[rules-users] facts hierarchy

[Giovanni Motta]

Hi all, i have a question concerning facts hierarchy, i'm looking for some
hint as i suppose the same problem could have been faced by someone on the
list.

I try to eplain with an example:

- Suppose to have a tree of facts, each object representing an UI widget.
   <root>
    <A id="1">
          <B />
    </A>
    <A id="2">
          <B />
    </A>
  </root>

- The individual elements A(1), B, A(2), B are mapped to facts, that are
inserted in a KnowledgeStatefulSession
- A rule exists that states that when an object A is selected, the B object
is automatically selected
- An event occurs that causes selection of node A(1)

The expected result is, obviously, that only the B element that is
descendant of A(1) must be automatically selected

I'm trying a way to express the 'descendant' relationship in LHS construct.
The rule will look like:

rule "A requires B"
when
$fact1: NodeFact(id == "A", selected == true)
$fact2: NodeFact(id == "B", selected == false,  this DESCENDANT-OF $fact1)
then
$fact2.setSelected(true);
end


What is, in your opinion, the best way to handle this situation? What should
replace the fake "DESCENDANT-OF" match?
Do i need to use a function that returns the list of descendant nodes of
$fact1 and then match $fact2 against that?
Will this be fast when dealing with large trees?

Any suggestion will be appreciated, thank you.
Giovanni
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