[rules-users] To accumulate or not to accumulate

Hello, I am trying to implement rules handling "Sentence", "ManualAnnotation" objects (imagine someone highligthing words of the document). Basically "Sentence" objects have "start" and "end" positions (fields) into the text of a document, and they are Comparable according to their location into the document. I need to write rules using the notion "window of consecutive sentences". Basically I am not very interested by those "SentenceWindow" objects, I just need them to define a kind of proximity between "ManualAnnotation" objects. What I eventually need in the "when" of my rule is something like: when ... maybe something creating the windows a1 : ManualAnnotation () a2 : ManualAnnotation (this != a1) SentenceWindow (this includes a1, this includes a2) then ... do something with a1 and a2 since they are "close" to each other end As I don't know the "internals" of Drools, I would like to have your opinion about what the best "idiom": * create all SentenceWindow objects and insert them in the working memory, then write rules against all the facts (SentenceWindow and ManualAnnotation) * implement an accumulator that will create a list of SentenceWindow object The first option could look like: |||rule "Create sentence windows" when # find 3 consecutive sentences s1 : Sentence() s2 : Sentence(this > s1) s3 : Sentence(this > s2) not Sentence(this != s2 && > s1 && < s3) then SentenceWindow swindow = new SentenceWindow(); swindow.setStart(s1.getStart()); swindow.setTheend(s3.getEnd()); insert(swindow); end| ... Then use the first rule "as is". The accumulator option could look like (I am not really sure the syntax is correct) : when *$result : ArrayList() from accumulate ( $s: Sentence(), buildwindows($s))* a1 : ManualAnnotation () a2 : ManualAnnotation (this != a1) *SentenceWindows (this includes a1, this includes a2) **from $result* then ... do something with a1 and a2 since they are "close" to each other end Is it possible to decide if one way is best than the other? And one last question: it is possible to "parametrize" an accumulator (in order to provide the number of sentences that should be put in the windows)? I mean something like: when $result : ArrayList() from accumulate ( $s: Sentence(), *buildwindows(3,* $s)) Thanks in advance for you insights, Best regards, Bruno.