A COBOL source element can reference data items either explicitly or implicitly in Procedure Division statements. An explicit reference occurs when the name of the referenced item is written in a Procedure Division statement or when the name of the referenced item is copied into the Procedure Division by the processing of a COPY statement
, a REPLACE statement
, an -INC statement, or ++INCLUDE statement
. An implicit reference occurs when the item is referenced by a Procedure Division statement without the name of the referenced item being written in the source statement.
An implicit reference also occurs during the execution of a PERFORM statement, when the index or data item referenced by the index-name or identifier specified in the VARYING, AFTER or UNTIL phrase is initialized, modified, or evaluated by the control mechanism associated with that PERFORM statement. Such an implicit reference occurs if and only if the data item contributes to the execution of the statement.