In this particular case you can do $p1:person (name=="Alice") $p3:person (name=="David", this after[0,1] $p1) not person (name != "Bob", this after[0,1] $p1 && before[0,1] $p3 ) A more general approach should be possible by monitoring states rather than event sequences, especially if you process events in real time. 1) Alice => state := A 2a) David => OK 2b) Bob => state := AB 2c) Edward => state := _ And so on. -W On 20 July 2011 22:21, Edward Johnson < ejohnson(a)coderyte.com > wrote: How do you do rules that are a sequence of events where some of them are optional? Example: Alert if DAVID enters a room after ALICE or after ALICE and BOB If it were a string, this is roughly equivalant to the regex /ALICE( BOB)? DAVID/ So: Alice then David => alert Alice then Bob then David => alert Alice then Charles then David => no alert I could write this as two rules but as the rules get more complex it could by hard to manage the resulting combatorial explosion. Here it is as two rules: Rule 1: $p1:person (name=="Alice") $p2:person (name=="David", this after[0,1] $p1) Rule 2: $p1:person (name=="Alice") $p2:person (name=="Bob", this after[0,1] $p1) $p3:person (name=="David", this after[0,1] $p2) _______________________________________________ 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