Described is a technology in which a finite state machine-based method segments original sequential data into high level units. Segments with similar sub-sequences are treated as the same unit. In general, the finite state machine indentifies sub-sequences in the sequential data that have similar tree-like microstructures. One described finite state machine operates by entering a path state when an input is a path command corresponding to a non-leaf node; the state machine remains in the path state until another command comprises an action command corresponding to a leaf node, whereby it outputs an action unit, or until the other command comprises a path command that is not the parent or the sibling of a next command, whereby a browsing unit is output. Also described is aggregating sub-sequences of a same unit to produce an access structure corresponding to the unit.