[rules-users] unsolved myth regarding transitive closure using insertlogical...

[Simon Chen]

On Sun, Feb 20, 2011 at 8:20 PM, Ansgar Konermann
<ansgar.konermann at googlemail.com> wrote:
> On 19.02.2011 16:01, Simon Chen wrote:
>> The example you gave seems to be the one-hop case. For the two-hop
>> case, we need something like this
>>
>> when
>>     edge(a, b), reach(b, c), not exists reach(a, c)
>> then
>>     insertLogical( reach(a,c) )
>>
>> So, where do you put your logical around? It should include both
>> edge(a,b) and reach(b,c), right?
>>
>> Another thought, can we have something like
>> testExistsAndInsertLogical() to replace insertLogical()? But this may
>> be buggy, as the conditions are all met, so the rule actually fired...
>>
> Hi,
>
> from my experience, insertLogical does exactly what
> testExistsAndInsertLogical would suggest. If the same object is already
> in the working memory, it keeps this object and does not insert another
> instance. This behaviour is not stated explicitly in the documentation,
> but I did a learning test a few weeks ago and IIRC it clearly showed
> this behaviour (at least for 5.0.1). -- I consider this behaviour a
> feature and would like it to be kept this way.

I am using Drools 5.1.1, and I don't think insertLogical prevents
duplicates automatically. This also boils down to the question of how
Drools decides whether two objects are indeed the same. For strings
and integers, it is straightforward, but not much so for complex
objects. Is there a way to pass in a comparison function?

>
> With this, all which is necessary to implement transitive closure is to
> remove the contradicting part of the precondition to avoid oscillation.
> If it turns out that insertLogical does not perform a "does fact already
> exist" check and thus might potentially insert duplicates, put exists( )
> around the two preconditions and also use "exists( reach(x,y) )" to
> check whether y is reachable from x.

I don't quite follow. Can you elaborate with an actual rule?

Thanks!
-Simon

>
> Kind regards
>
> Ansgar
> _______________________________________________
> rules-users mailing list
> rules-users at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>