21. A method according to claim 15 , further comprising: performing the heuristic search as an A* search comprising a path from an initial node to a goal node through the set of zone hypotheses, wherein the initial node comprises a current zone hypothesis and the goal node comprises a partition of the zone hypotheses set comprising a subset of disjoint sub-zone hypotheses.
15. A computer-implemented method for retrieving a digital image through document image decomposition, comprising: retrieving a stored digital image from a database of stored documents; extracting generic visual features from the stored digital image; grouping the generic visual features into a primitive layer comprising a plurality of word-graphs that each comprise one of words and visualized features; grouping the one or more of the words into a layout layer comprising a plurality of zone hypotheses that each comprise one or more of the words; expressing causal dependencies between the word-graphs in the primitive layer and the zone hypotheses in the layout layer through zone models that each comprise a joint probability defining a pair of probabilistic models generated through a learned binary edge classifier; expressing each pair of probabilistic models as an optimal set selection problem comprising a set of cost functions and constraints; evaluating the optimal set selection problem through a heuristic search of the cost functions and constraints and providing a non-overlapping optimal set of the zone hypotheses that characterize the stored digital image.