version compare and partial orgls

[Mark S. Miller <mark>]

Date: Fri, 1 Sep 89 20:42:48 PDT
   From: michael (Michael McClary)

   i.e., one tells it more about what points to it, and the other tells
   it more about what it points to.  (An interesting distinction in a
   doubly-linked structure.  If you turn the Ent upside-down, does
   inform become unify and vice-versa?)

I believe both simply tell it more about what it points to.  Inform
(now called data-inform) tells it about something that it didn't
previously know it pointed to at all, and Unify (now called
sharing-inform) tells it better identity information about what it
already knew it pointed to.  I.e., it knew it pointed to an 'a' there,
but it didn't know that much about who that 'a' was.  After a
sharing-inform, it knows more about who that 'a' is.

We have derived many useful insights from the bilateral (equatorial)
symmetry of the ENT.  

OH, I SEE WHAT YOU MEAN (sudden flash).  A DataObject whose canonical
EAddress is in terms of a given DataStamp does in fact point at that
DataStamp (as well as having that DataStamp point at it).  Data-inform
gives a DataStamp new DataObjects to point to and to have point back
at it (with EAddress).  Sharing-inform changes the DataObjects you
point to so they no longer point back at you (with EAddress, they of
course point back at you anyway, but that's implementation, not
semantics).  In any case, I don't think this is a case where turning
the ENT upside yields anything.

   Does it make sense to EVER freeze a DataStamp?  If someone can make
   a virtual copy, why can't they make a real copy, then unify it?
   What am I missing?

A virtual copy would be a MapStamp, and would not itself be informable
(since the ability to look at something implies the ability to copy
it, but not the ability to inform the original).  If you make a real
copy, then you have the same data in the sense of bits, but whole new
DataObject identities.  You can unify (sharing-inform in the new
terminology as of today) this freely with whatever you want, but this
won't effect the original.  If you sharing-inform it to the original,
it still won't affect the original, and you will not be able to
further sharing inform it, so you still won't be able to affect the
original.