Re: Mixing OO and DB

On Feb 11, 8:30 am, S Perryman <q..._at_q.com> wrote:
> Tegiri Nenashi wrote:
> > On Feb 8, 11:32 am, "Dmitry A. Kazakov" <mail..._at_dmitry-kazakov.de>
> > wrote:
>
> SP>For me, the big problem has always been the following :
>
> SP>SomeType = (x,y,z) (or if you prefer : type SomeType { x, y, z } etc)
>
> SP>s = SELECT SomeType FROM Somewhere WHERE (x = 123) ;
>
> SP>In the OO world, the problem is that for each instance of SomeType held
> SP>in Somewhere, the *implementation* of the property 'x' could be merely
> SP>an actual data value, or a serious computation process. That is the ADT/OO
> SP>way.

(removed confusing exchange)
Unless you state your problem in more detail -- I suggest one page description -- I fail to understand it.

> FP is perfectly capable of accommodating RA.
> Because RA is based on mathematical concepts, as is FP.
>
> Therefore any computable predicate expressible in RA, can be expressed in
> FP.

This argument is too weak. There are plently of incompatible mathematical models.

> There is nothing inherent in the relational model, or regexps, that prevent
> the latter being defined in terms of the former (ie confirming my comment
> above about implementations) .

No, one fundamental difference between the two models is the properties of the join operation. In regular expressions join is not commutative. For example the result of concatenating "ab" with "cde" depends on the order. In relational algebra join is commutative. The other huge difference is that in RA join is compatible with set intersection; basically intersection is a join. In regular expressions algebra intersection can't be expressed via join. Received on Mon Feb 11 2008 - 20:02:06 CET