Re: WWW/Internet 2009: 2nd CFP until 21 September
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 14 Aug 2009 10:49:43 -0300
Message-ID: <4a856b78$0$23747$9a566e8b_at_news.aliant.net>
>
> What is the difference between 'relational decomposition' and mere
> projection?
Date: Fri, 14 Aug 2009 10:49:43 -0300
Message-ID: <4a856b78$0$23747$9a566e8b_at_news.aliant.net>
paul c wrote:
>> ... >> >>> 1) in SQL, just what does decompositon of tables mean? Does it mean >>> what relational decomposition means, ie., lossless projection, or >>> something else? >> >> >> Relational decomposition doesn't mean lossless projection. The >> decomposed relations can contain extra tuples that don't show up in a >> join. Referential constraints are needed to prevent the extra tuples. >> ,,,
>
> What is the difference between 'relational decomposition' and mere
> projection?
Basically, he's making shit up as he goes along. There are any number of ways of decomposing relations. Lossless decomposition by projection/join is the basis for normalization, but that's by no means the only way to decompose relations. For example, another obvious way to decompose relations is by restrict/union. Received on Fri Aug 14 2009 - 15:49:43 CEST