# Re: constraints in algebra instead of calculus

From: paul c <toledobythesea_at_oohay.ac>

Date: Sun, 17 Jun 2007 15:26:11 GMT

Message-ID: <nocdi.34285$1i1.7008_at_pd7urf3no>

>>where the result has one row.

>>It looks to me that the TTM def'n,

Date: Sun, 17 Jun 2007 15:26:11 GMT

Message-ID: <nocdi.34285$1i1.7008_at_pd7urf3no>

Jon Heggland wrote:

> paul c wrote: >

*>>I think you are suggesting:**>>**>>R{B} GROUP {B} as gB:**>>gB**>>{2,3}**>>*>>where the result has one row.

> > > Yes. In general, any R{X} GROUP {X} as gX will produce a relation with > one tuple, containing a sole attribute gX with R{X} as its value. > (Unless R{X} is empty, of course.) > >

>>It looks to me that the TTM def'n,

*>>**>>"Let relation r have attributes A, B, ..., C, D, E, ..., F. Then the**>>Tutorial D <group>**>>r GROUP ( { D, E, ..., F } AS X )**>>is shorthand for the Tutorial D expression**>>( EXTEND r ADD ( r AS RR , RELATION { TUPLE { A A, B B, ..., C C } } AS*

*>>TX , RR COMPOSE TX AS X ) ) { A, B, ..., C, X }**>>(where RR and TX are attribute names not already appearing in r),**>>and can therefore be expressed in A."**>>**>>I read that as meaning that the COMPOSE joins the original relation with**>>each original tuple,*> > > No, it joins the original relation with (a singleton relation > containing) a tuple consisting of the non-grouped attributes of each > original tuple---note that the TUPLE expression only includes A, B, ..., > C; not D, E, ..., F. In this case, the set of non-grouped attributes is > empty; hence, the RELATION { ... } expression is TABLE_DEE. > ...

Jon, thanks very much, that seems now to point out a basic blunder of mine in the previous posts. Apologies to all for the resulting mistakes. I'll have to go and re-visit whatever mysticism I had in mind, maybe I was thinking of an operator that should be called DUPE or GROPE, not TTM GROUP.

p Received on Sun Jun 17 2007 - 17:26:11 CEST