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Rule systems, because of their declarative focus, are concerned with bits of knowledge<= /em>. Rule systems come across this knowledge over time, and the details o= f this knowledge is subject to frequent change. The rule system typically= uses this knowledge to make complex decisions.
Over time, a thing which was once true might cease to be true. The rule= system can be trained to acknowledge this change in conditions. As the kn= owledge in the system changes, it affects decisions that system makes. Som= etimes, when the system decides that a bit of knowledge is no longer releva= nt or useful, that bit of knowledge is forgotten, cleared from the system's= memory.
In Drools there are operations for becoming aware of a fact, purging a f= act, or modifying a known fact. There are ways to use these operations thr= ough Drools' runtime API, and ways to encapsulate these operations into DRL= files. But they are summed up here:
Remember a bit of knowledge or commit it to memory.
Example: Remember that weather is rainy today.
Forget a bit of knowledge or remove it from your memory.
Example: Forget the weather from last Wednesday =E2=80=94 it isn't impo= rtant anymore.
Alter a bit of knowledge about something when the conditions change.
Example: Acknowledge when the rain ends and the weather turns sunny and= remember from that point on that the weather outside is pleasant.
Knowledge in a Rule Engine is collected into the Working Memory. Knowledge is asserted, retracted a= nd modified within the working memory and the rules are evaluated to determ= ine what actions, if any, should be taken over the course of the rules' exe= cution.------=_Part_1150_266767537.1369214516473--