What I had is a very simplified version of how calculating transitive closure could go wrong...
Let's say we have two rules: rule 1 when link(a,b) then insertLogical(new reachable(a,b)) rule 2 when link(a,b) reachable(b,c) then insertLogical(new reachable(a,c)) Let's say, I have link(a,b), link(b,c), link(b,a), link(c,b). So, we'll have reachable(a,b), reachable(b,c), reachable(a,c), etc. But, after I retract link(a,b) and link(b,a), guess what, reachable(c,a) still exists! This doesn't sound right to me. But in Drools, this is possible, because we have: reachable(c,a) <- link(c,b), reachable(b,a) reachable(b,a) <- link(b,c), reachable(c,a) The problem here is that we actually inserted reachable(b,a) multiple times: first supported by link(b,a) and rule 1, and secondly by link(b,c) and reachable(c,a) and rule 2. When reachable(b,a) was inserted the second time, link(b,c) and reachable(c,a) become the additional supporting condition - maintained by the truth maintenance system. So, even if link(b,a) is retracted, reachable(b,a) still exists further supporting reachable(c,a). Is it clearer? Thanks. -Simon 2011/3/7 Edson Tirelli <[email protected]>: > > Simon, > The behavior seems correct to me as B is justified by either A or C (or > both). Of course, from the initial state, A is required for C to first > exist, but once it starts to exist, your rules say that B and C justify each > other and so both remain in memory. > This is design as intended, but do you think that is wrong? > Edson > > 2011/3/7 Simon Chen <[email protected]> >> >> Hi all, >> >> An interesting finding: >> >> I have three simple rules: >> rule "A2B" >> when >> A() >> then >> insertLogical(new B()); >> end >> rule "B2C" >> when >> B() >> then >> insertLogical(new C()); >> end >> rule "C2B" >> when >> C() >> then >> insertLogical(new B()); >> end >> >> Basically, once we have an A(), we'll logically insert a B(). Once we >> have a B(), we'll logically insert a C(). Once we have a C(), we'll >> logically insert a B(). >> >> So, I first insert an A(), print all the objects. Retract A(), and >> print all the objects. Here's what I got: >> com.sample.B@42 >> com.sample.C@43 >> com.sample.A@548997d1 >> after retract! >> com.sample.B@42 >> com.sample.C@43 >> >> So, B() and C(), which should be logically depend on A(), somehow are >> not retracted. The problem I see is the truth maintenance system allow >> B() and C() to depend on each other, thus not affected by losing A(). >> >> Is this a bug or my bad usage? >> >> Thanks. >> -Simon >> _______________________________________________ >> rules-users mailing list >> [email protected] >> https://lists.jboss.org/mailman/listinfo/rules-users > > > > -- > Edson Tirelli > JBoss Drools Core Development > JBoss by Red Hat @ www.jboss.com > > _______________________________________________ > rules-users mailing list > [email protected] > https://lists.jboss.org/mailman/listinfo/rules-users > > _______________________________________________ rules-users mailing list [email protected] https://lists.jboss.org/mailman/listinfo/rules-users
