A process can display information to operators using any of the following features: DISPLAY statements, instruction blocks, and fetch specifications.
DISPLAY statements are the most commonly used of these methods. The DISPLAY statement is implemented in ALGOL, COBOL, and WFL. This feature is also available as the Display procedure in Pascal. The following is a WFL example of this statement:
DISPLAY “INCORPORATING NEW DATA - MAY TAKE AWHILE”;
The output from a DISPLAY statement is referred to as a DISPLAY message. The DISPLAY message appears as one of the entries in the response to the MSG (Display Messages) system command. If the process is initiated from a CANDE or MARC session, the DISPLAY message is automatically displayed at the session. The programmer can use the DISPLAYONLYTOMCS task attribute to limit the display of the message to the originating session. If this task attribute is TRUE, then the DISPLAY message does not appear at the ODT.
You can use instruction blocks to store information that an operator can display at any time. By contrast, DISPLAY messages are only temporarily visible to the operator, because the MSG command displays only the most recent system messages. Instruction blocks are created using the INSTRUCTION statement, which is available only in WFL. The following is an example of this statement:
INSTRUCTION 3 TESTTAPE IS IN TAPE RACK 3.;
An operator can use the IB (Instruction Block) system command to display instruction blocks for a WFL job. For example, a command of the form 7645 IB displays the most recent instruction block for the WFL job with mix number 7645. A command of the form 7645 IB 3 displays instruction block 3 for that WFL job.
The disadvantage of instruction blocks is that nothing prompts the operator to use the IB command. The operator has to know in advance that instruction blocks exist for a particular WFL job. If you want to be sure that an operator sees a message, you can use the FETCH task attribute. This task attribute can be used only in WFL jobs, and only in the job attribute list at the start of the job. You can assign any arbitrary string of text to this attribute. The following is an example of a FETCH assignment:
FETCH = “THIS JOB NEEDS THREE TAPE DRIVES”;
If the operating system option NOFETCH is not set, then when a WFL job containing a FETCH assignment reaches the head of a job queue, the system suspends the job rather than initiating it. The job appears in the W (Waiting Mix Entries) system command display with an RSVP message of REQUIRES FETCH. The operator can use the PF (Print Fetch) system command to display the FETCH specification, and the OK (Reactivate) system command to cause the job to be initiated.
If NOFETCH is set, then the system does not suspend jobs with FETCH specifications. However, the PF system command can still be used to display FETCH specifications.
If you enter a PF command for a process that has no FETCH specification, the system displays the message “NO FETCH STATEMENT.”
