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Dynamically Modifiable File Access Method

IP.com Disclosure Number: IPCOM000077990D
Original Publication Date: 1972-Oct-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Mingot, C: AUTHOR

Abstract

This method permits changes to be made in a logical file organization (and consequently its access means) without changing its physical organization. Such a result is achieved by two special tables which provide correspondence between record addresses and search arguments (keys), and define the record structure, respectively.

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Dynamically Modifiable File Access Method

This method permits changes to be made in a logical file organization (and consequently its access means) without changing its physical organization. Such a result is achieved by two special tables which provide correspondence between record addresses and search arguments (keys), and define the record structure, respectively.

Fig. 1 shows, as an example, the structure of a record in a staff file. Each record relates to one individual and contains data such as his name, the date he joined the Company, his employee serial number, etc. A record is written in a physical block comprised of an unbroken sequence of positions on a disk track, and can be retrieved by a key. When the file is initialized, the length,of the records, the length of the key and the maximum number of records are defined.

A first table (Fig. 2) contains the physical addresses of the blocks reserved for the records. Each address consists of three numbers (cylinder, head, record). When a record (whether complete or incomplete) is written in a block, the key is written into the table, in front of the address block. When a record is removed from the file, the key (but not the address) is deleted.

A second table (Fig. 3) defines the structure of the records. This structure, at a given step of the operation, is identical for all records. Each data is identified by a label. The table shows, for each data, the label, the Position of the first byte of the field that contains the data, and the length of the field. Labels may be assigned to complex data occupyi...