Re: Concurrency in an RDB

Sampo Syreeni wrote:
> Given the current, practical importance of both running text and the RM,
> I wonder why a) there haven't been any genuine attempts at treating
> strings, text and language in general in relational terms, or b) why the
> RM folks won't confess it can't be done, given the current state of
> knowledge, thereby acknowledging that there is data that just isn't
> currently amenable to relational treatment.

What "text" do you have in mind? A set of strings is formalized nicely as Kleene algebra. relational algebra is also Kleene algebra.

Seriously, the parallels between Kleene algebra and relational algebra (in Codd's definition, not Tarski:-) are remarkable. If one accepts that join and union are the 2 fundamental operators of relational algebra, and agrees that Kleene star is somewhat less important operator, than both algebras hinge on join and union. The fundamental difference is that relational join is commutative, while Kleene's is not. Received on Fri Dec 29 2006 - 04:19:37 CET