[rules-users] Logical insert and cyclic rules dependences

[Wolfgang Laun]

Inferring cause from effect is a logical error.

In your example, one can see that there are two meta-levels. One deals
with physical entities (fire, bell) and the other one with human
sentiments ("being alarmed"). There can be interactions between
levels, but they should be well-defined. (E.g.: I can be alarmed for
many reasons, but this does not give me the right to ring the bell,
but the fire alarm bell ringing is a good reason for me being
agitated.)

You can trip any logic system with such "unclean" reasoning. I'm sure
you know the Barber paradox.

-W


On 03/07/2012, zephyr <ls262570 at students.mimuw.edu.pl> wrote:
> With
>
> "a" is the only inserted fact
>
> a->b->c->d->b
>
> now b,c,d are logically added, b's ref cnt is 2
>
> Fact b is NOT inserted again, (it's ref cnt is increased) and its more or
> less what i wanted.
>
> The problem is, when i remove fact a, b's ref cnt goes to 1, so it stays.
>
> So b,c,d stay in fact memory because they support each other, even though
> all stated facts that support them (fact a) were already removed.
>
> Still no loop in rule firing, but i have junk in fact memory that can later
> cause rules i don't want to fire fire.
>
> Some less abstract example
>
> see fire -> ring a bell
> ring a bell -> bell rings
> bell rings -> be alarmed
> be alarmed -> there is alarm
> there is alarm -> bell rings
>
> When anyone sees fire i want all stuff to be in fact memory, but when all
> decide they see no fire anymore and ring a bell disappears i would like
> this
> alarm cycle that was logically inserted because of see fire to disappear.
>
> (Maybe not the best example as here you should take some action to stop
> ringing the bell, nad use ear not deduction to hear ringing, but im writing
> a "thinking modelling system" and i haven't thought of better non abstract
> example yet, though my system will be abstract and i do think there are
> less
> stupid use cases when you would not like "unsupported logical circles" to
> stay)
>
>
> laune wrote
>>
>> On 03/07/2012, zephyr &lt;ls262570 at .edu&gt; wrote:
>>> In this case yes, but generally those dependences can be much more
>>> complicated and this example is the simplest ilustration of the problem.
>>>
>>> It can also be
>>>
>>> a-> b ->c ->d ->b
>>
>>
>> In this scenario, Fact b would not be inserted again, because thruth
>> maintenance
>> always uses equality, irrespective of the runtime configuration
>> identity/equality.
>>
>> Make sure to override equals and hashCode correctly, go by the book,
>>
>> -W
>>
>>
>>>
>>> (that makes b,c,d equivalent, but is little less trivial to detect)
>>>
>>> or more complicated
>>> a->b
>>> b->c
>>> c and d -> b
>>> d nad a are facts, then a is removed
>>> c and b are not eqivalent, but still support each other while there is
>>> fact
>>> d
>>> etc.
>>>
>>> I just want logical facts that are not connected by any rule path with
>>> inserted facts and only stay because of logical fact cycles to disapear.
>>>
>>> Im writing a system that takes user generated dependences as input and
>>> its
>>> main goal is to deal with different consequences, i thought drools might
>>> be
>>> a right tool to base this system on, this didnt work so i wonder is it a
>>> common problem and is there an easy way to deal with it (or some way to
>>> change drools to work like this).
>>>
>>> --
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