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

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(a)googlemail.com&gt;   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) )

Kind regards Ansgar _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users