[sc34wg3] Look Ma! No Properties!

[Jan Algermissen]

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?

> 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.

> forall [ $s1
>          SID: $sid1 ]
>    => not exists [ $s2
>                    SID: $sid1 ]

If I got that right....

This might reveal that I did not study (and not fully understand section 2
of tau, but I would be very thankfull for an explanation in prose.

Question on 2.1:
I assume that the assertions in the tuples (a1,a2,...an) all have the
same set of roles, yes? If not, how would the projection operator work?

I am missing how you determine that two assertions have the same set
of roles?


I guess I just miss that, can you explain?

Jan

> 
> The machinery would conclude - trivially - that it is the SID property
> alone that signals an identity.
> 
> If - for some weird reason - the shoesize and the first letter in the
> name are involved, then we would write (brrrrr):
> 
> forall [ $s1
>          name     : $name1
>          shoesize : $shoesize1
>          SID      : $sid1 ]
>    => not exists [ $s2
>                    name     : $name2 =~ /^$name1[0:1]/
>                    shoesize : $shoesize1
>                    SID      : $sid1 ]
> 
> So the SID AND the shoesize and the first letters have to be different
> and - together - induce identity.
> 
> Many more bizarre concepts of 'identity' are possible.
> 
> > What is puzzling to a degree, assuming you have the time to address the
> > first issue, is where are topics/subjects, etc.
> 
> The \tau model does not mention topics (= subject proxies in your
> diction) because these collapse into identifiers. These identifiers
> are involved in assertions.
> 
> Does this make things clearer?
> 
> \rho
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-- 
Jan Algermissen                           http://www.topicmapping.com
Consultant & Programmer	                  http://www.gooseworks.org