Re: basic question

Kaveh Kardan <[email protected]> writes:

> Do the "facts" of the system have to be CLOS classes or templates?

Facts can be both CLOS instances and Lisa templates.  I guess that
templates are better for simple facts or "legacy" rules (e.g. when
porting from CLIPS/JESS), and CLOS instances for more complex cases.


> Is it possible to have LISA do inference over facts expressed as
> thunks or arbitrary lisp expressions?

Not directly, but you could created CLOS classes or Lisa templates
with slots containing the required thunks, and use test patterns for
matching if necessary.


> For example, I have a movie scene, and I am developing a system for
> automatically placing the camera to best shoot the scene.  I would
> like to be able to express rules such as the following:
>
> (defrule rule-1 (:cf 0.8)
>    (is-first-shot-of *scene*)
>    =>
>    (make-establishing-shot *scene*))

What is is-first-shot-of?  A function?  If so, you could use something
like (untested, no pun intended):

(defrule rule-1 (:cf 0.8)
  (test (is-first-shot-of *scene*))
  =>
  (make-establishing-shot *scene*))


> Also, how would one best express things such as the following as a rule?
>
>    (let ((actor-1 (current-subject *scene*))
> 	(actor-2 (non-current-subject *scene*)))
>      (if (> (viewer-identification-with actor-1)
> 	   (viewer-identification-with actor-2))
> 	(make-closeup-shot actor-1)
> 	(make-over-the-shoulder-shot actor-1)))

You may express the LET bindings with object/template matching, using
variables and tests if necessary.


> pointers to articles or texts with a practical bent would be
> appreciated.

See:

  LISA and rule-based programming in Common Lisp
  http://www.paoloamoroso.it/log/050827.html


Paolo
-- 
Lisp Propulsion Laboratory log - http://www.paoloamoroso.it/log

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