[rules-users] Noob question: graph searching, query, root node for a given node

[Borris]

I'm after a quick bit of help on how to do something that I think should be
easy but I can't work out how.

I have a Java-side class that essentially is something like

declare Datum
    description: String
    broader: List <Datum>
    narrower: List <Datum>
end

These are arranged in a graph. Root nodes have no items in their broader
list. I want a query that takes a datum and yields the root nodes for that
datum. I think this should look something like

query rootDatumsFor( Datum datum, Datum result )
    not Datum() from $datum.broader
    or
    rootDatumsFor( $datum.broader, $result )
end

but I then get confused. When there are no broader items, I am unclear how
to assign $datum to $result. And I'm not convinced I'm doing the recursion
correctly either.

If an experienced Drools author could spend a minute and show me how to do
this sensibly, I would be very grateful.






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