2.1 Exception Handling Patterns
In the field of Workflow Management System (WFMS), researchers analyzed the different workflow exceptions, and divided them into four classes: basic failures, application failures, expected and unexpected exceptions (Eder & Liebhart, 1995) and expected and unexpected exceptions are main topics which are addressed in WFMS. For expected exceptions, early research focuses on extensions to the classic ACID transaction model (Eder & Liebhart, 1995) (Worah & Sheth, 1997). For unexpected exceptions, adaptive workflow, workflow evolution and other technologies are proposed proposed (Rinderle, Reichert, & Dadam, 2004). In paper Workflow Exception Patterns (Russell, van der Aalst, & ter Hofstede, 2006), the authors investigate the range of issues that may raise exceptions during process execution, and the paper proposed five expected types of exception: work item failure, deadline expiry, resource unavailability, external trigger and constraint violation. There are three groups of specific handling strategy (Russell, van der Aalst, & ter Hofstede, 2006): exception handling at work item level, exception handling at case level and recovery action. For exception handling at work item level, there are 15 handling strategies. For exception handling at case level and recovery action, there are 3 handling strategies for each of them. The exception patterns take the form of tuples comprising the three elements (Russell, van der Aalst, & ter Hofstede, 2006): exception handling at work item level, exception handling at case level and recovery action. For the purpose of practice, there are 36 exception handling patterns.
Besides exception handling patterns, Researchers have summarized various kinds of Workflow-related patterns which contain Workflow Patterns (van der Aalst, ter Hofstede, Kiepuszewski, & Barros, 2003), Workflow Data Patterns (Russell, ter Hofstede, Edmond, & van der Aalst, 2004a), Workflow Resource Patterns (Russell, ter Hofstede, Edmond, & van der Aalst, Workflow Resource Patterns, 2004b), and so on.