You need some comparable property in the singleton object that's monotonically increasing. Then you can have a rule like the following that must be of higher salience than the rules you want to protect from duplicate singletons. i.e.: rule "EnforceOneSingleton" when oldSingleton : Singleton( $id : id, $version : version ) newSingleton : Singleton( id == $id, version > $version) then System.out.println( "Retracting old Singleton " + oldSingleton.getId() + " version " + oldSingleton.getVersion()); retract( oldSingleton ); end --- On Mon, 8/17/09, Justin King <justin.matthew.king(a)gmail.com&gt; wrote: > From: Justin King <justin.matthew.king(a)gmail.com&gt; > Subject: [rules-users] Unique events / facts in working memory > To: "Rules Users List" <rules-users(a)lists.jboss.org&gt; > Date: Monday, August 17, 2009, 6:20 PM > I'm building an application that will > over time record changes in a certain component (not at any > set interval, could occur any time). The component can > possibly be uniquely identified via some kind of id. Is > there a way that when I insert an event / fact recording a > change of state in this component I can remove the previous > one, so as there is only ever one fact / event recording the > current state of the component. If the previous one existed > it may cause rules to fire which should not. > > > Cheers, > > Justin > > > -----Inline Attachment Follows----- > > _______________________________________________ > rules-users mailing list > rules-users(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-users > _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users