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Re: repeating groups

From: Jonathan Leffler <jleffler_at_earthlink.net>
Date: Sun, 19 Feb 2006 03:19:48 GMT
Message-ID: <otRJf.1772$VI6.209@newsread1.news.pas.earthlink.net>


mAsterdam wrote:

> Marshall Spight wrote:

>>>[...snippage...]
>> Sure. But there are several ways out of the repeating groups problem
>>
>> 1) decomposing relations, aka "classical" 1NF
>> 2) higher-than-1 cardinality attributes: lists or sets
> 
> Aren't you jumping over the "order may have meaning" problem
> here by taking these two together?

It depends whether you take the OR in 'lists or sets' to be inclusive or exclusive, doesn't it? If it is inclusive, then lists handle the 'order has meaning' case and sets handle the 'order is not significant case'. But you've complicated the algebra - instead of just sets, you've now got to deal with lists and sets (and the alternatives you list below).

>> 3) Fully nested relations.

> 
> lists-of-lists? sets-of-sets? lists-of-sets? sets-of-lists?
> 

>> Actually, 2) was something I hadn't really thought of before:
>> add *one* level of nesting. This idea is interesting but less
>> appealing than 3, because it is less regular. I tend to prefer
>> orthogonal designs; they have fewer arbitrary limitations.

Was it Hoare who said "anything in computer science that isn't recursive isn't any good" or words to that effect? (I found two references at Google to Jim Gray saying "Anything in computer science that's not recursive is no good", but it is not an easy expression to search for.)

1-level of nesting would be arbitrary and would very quickly become restrictive. Indeed, you'd have to be very careful not to lose the closure property of the algebra.

 >[...snippage...]

-- 
Jonathan Leffler                   #include <disclaimer.h>
Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com
Guardian of DBD::Informix v2005.02 -- http://dbi.perl.org/
Received on Sat Feb 18 2006 - 21:19:48 CST

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