masquerading binary that should be further
decomposed (into another table where the dependent attribute becomes
binary with the new table).    (05)

-- Jeff Schiffel    (06)

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