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Direct Access File Organization and Retrieval

IP.com Disclosure Number: IPCOM000074931D
Original Publication Date: 1971-Jul-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 76K

Publishing Venue

IBM

Related People

Martin, PR: AUTHOR

Abstract

This program organizes a direct access data set and allows sequential, as well as random retrieval. Fig. 1 examines a file containing all keys to be loaded on the data set in sequence, as well as control cards describing pertinent information about the keys. The program condenses into a descriptor table, information describing the distribution of the keys on the data set and writes this table on another output data set for later use. During on-line accessing of the data set, Fig. 2 uses the descriptor table to convert the keys to relative block addresses (RBA).

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Direct Access File Organization and Retrieval

This program organizes a direct access data set and allows sequential, as well as random retrieval. Fig. 1 examines a file containing all keys to be loaded on the data set in sequence, as well as control cards describing pertinent information about the keys. The program condenses into a descriptor table, information describing the distribution of the keys on the data set and writes this table on another output data set for later use. During on-line accessing of the data set, Fig. 2 uses the descriptor table to convert the keys to relative block addresses (RBA).

Description of Fig. 1.

Step 1 reads parameters which include size and format of the keys, location of keys in the key file records, and the amount of core to be used for the descriptor table during on-line accessing.

Step 2 checks parameters for validity and supplies default values.

Step 3 initializes work areas including the descriptor table, which is built larger than its final required size.

Step 4 performs the loading function by writing the data record onto the data set.

Step 5 converts the key to a number according to the formula

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R(i) is the number of possible values the ith byte of the key may contain (e.g. R(i)=26 if the ith byte of all keys contains an alphabetic character). V(i) is the value of the ith key byte on a scale from 0 to R(i)-1. N is the key length in bytes.

Step 6 enters this converted key and its corresponding RBA into the table.

Step 7 checks to determine if all table space has been filled. If not, another key is read and entered.

Step 8 selects an entry from the table which is most nearly collinear with the adjacent entries.

Step 9 removes the selected entry, thus reducing the table by the size of one entry.

Step 10 checks to determine if the table has been reduced to its final required size....