Only One 01 Rule

For writable tables, unless all of the columns in a table are bound to items that are located in the same 01-level item, each record type on which a table is defined must explicitly contain exactly one item at the 01 level.

This 01-level item determines the length of inserted records which use that record type unless the file definition includes a record size Working-Storage Section item.

This example shows multiple 01-level items (PRODUCT-RECORD, BACK-ORDER-RECORD and DISCONTINUED-RECORD) included in the same record type (BACK-ORDER-RECORD). A table that contained this record type could not be written to unless all of the columns are derived from items belonging to a single 01 level item. That is, all must belong to PRODUCT-RECORD, all must belong to BACK-ORDER-RECORD, or all must belong to DISCONTINUED-RECORD. This is the only way that the correct 01 level can be selected for the COBOL WRITE or REWRITE. A simple rule to follow for writable tables is to define a record type for each level 01.

This rule does not imply that the 01 Level that is part of the record type must be part of the table. Adding a 01 Level to a table with any other items will probably violate the Same Item Rule.