On-Line File Update and Maintenance

Abstract

The principal reason for on-line, real-time update of a file is to serve the operational needs of those systems in which the Update transaction must be usable in the file within a very short time from its declaration. Cost comparisons between on-line versus batched updating are deceptive because of the manner in which one may choose to account for such fixed costs as the DASD, terminals, and software. Therefore, the decision should be qualitatively based upon a requirement for timely updates, unless the hardware and software accounting is so clear-cut as to enable a cost comparison. For example, if the software were supplied with the equipment, and all equipment were charged strictly on a time, type, and capacity basis (i.e., broken down by equipment type and quantity of direct access storage), then one could readily compare costs. Other than in this kind of clear-cut situation, the difficulty arises in apportioning the share of hardware cost to be carried by the update functions, because, notwithstanding on-line update, the same DASD and terminal costs would have to be sustained in support of retrieval functions. Software design and implementation costs, however, would be higher, and these should be accounted. A single update can be executed typically in terms of time from a few tens to hundreds of milliseconds of processing time, depending on equipment type.