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

[Simon Chen]

On Mon, Feb 21, 2011 at 4:03 PM, Ansgar Konermann
<ansgar.konermann at googlemail.com> wrote:
> On 21.02.2011 04:11, Mark Proctor wrote:
>> On 21/02/2011 03:03, Simon Chen wrote:
>>
>>> 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?
>>>
>> InsertLogical operates on equality mode, that is determined by the
>> pojo's equals() method implementation. If an object already exists that
>> is equal, it will use that and the justification counter for that
>> existing object is increased.
>>
>> Mark
>>
>>>> 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?
>>>
>
> Easy case (insertLogical does not introduce duplicate objects):
>
> when
>      edge(a, b)
>      reach(b, c)
> then
>      insertLogical( reach(a,c) )
>
>
> If insertLogical did introduce duplicate objects, we'd need this:
>
> when
>      exists edge(a, b)
>      exists reach(b, c)
> then
>      insertLogical( reach(a,c) )

I don't see why this would prevent the duplicate objects... Let's say,
the first rule inserted reach(a1,c1) as a duplicate, given edge(a1,b1)
and reach(b1,c1). The same duplicate reachable(a1,c1) would be
inserted by the second rule as well, right? I don't see why duplicates
are prevented by the second rule.

Again, I'm not a language person, so please educate me...

Thanks.
-Simon



>
>
> Kind regards
>
> Ansgar
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