Applying Haussler's formulation to trees we reach a general formula for a tree kernel between two trees t 1 and t 2 , namely where F is the set of all tree fragments, c 1 (f ) and c 2 (f ) return the counts for fragment f in trees t 1 and t 2 , respectively, and w(f ) assigns a weight to fragment f .
we can consider the kernel a weighted dot product over vectors of fragment counts.