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Batch Dialog Execution

Dialog Execution

Batch dialog execution is similar to online dialog execution: a batch dialog executes premap and response processes and performs mapin and mapout operations. The major difference between batch and online dialogs is in the sequence and handling of the mapin (read) and mapout (write) operations.

The diagram below shows a typical batch dialog. The dialog reads from an input file and writes to an output file.

Premap Process

The premap process is executed at the beginning of the dialog, unless the dialog's entry point is its mapin operation. The process executes until it issues a control command, including a READ TRANSACTION or WRITE TRANSACTION command. In the example shown above, a READ TRANSACTION command is issued, which terminates the process and passes control to the mapin operation.

Mapin Operation

The mapin operation is performed in any of the following cases:

• At the beginning of the dialog if the dialog's entry point is its mapin operation
• After a READ TRANSACTION command has been issued by a premap or response process
• After a mapout operation that has been issued by a WRITE TRANSACTION command that does not include the CONTINUE or RETURN keyword
• After a CONTINUE command has been issued in a dialog without a premap process

The mapin operation performs the following functions:

1. Reads a record from the dialog's input file into the file's input buffer
2. Maps all correct fields into variable storage according to the dialog's input file map definition
3. Selects a response process based on batch control event or response field value

Note: If the application is defined using the application compiler, the runtime system first examines the response field of the record and passes control to another application function, if required. Application execution using the application compiler is described later in this chapter.

Response Process

The selected response process is executed after the mapin operation. The response process executes until it issues a control command, including a batch READ TRANSACTION or WRITE TRANSACTION command. In the example, the response process issues a WRITE TRANSACTION command, which causes a mapout operation.

Mapout Operation

A mapout operation is performed when a premap or response process issues a WRITE TRANSACTION command. The mapout operation either maps a record to the dialog's output file or writes the input record to the dialog's suspense file, as follows:

• A record is mapped to the output file if the dialog's current input file record (if any) contains no errors and if the WRITE TRANSACTION command does not include the keyword SUSPENSE. The mapout operation writes a record to the dialog's output file from variable storage according to the dialog's output file map definition.
• The input record is written to the suspense file if the dialog's current input file record contains errors or if the WRITE TRANSACTION command includes the keyword SUSPENSE. Applicable error messages are written to the log file. Note that an input field can be set in error either automatically on mapin or by map modification commands in process code.

Determining How Control Will Be Transferred

After the mapout operation, transfer of control is determined by the keyword specified in the WRITE TRANSACTION command that caused the mapout operation:

• CONTINUE executes the dialog's premap process.
• RETURN returns control to a higher level dialog or application function.

If no keyword is provided, the dialog's mapin operation is performed; this is the case below.

Note: Because the WRITE TRANSACTION command passes control to another part of the application, and because the command does not write to both the suspense file and the output file at the same time, it is difficult to write to both files if that is what you want. An alternative is to associate the output file map with a second dialog. The first dialog links to the second, which issues a WRITE TRANSACTION RETURN command. The command writes a record to the output file and returns to the first dialog. The first dialog then issues a WRITE TRANSACTION command that writes the input record to the suspense file.

Control Command Example

Control commands, including READ and WRITE TRANSACTION commands, the READ TRANSACTION and WRITE TRANSACTION commands, affect runtime flow of control. A few of these commands are illustrated below.

Accessing Multiple Input and Output Files

Control commands enable a batch application to consist of multiple dialogs. Through multiple dialogs, an application can access multiple input and output files, as shown below.

Application Execution

Application execution is described below:

1. DIALOG1's premap process issues a READ TRANSACTION command, which reads a record from the dialog's input file, then selects a response process.
2. DIALOG1's response process issues a LINK command, which passes control to DIALOG2.
3. DIALOG2's premap process issues a LINK command, which passes control to DIALOG3.
4. DIALOG3's mapin operation (the dialog's entry point) reads a record from the dialog's input file, then selects a response process.
5. DIALOG3's response process issues a RETURN command, which returns control to DIALOG2 at the command that immediately follows the LINK command.
6. DIALOG2's premap process issues a WRITE TRANSACTION RETURN command, which performs a mapout operation, writing a record to the dialog's output file, and returns control to DIALOG1 at the command that immediately follows the LINK command.
7. DIALOG1's response process issues a WRITE TRANSACTION command, which performs a mapout operation, writing a record to the dialog's output file, and performs a mapin operation, reading another record from the dialog's input file and selecting a response process.

For detailed information on the flow of control in a mapin operation, see Runtime Flow of Control.