Re: Hierarchies in the relational model

"Mikito Harakiri" <mikharakiri_at_iahu.com> wrote in message news:<l5Ykb.22$Rt2.193_at_news.oracle.com>...
> The big(?) problem seem to be that for a transitevely derived edge, e.g.
> 1->4, there is more than one path, so that one have problem identifying all
> the paths in the first place.
>
> It's impossible to write a query returning all the paths in datalog or SQL
> (with recursive syntax), because the output will be of size exponential in
> the size of the input, and it's well-known that datalog and SQL (meaning:
> RA+recursion+aggregation+arithmetic) cannot do it.
>
> The answer was kindly provided in private email exchange by Leonid Libkin.

I've just found this article by Leonid:
http://citeseer.nj.nec.com/407307.html
which is a very accessible discussion of the limitations of the relational model, and how things like grouping, arithmetic operations, aggregation and recursion can be "bolted on" to give a more useful query language.

I wonder if these additions can be somehow incorporated into an extended relational model instead of being added on as a kind of afterthought? And whether such a thing is in fact necessary or desirable?

Paul. Received on Tue Oct 21 2003 - 15:28:51 CEST