Re: Modeling General Graphs in SQL

From: paul c <toledobythesea_at_oohay.ac>
Date: Wed, 28 Dec 2005 16:55:35 GMT
Message-ID: <bszsf.211442$Gd6.189170_at_pd7tw3no>


dawn wrote:
> Marshall Spight wrote:
>

>>mikharakiri_nospaum_at_yahoo.com wrote:
>>
>>>The minimum path query is the same as transitive closure, which is
>>>widely believed to be inexpresible by standard SQL.
>>
>>I was under the impression that it was proven, rather than "widely
>>believed." Am I mistaken? Is this one of those things that's not
>>been proven one way or the other?

>
>
> You are correct. It has been proven that transitive closure is not
> possible in SQL. There are ACM papers and others. If you google for
>
> sql transitive-closure
>
> there are many relevant resources, some with a proof and others which
> introduce possible extensions to SQL for transitive closure.
> --dawn
>

 From "Universality of Data Retrieval Languages" by Alfred V. Aho and Jeffrey D. Ullman:

"In this appendix. we prove that the transitive closure of a relation cannot be couched as an expression of relational algebra."

p Received on Wed Dec 28 2005 - 17:55:35 CET

Original text of this message