On Jan 30, 2009, at 1:46 PM, Schiffel, Jeffrey A wrote: (01)
>> 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. Or am I
> missing
> something?
> (02)
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)
PatHayes (04)
> -- Jeff Schiffel
>
> _________________________________________________________________
> Message Archives: http://ontolog.cim3.net/forum/ontolog-forum/
> Config Subscr: http://ontolog.cim3.net/mailman/listinfo/ontolog-forum/
> Unsubscribe: mailto:ontolog-forum-leave@xxxxxxxxxxxxxxxx
> Shared Files: http://ontolog.cim3.net/file/
> Community Wiki: http://ontolog.cim3.net/wiki/
> To join: http://ontolog.cim3.net/cgi-bin/wiki.pl?WikiHomePage#nid1J
> To Post: mailto:ontolog-forum@xxxxxxxxxxxxxxxx
>
>
> (05)
------------------------------------------------------------
IHMC (850)434 8903 or (650)494 3973
40 South Alcaniz St. (850)202 4416 office
Pensacola (850)202 4440 fax
FL 32502 (850)291 0667 mobile
phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes (06)
_________________________________________________________________
Message Archives: http://ontolog.cim3.net/forum/ontolog-forum/
Config Subscr: http://ontolog.cim3.net/mailman/listinfo/ontolog-forum/
Unsubscribe: mailto:ontolog-forum-leave@xxxxxxxxxxxxxxxx
Shared Files: http://ontolog.cim3.net/file/
Community Wiki: http://ontolog.cim3.net/wiki/
To join: http://ontolog.cim3.net/cgi-bin/wiki.pl?WikiHomePage#nid1J
To Post: mailto:ontolog-forum@xxxxxxxxxxxxxxxx (07)
|