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Declaration Offset Tables for Expert Data Bases

IP.com Disclosure Number: IPCOM000037237D
Original Publication Date: 1989-Dec-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Hendrickson, OK: AUTHOR

Abstract

Declaration offset tables (DOTs) and associated service routines indicate to a program the data format of a record and facilitate access to the data.

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Declaration Offset Tables for Expert Data Bases

Declaration offset tables (DOTs) and associated service routines indicate to a program the data format of a record and facilitate access to the data.

DOT accessing may be applied to any files that have static field definitions, a record-type field in each record, and unique identifiers for each type of record format. The same record format may be used in different files and the same file may use more than one record format.

When a program wishes to reference data in a record:

1. Ask the DOT service routines to identify the

record and return a symbol table containing a

description of each field in the record.

2. Give the DOT service routines a field name and ask

for DOT information about the field.

a. Offset from beginning of record to first

element

b. Length of element

c. Dimension of element

d. Spacing between elements if there is more

than one

3. Use the DOT information to access the data field.

The figure shows how the two service routines (identify and extract information) interact with the data and deliver DOT information about a particular field to the program.

For example, consider two different record formats. They could be either two different files with different record formats or one file with two types of records. Each record in the system must have a record-type field to identify it. The example will be to reference a bill of material number element named BMNUM.

Depending on which record type is being used, the bill of material number (BMNUM) is either in (using index origin 0) bytes 2-11 in record format 1 or bytes 4-13 in record format 2.

DCL 1 RECORD1 CHAR(80), /* Record format 1 */ 2 RCDTP CHAR(2), /* Record-type identifier */

2 BMNUM CHAR(10); /* Bill of material number */

DCL 1 RECORD2 CHAR(80), /* Record format 2 */ 2 RCDTP CHAR(2), /* Record-type identifier */

2 ELMTP CHAR(2), /* Other information */

2 BMNUM CHAR(10); /* Bill of material...