The files are grouped into {HEAD ~ at least one set} of {TAIL ~ files}, where the files in the set are accessed together more than a predetermined number of times in the trace 
The files are grouped into { HEAD ~ at least one set } of { TAIL ~ files } , where the files in the set are accessed together more than a predetermined number of times in the trace
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH