Provide zero or more <catch> and one <catchall> element to catch faults and system errors.
To enable error handling, BPL defines an element called <scope>. A scope is a wrapper for a set of activities. This scope may contain one or more activities, one or more fault handlers, and zero or more compensation handlers. The <faulthandlers> element is intended to catch any errors that activities within the <scope> produce. The <catch> and <catchall> elements within <faulthandlers> may provide <compensate> statements that invoke <compensationhandler> elements to compensate for those errors.
When a <scope> provides no <faulthandlers> block, InterSystems IRIS automatically outputs the system error to the Event Log. When a <scope> does contain a <faulthandlers> block, the BPL business process must output <trace> messages to the Event Log for system error messages to appear there. System error messages appear on the Terminal console, in either case.
For details, see “Handling Errors in BPL” in Developing BPL Processes.
It is not possible to reverse the order of <compensationhandlers> and <faulthandlers>. If both blocks are provided, <compensationhandlers> must appear first and <faulthandlers> second.