[sc34wg3] Comments on Tau model

[Lars Marius Garshol]

--- HIGH-LEVEL COMMENTS

I guess my key question for the author of this model is why he chose
the particular structure he did. As far as I can tell, almost any
underlying structure would have served the purpose, since it is the
operations that do the job. To put it another way, couldn't the exact
same set of operations have been used on a quad model? Or on some
third model?

The structure of Tau assertions is, it seems, different from both the
structure of TMRM assertions and TMDM associations. As far as I can
tell, there is no groupings of players of the same role (role type in
TMDM), nor does there appear to be any support for assertion types. Or
is that supposed to be indicated with some undefined role type?

--- DETAIL

  "Literals may be numbers of quoted strings"

Why just two types? In fact, why are the types specified at all? As
far as I can see they aren't used anywhere.

What is the predefined identifier "id" used for?

  "The sets of assertions is denoted by /A/."

This should be "set of all", right?

  "Assertions are by default anonymous, but we can name them a
  predefined role id."

What does this mean?

  "That way assertions are only equal if they have identical members."

Surely that applies anyway?

In 1.3 there are actually two merging rules. If a map is a set of
assertions there is an implicit merging of equal assertions. The same
happens when maps are composed using set union.

In 1.4 the two basic operations are defined. Interestingly, since all
is defined in terms of roles in assertions, this is very similar to
the FM I proposed, if the model I used is changed to use the structure
I used for associations for *all* statements.

Regarding 2, are you sure that instances/subclassing belongs in the
core model? In my view this is more suitable for user-space
vocabulary.

/A^n/ is presumably the same as /A x A^n-1/ (ie, /A/s cartesian
product with itself n times)?

2.2 uses the terms "concept" and "object", but as far as I can tell
this is the first occurrence of these two terms.

In 2.2 there are no assertion types. Traversal of the assertions is
done purely in terms of role types, and no assertion type is tested
for.

Also, the operations in 2.2 would produce results for assertions of
the form (using LTM syntax for simplicity):

  whatever(a : superclass, b : subclass, c : superclass, d : subclass)

Surely there is a missing set of constraints here?

In "is-a<sub>m</sub><sup>0</sup>", what is the 0 doing there? Is it
because you're following 0 subclass steps? Isn't it better just to
lose that 0?

In 2.3 the list of operations provided is, interestingly, very nearly
the same as the one I sketch in my FM proposal. Yours is of course
much more detailed, but it's interesting that the operations seem to
be the same.

-- 
Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
GSM: +47 98 21 55 50                  <URL: http://www.garshol.priv.no >