Re: How do RDF and Formal Logic fit together?

Sandro Hawke wrote:
> 
> We want to be
> able to have semantic web pages be little programs (like HTML pages
> with javascript, but cleaner).  We want to be able to validate a date
> field or do currency conversion, etc, etc.
> 

Just to hook on to these points. 

The Semantic Web should be machine and human readable. The way I tackle
this aspect in Notion System is that starting from the point that the
human user is the master of information creation the system must make
something from it so it can work with it. 
For things that are supposed to represent periods of time (like dates,
indications of centuries, etc) it uses a service called DatExpert
(Sandro: one of the your "little programs") that analyses the input data
and transforms it into an agreed standard period exchange format. For
DatExpert this is a 64 bit integer with the 0 somewhere 15 billion years
ago (a bit beyond the Big Bang) and capable of going 277 billion years
in the future. 
Nothing new with this? Yes there are a few things.

1 the used service has extended knowledge about various calendars and
their specific aspects like e.g. the geographical area and time period
in which these calendars are used.

2 it might use other information in the semantic network in order to
figure out start and end dates from events or statuses that are used as
dates (second world war, II Dynasty of Chang).

3 the obtained information is added in two separate properties (derived
start "date" and derived end "date") to the original information. For
these derived dates again some properties are added like the quality of
the conversion, nodes used, service used and a timestamp. This info is
for machine exploitation only (but human users can see it if they really
want to). Why two dates? Well every date indicates a period over time.
Whether the period is to be considered as a point in time only depends
on the resolution of the view you have on it (year, second, etc) it
doesn't depend on the period itself. This allows you to use upper and
lower limits as necessary.

4 When representing dates afterwards to a human user a "displaying
service" might either represent the original information and / or use
the DatExpert service to reconvert this in the form the particular user
is used to see dates.

In resume:
Original date slots (human created) may contain any kind of value
(traditional date forms up to things like "Easter 1960" or "l'an mil
trois cent vingt trois ap. J.C."), derived date slots contain machine
processable forms (using the French "NumberConversion" service for the
last example). Historians, geologists and astronomers can use dates as
they are used to also (do you see the resolution of the 4 time scales?)
The knowledge (logic) about dates is a combination of facts (e.g. about
calendars) within the network and rules how to use these facts.

More important even is the fact that if a conversion service is not
capable of doing a reliable conversion at time T0 it might be that the
user made a mistake (active interaction might correct this) but also
that the network lacked some facts. But at time T1 this conversion might
succeed (the semantic web is constantly growing). Should we bother the
user with this? Personally I would not like that.

Accepting original data not confirming the rules is really important. A
real life experience: In France an editor published during a few years
books with a wrong ISBN (wrong according to the rules applied to
ISBN's). The "ISBN" service of Notion System did tell me the ISBN was
wrong but as the books are known under these numbers they must be
accepted.

The use of these kinds of services in the semantic web will be extremely
useful in all aspects. Allowing to bridge non acceptable constraints to
human users (but helping them to correct possible errors) and still
providing functionality as good as possible and capable of exploiting
new knowledge as it is added to the sw.

For these real life situations I conclude for the semantic web that:
- applying strict rules (constraints) at all time might lead to
unacceptable situations (ISBN example)
- services (like the ones mentioned) must be trusted
- derived information (in particular the ones with a low reliability)
should be resubmitted periodically in order to improve the quality of
the information.
- human users remain for the next few years the masters of information
creation, machines (applications, services) should be come the masters
of transformation for human exploitation.

Ronald Poell