The hierarchical structuring is an important way of organizing many kinds of data. It groups the least rapidly changing variables (e.g., header data), then the next-most rapidly changing information, etc. For example, a hydrographic section might look like
leg year /[lowest (0) level]/ month station lat /[level 1]/ lon date press temp sal /[level 2]/ o2 sigth
A current meter mooring might have
mooring_id lat lon /[level 0]/ nominal_depth start_time end_time time u /[level 1]/ v temp
Often one scans the lower level information first to pick out the desired station or mooring and then retrieves the information only for that subset of the data base.