Graduate Thesis Or Dissertation
 

The evaluation of data file access methods for an on-line information system

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  • It is necessary to evaluate and compare the characteristics of various methods of accessing data-files in order to utilize economically both the hardware and the software (Space and Time) supported by the digital on-line system. The purpose of this paper is to describe and evaluate the structure and use of four conventional methods of file organization: Sequential File, Indexed Sequential File, Partitioned File, and Direct File. Special attention is given to the Direct File, which possesses the fastest accessing time. Five selected Hash Coding Techniques, each associated with three methods of handling redundant keys, are simulated and examined with the use of a selected data model of 1024 random United States names, and the resulting "average number of search per record retrieval" are compared with their corresponding theoretical values. As Hash 1 has offered the best results, it has been used to evaluate the organization of the Direct File, and to compare this organization with that of the other files. The CDC-3300 system hardware parameter, control cycle time, the internal core storage, and the auxiliary storage parameters are introduced. From these values and the average number of searches per record retrieval, an expression of logical record file size, or loading factor is developed. The file size, or loading factor varies for different methods of file structure and accessing, (based upon the selected testing program). The system characteristics consisting of the average throughput per record retrieval, achievable-throughput-rate capability and user operating cost per call (unit cost) are evaluated and compared. The file system uses the full name of the record and a fixed length numerical key. Two common internal searches, Linear search and Binary search, are evaluated and compared as the preliminary work of this investigation, as shown in Appendix B.
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