15. The system of claim 14 , wherein the design module is further configured to: pack the plurality of elements of the tree-structured data, including the first set of elements and the second set of elements and the meta-data levels associated therewith, into a plurality of leaf nodes of the index structure; merge the plurality of leaf nodes of the index structure into a plurality of non-leaf nodes of the index structure until a root non-leaf node is generated; and associate the plurality of non-leaf nodes of the index structure with the explicit meta-data levels of the packed first set of elements.
16. The system of claim 15 , wherein the design module is further configured to assign a non-leaf node a range of explicit meta-data levels, the range of explicit meta-data levels including a low explicit meta-data level and a high explicit meta-data level of at least one descendent non-leaf node.