Updating a master file—yet one more time

For several years I have been teaching a file updating algorithm which is essentially the same as that in Dwyer's admirable paper [1]. There is one unjustified objection to the algorithm that perceptive students and people with batch processing experience almost invariably raise and which is not addressed by Dwyer. The objection is based on a situation which arises in a batch processing environment with several users, where key-ordered sequential update is used.

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