The indexing of the entity records depends on the active
ACIS options when the model was saved. If they are indexed, the indexing is sequential starting at 0.
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-0 body $1 $2 $-1 $-1 #
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-25 point $-1 10 0 25 #
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In this example from a SAT file, "-0" and "-25" are sequence numbers. In the first line, "$1 $2" happen to be pointers to records (not shown) with sequence numbers "-1" and "-2", respectively.
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Even when the sequence numbers are not written to the file, they are implied by the order of the records in the file. Pointers to other records correspond to these implied sequence numbers. If sequence numbers are turned off, a record cannot be simply moved or removed from the save file, because this will create invalid index referencing when the file is restored.
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If sequence numbers are turned on, an entity may be deleted by simply removing its record from the save file. Any references to the removed record's index become
NULL pointers when the file is restored by
ACIS. With sequence numbers on, records may also be rearranged within the file.
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