The Shen MRS

[Antti Ylikoski]

Hi all:

I have learned that there are there plans to devise a MRS like, but

better, automated reasoning system with Shen.

My own interest in the MRS was twofold.  I wanted to improve on my

professional competence with AI software "by getting my hands wet"

with some working software.  I also wanted to be able to create

something working and useful to make for myself a (pretty modest,

admittedly) name in the local AI world.

Taking part in the building of the Shen MRS fulfills those two goals

much better than converting the MRS into the Common LISP.

I also shall get the LPC and the TBoS and possibly start working on a

software environment for the Shen program verification.

Therefore, I shall start writing a series of entries concerning the

MRS system here, to aid in designing the Shen MRS, and I would love to

take part in building the Shen MRS in the future, for the above

mentioned two motivations.

yours, Dr Antti Ylikoski

Helsinki, Finland

[Antti Ylikoski]

The main functionality of the MRS system works as follows.

There is there a function called the (scheduler), which operates to a

large extent in the same manner as the scheduler in timesharing

mainframe systems.

There is there a list of tasks to execute, they are in the variable

agenda, they are a list of S-expressions which can be EVALed.

At every individual step, the scheduler finds the next -- i. e. the

highest priority -- task to execute, from the task list agenda.

Then, the scheduler EVALs (or maybe FUNCALLs) the next task.

New tasks may be added to the agenda, tasks may be removed from the

agenda, the agenda may be rearranged, the EVAL step of course may do

anything at all to the state of the MRS system.

Then, the step repeats.

Following is a simplified scheduler function:

------------------------------------------------------------

(defun scheduler ()

  (do ((task (next) (next))) ; Var init repeat

      ((null task) nil)            ; End condition: task is NIL

    (eval task)))                  ; Execute current task

------------------------------------------------------------

And following is a simplified (next) function:

------------------------------------------------------------

(defvar agenda nil) ; List of S-expressions to execute

(defun next ()

  (declare (special agenda))

  (multiple-value-bind (task agenda) (find-next-task agenda))

  task)

------------------------------------------------------------

When the function (find-next-task ...) determines the next task, there

may be there in the knowledge base meta rules as to which task is

given which priority, or something such as that.

For example, one may specify that tasks concerning immediate alarms as

to the machine to be diagnosed, are given higher priority than

ordinary reasoning steps.

yours, Dr Antti Ylikoski

Helsinki, Finland