[sc34wg3] Look Ma! No Properties!

[Robert Barta]

On Fri, Jul 23, 2004 at 10:56:38PM +0200, Jan Algermissen wrote:
> Robert,
> 
> I had posted two other questions about your proposal. Maybe you missed
> them. Here they are again:

Jan,

My apologies, I thought I had covered this in the other mails.

> Robert Barta wrote:
> > 
> > On Thu, Jul 15, 2004 at 08:08:11PM -0400, Patrick Durusau wrote:
> > 
> > > Ok, the \tau model has no properties.
> > 
> > The \tau model is based on assertions only. Properties are seen as
> > only a special form of an assertion, yes.
> 
> Uhm...I don't get it. How are properties seen as a special form of
> assertion?

If you look at the property 'shoesize' which is attached to a person,
then you would have assertions of the form:

  {  < person: rho >, < shoesize: 42 > }

What I find always appealing in this 'relativistic' view of the world
is that objects are going away completely and are reduced to
dots. Everything else is interaction with something else.

> > Just to make an example to avoid a too abstract discussion: Lets
> > assume we model students with their names, their shoesize and their
> > student ID (SID). In the 'assembler-like' tau model we would only have
> > assertions:
> > 
> >  { < name-haver:     jack-learner >, < name     : "Jack Learner" > },
> >  { < shoesize-haver: jack-learner >, < shoesize : 1234 > }
> >  { < sid-haver:      jack-learner >, < SID      : 12345678 > }
> 
> I guess I am missing the step how you group together the assertions that
> have members (r1,p1),(r2,p1),(r3,p1) with p1 E N     (not I !!)
> and how this enables the forall semantics on p1, allowing you to
> view name,shoesize and SID as properties.

Hmmm, with 'grouping' you mean 'identification'? In that case, since
p1 is the same everywhere it is the same thing in all members. Names
are similar to IDs, except that behind a name could be a huge
things. You cannot see it, though.

The 'forall semantics' is not directly applicable here as the model
itself does not have any semantics. It is like a skeleton. Structure,
but no movement, no action.

The 'forall semantics' (and reciprocal the 'exists') kicks in if you
introduce quantifiers into queries and constraints. You need them
to express queries like

 "give me all computer clusters in my network where all machines
  are down"

\rho