Browse Prior Art Database

Back Link Method of Storing Records

IP.com Disclosure Number: IPCOM000073572D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Ganguly, AK: AUTHOR [+2]

Abstract

Described is a back-link method of storing records in the independent overflow area of Indexed Sequential Access Method (ISAM). Assuming N primary tracks of data, the new records which belong to the ith primary track and are to be added to the overflow area are denoted R(i1), R(i2)..., which is also the chronological order in which the overflow records are added. As records belonging to all the primary tracks are added in the same overflow area, in between R(ij) and R(ij+1) , records belonging to other primary tracks may be stored.

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Back Link Method of Storing Records

Described is a back-link method of storing records in the independent overflow area of Indexed Sequential Access Method (ISAM). Assuming N primary tracks of data, the new records which belong to the ith primary track and are to be added to the overflow area are denoted R(i1), R(i2)..., which is also the chronological order in which the overflow records are added. As records belonging to all the primary tracks are added in the same overflow area, in between R(ij) and R(ij+1) , records belonging to other primary tracks may be stored.

In the present ISAM method when a new record, say R(ij) , is to be added to the independent overflow area, it is stored in the first available space, but the linking is done in the following manner. The two records whose keys are just less than and greater than that of R(ij) are searched in the file. Suppose they are R'(ij) and R''(ij). The address of R(ij) is stored in the link field of R'(ij) and the address of R''(ij) is stored in the link field of R(ij).

In the back-link method of storage, the records belonging to a fixed track are linked in the reverse of the chronological order, i.e., the link field at the end of record R(ij+1) will contain the address of the record R(ij). Thus, the search for records in the overflow area is in the reverse order of the chronological order of storage.

The data field of the overflow entry of track-index will contain the address of the last chronological record be...