4. The method according to claim 1 , further comprising retrieving one of the objects, wherein the retrieving comprises acquiring from the top level sub-tree link to a mid-level sub-tree, acquiring from the mid- level sub-tree a link to a low level sub-tree, and retrieving the object from the low level sub-tree.
4. The method according to claim 1 , further comprising retrieving one of the objects, wherein the retrieving comprises acquiring from the top level sub-tree link to a mid-level sub-tree, acquiring from the mid- level sub-tree a link to a low level sub-tree, and retrieving the object from the low level sub-tree. 5. The method according to claim 4 , further comprising processing information of one of the sub-trees to generate a unique identifier of the sub-tree, wherein the retrieving is responsive to identifier information, wherein the retrieving comprises retrieving the object in response to a result of at least one comparison of the identifier information to the unique identifier of at least one sub-tree.