27. The method of claim 26 , wherein the generating a score for a structure having an aggregate comprises calculating an overall score for the aggregate as a match for the search expression by calculating c 1 *D+c 2 *Δ, where D is a density of the search expression on the aggregate, Δ is a distribution score for the search expression on the aggregate, and c 1 and c 2 are positive real numbers such that c 1 +c 2 ≦1.
26. The method of claim 25 , wherein the generating of a score for a structure having an aggregate comprises calculating (a) a deviation score of the search expression, and (b) for each sub-expression of the search expression, a density and a relevance center of the sub-expression, for the aggregate, the calculating being performed using at least relevance geometry of the aggregate, one or more deviation scores of the search expression of each child of the aggregate, and a density of each sub-expression of the search expression for each child of the aggregate.