Below are my understanding from READ and FIND commands in NATURAL. Please go through once and give your thoughts.
READ Physical - We use when we need to access huge data or entire data from the Adabas file. It reads directly from the Adabas blocks.
READ By ISN - We use when we need to access huge data or entire data from the Adabas file in order of ISN. Practically we can use it to read the records in the sequence it was stored. On first come first serve basis. It reads Adabas thru Address converter.
(Now if total number of ISNs get exhausted, will it use existing unused ISN numbers? If yes then the records will not be in FIFO basis)
READ Logical - We use when we need to access huge data or entire data from the Adabase file in order of any descriptor. It reads Adabas thru Inverted List.
FIND - We use when we need to access the records based any any specific criteria. We can use *NUMBER here to know the exact number of records fulfilling that criteria. It also access Adabas thru Inverted List.