Following is a demo of bi-directional transitive closure on a
muti-rooted tree using dbd. It represents the following boss/employee
hierarchy:

john
bob
jack
bill

mary
sue
jack
bill

(new 'john 'person)
(new 'mary 'person)
(new 'bob 'person)
(new 'sue 'person)
(new 'jack 'person)
(new 'bill 'person)

(new 'boss 'verb)
(new 'employee 'verb)

(set boss leads up)
(set employee leads down)

(set boss reciprocal employee)
(set employee reciprocal boss)

(; Note setWRR automatically creates reciprocal relationship)
(setWRR john employee bob)
(setWRR bob employee jack)
(setWRR bob employee bill)

(setWRR mary employee sue)
(setWRR sue employee jack)
(setWRR sue employee bill)

(; Get john's employees recursively)
(; Gets bob, jack, bill)
(getRel john employee *)

(; Get mary's employees recursively)
(; Gets sue, jack, bill)
(getRel mary employee *)

(; Get jack's bosses recursively)
(; Gets bob, john, sue, mary)
(getRel jack boss *)

(; Get bill's bosses recursively)
(; Gets bob, john, sue, mary)
(getRel bill boss *)


For more examples, see www.dbfordummies.com