Re: assert vs instance-of and other questions

On Jan 13, 2006, at 7:46 AM, Kotaro Funakoshi wrote:

>> STELLA(22): (all-facts-of george)
>> (|P|(ISA GEORGE MONKEY) |P?|(MONKEY GEORGE) |P?|(INSTANCE-OF  
>> GEORGE MONKEY))
>> STELLA(23):
>>
>> The `all-facts-of' shows that `(MONKEY GEORGE)' was inferred via
>> forward-inference.
>
> You mean |P?| indicates a forward-inference proposition, right?
> Now another mystery is resolved :-)

Only indirectly.

The forward inference is indicated by the appearance in the list
returned by ALL-FACTS-OF, which does not do any backward inference.
So all it shows are those facts which were asserted or inferred
by using forward chaining inference.

The real meaning of |P?| is that the proposition is UNKNOWN.
But since the proposition really is true, this is a bit misleading.
The explanation requires knowing a bit about some of the details
of how PowerLoom reasons and manages its propositions.
A particular module contains only the information that has been
asserted into it.  Any inferred information is actually stored
in a separate "inference world" associated with that module.
Inferred facts and propositions are stored in that separate
world where they are known to be true.  But since the propositions
returned by ALL-FACTS-OF are printed in the base module, where
the truth value of the propositions is unknown, they print as
unknown.  That is why the marking with P? is only an indirect
indicator.  In fact if you use CONCEIVE rather than ASSERT,
you will also see an unknown proposition, since that is what
CONCEIVE creates.

Queries.  All queries made are done in the inference world so they will
properly see the inferred information.

Also, if you ever use default reasoning, then propositions that
are known by default will print with a lowercase "p" instead of "P".

By the way, you can turn off the printing of tags by setting
the variable *printreadably?* to false.  In Java it would be
called Stella.$PRINTREADABLYp$.