entity, creation and destruction

We were discussing "entity" again today...

At least one person defined "entity" as "a description of a thing"
based on the definition they read here --

   http://www.w3.org/2011/prov/wiki/FormalSemanticsStrawman#Entities

   An entity is a kind of object that describes a time-slice 
   of a thing, during which some of the thing's attributes 
   are fixed. 

I submit that an "entity" is a "thing" which is identified by
some set of immutable characteristics (which set may or may not
be fully defined -- much as philosophy continues to debate what
set of immutable characteristics defines a particular person,
the more so given such personality changes as may be observed
following various injuries or pharmaceutical treatments).

When an immutable characteristic changes, one entity becomes 
another.  When a mutable characteristic changes, the entity
remains the same, but its description (and one might say, its 
provenance) changes.


That discussion arose in context of the "Entity Invalidation"
proposal found here --

   <http://dvcs.w3.org/hg/prov/raw-file/default/model/working-copy/wd5-prov-dm-misc.html#Proposal%201:%20On%20Entity%20Invalidation>

The examples seen there were confusing (conflating a web address
with the entity/ies to which the address may be dereferenced) and
not compelling to the audience at hand.

I had some hopefully more compelling, and also hopefully less 
confusing, examples which I was asked to post to the list.

Herewith...


A "tree" comprises some amount of "wood".  When the "tree" is 
felled, one might say it is no longer a "tree" (it no longer
stands; the stump which remains was once an integral part of 
the tree; it no longer sprouts leaves; etc.)...

Let us say that the wood which comprised the bulk of that tree 
is transformed into a table.

The table is a new entity -- immutable characteristics include
the carpenter who constructed it, the "tabletop" surface on
which things may be placed, and the legs which hold it off the
floor.  

Mutable characteristics not relevant to its "table-ness" include 
its color, its exact shape, its height. I might cut a round table 
into a square, paint it, or shorten its legs, without it becoming 
a new entity. 

If any of the immutable characteristics are removed or destroyed 
-- for instance, if the whole is broken into pieces such that it 
cannot perform as a table -- the "table" entity is no more.

However -- the wood remains.

In the framework of the "entity" definition I quoted earlier, the 
"table" is a time-slice of the "wood".  The *tree* is a time-slice 
of the "wood".  Many characteristics of the wood change -- but it 
remains the wood of the original tree.

At some point, the wood -- even the entire table -- may be thrown
on a bonfire, and the entirety may be consumed.

The table entity is no more -- the required characteristics are 
no longer present.

The *wood* entity is no more -- it has been consumed by fire, and
transformed into ash.


During the call, I suggested another example which (I think) lends
strong support to the need for a "destruction" or similar construct
which corresponds to "generation" or "creation".

A "Great Master" "creates" a "painting".  The "painting" "hangs"
in a "museum".  The "museum" and all works therein are "consumed"
by a "fire".  Witnesses see this particular "painting" so "consumed".
Years later, a "painting" looking very much like the original comes 
up for auction... 

Real-world Provenance cries out for the ability to say that the
museum piece *was* destroyed, so this work being auctioned 
*cannot* be (or at least, it is highly doubtful that it is) the 
same entity.  Real-world Provenance also allows for the possibility
that the entity consumed in the fire was not the "original" which
is now on auction -- that the burned painting was a forgery...

But *something* was burned, was destroyed, can no longer be sold.


Hopefully this exploration is helpful ...

Regards,

Ted




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