[sc34wg3] Reference Model to SAM - Mapping Issues and Thoughts

[Graham Moore]

Hi all,=20

I decided to pick up this issue from Steves posting as I agree with him =
that it is the perhaps the most fundamental aspect of a multi-part =
standard. If the parts are incoherent as a whole then semantic =
interchange is doomed and we have a big mess.

I would just like to lay out what I feel the issues we face in defining =
this SAM RM mapping. Some of these things are done or in place already =
but it feels good to have a complete (maybe) list and even better if =
some things are ticked off.

1. PSI definitions for all SAM constructs that can be represented in the =
RM. This allows an up and down translate with no loss of information =
when viewing the SAM after migrating it down to the rm then back up.

2. A definition of how each SAM construct 'looks' as a RM subgraph. =
Including use of PSI structures. With this though perhaps a place to do =
the Mapping is in the SAM itself alongside each information item. This =
then sets a standard way that any models defined in terms of the RM =
metamodel must for each 'item' define its relationship to the RM?

3. This issue I think is the biggy and is the issue that has troubled me =
for many months. The RM, simply put, has more nodes than the SAM. It has =
more things although less types. The SAM actively hides some nodes that =
a RM view exposes. Thus taking a RM model and viewing it as the SAM =
means that some things are NOT addressable. My feeling is that this is =
exactly what should be happening. We build levels of abstractions for =
different purposes - in this case to make the most prominent and =
important part of our intellectual thinking available in a easy to =
understand and useful form. The open question and the one to which I =
seek comment is - 'Is it ok for the SAM to lose some nodes such that =
some RM parts that were addressable are no longer so - even if the SAM =
is translated back into a RM representation?=20

Here is an example - around the area of subjectIndicators the RM has =
many more nodes to express subjectInidcatormess. If someone at the RM =
level makes an assertion about one of these nodes and then translates =
that into a SAM the SAM IS NOT able to maintain that information and it =
will be lost. Its becuase there are nodes in the RM that have no =
identifiable equivalent in the SAM.

This means that :

3.1 SAM -> RM -> SAM (is loss-less)
3.2 RM -> SAM -> RM (is loss-less in cases where assertions arent made =
about items that have no identifiable node in the SAM.)

I think this is ok and if its ok with everyone else then I dont really =
see that we have a problem.

The implication, if the SAM must have a mechanism for accessing the =
underlying RM with ALL nodes present, is that ALL implementations of all =
Topic Map Models (SAM or otherwise) must maintain all relevant RM nodes =
and thus be implemented in terms of RM structures. Yikes!

I hope this helps the mapping process as it is a critical part of this =
activity.

cheers

Graham

Graham Moore
vp rd empolis
gdm@empolis.co.uk



=20

_____________________________________________________________________
This=20message=20has=20been=20checked=20for=20all=20known=20viruses=20by=20=
the=20MessageLabs=20Virus=20Scanning=20Service.