MPTCs and functional dependencies

Henrik Nilsson nhn at Cs.Nott.AC.UK
Mon Apr 10 11:10:34 EDT 2006

Hi all,

Manuel Chakravarty wrote:
 > > My conclusion is that we should not include FDs or ATs into the
 > > standard at the moment.  Standardising FDs as a stopgap measure may
 > > easily put us into the same situation that we are having with
 > > records at the moment.
 > > Nobody is really happy with it, but we don't dare to change it
 > > either.

Martin Sulzmann

 > The situation here is clearly different. Whatever comes next
 > (after FDs) will be a conservative extension. So, standardising
 > FDs is a good thing because they have proven to be a useful (somewhat
 > essential for MPTCs) feature. Hence, I will go with Simon:
 > H' should have MPTC + FDs, but not ATs.

I basically agree with Simon PJ and Martin:

MPTCs are necessary for H', and MPTCs pretty much necessitates
at least some limited form of FD/AT.

Thus I view FD/AT as so important, that I think it is a secondary
concern if it ends up being a stop gap measure.

Moreover, it seems to me that FD/AT declarations in practical
applications amounts to very little code. Thus, the likely work
impact if FD/AT is completely replaced with some other mechanism
providing the same functionality should be very limited.

This is unlike records, say, where record notation is likely to be
used pretty much throughout an application.

Also, the alternative of NOT having FD/AT would seem to lead
to rather convoluted solutions in many cases, so the work of
adapting non FD/AT MPTC code to an hypotetical H'' setting
where an FD/AT replacement is available, is potentially quite

But of couse, the above discussion on likely change
impact is just my gut feeling.

My key argument is that MPTCs and thus some form  of FDs/ATs
are really important in practice.

All the best,


Henrik Nilsson
School of Computer Science and Information Technology
The University of Nottingham
nhn at

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