Re: What to call this operator?

In article <1120230564.593323.241990_at_g43g2000cwa.googlegroups.com>, marshall.spight_at_gmail.com says...
> > > With join, all keys are preserved.
> >
> > Umm... they are? What do you mean by "preserved"? Perhaps I
> > misunderstand you, but a key of one of the operands is not necessarily a
> > key of the result.
>
> Okay. What rule would you propose?

I'm not sure I understand you. Surely the keys of a join result are determined by logic, not by rules one might propose? Date and Darwen(?) has explored this, in connection with their work on view updating. Off the top of my head, it depends on whether keys of the operands are subsets of the join attributes.

-- 
Jon