Exercise 7. Give two benefits offered by the Worklet Service’s approach to excep- tion handling over more manual approaches. Exercise 8. Can you think of any runtime exceptions that may occur that cannot be captured by the approach discussed in this chapter?
172 M. Adams and N. Russell Chapter Notes Exception Patterns The application of a pattern-based approach to defining exception handling strate- gies and their use for assessing the exception handling capabilities of PAIS was first described in . This paper also proposed the notion of a graphical exception han- dling language for defining exception handling strategies, a notion that ultimately led to the development of YAWLeX, the language on which the exlet strategies in YAWL were realized. A comprehensive assessment of the exception handling capabilities of a number of leading workflow and case handling systems, business process modeling notations, and business process execution languages is contained in . Worklets/Exlets The use of the worklets paradigm for exception handling was first discussed in , and a full description of the conceptual framework of worklets, exlets, and dynamic exception handling was further detailed in . A full exploration of the worklet approach, including a complete formalization and exemplary studies, can be found in . Other Approaches The need for reliable, resilient, and consistent workflow operation has long been rec- ognized . Early work in the area [90,268] was essentially a logical continuation of database transaction theory and focussed on developing extensions to the classic ACID transaction model that would be applicable in application areas requiring the use of long duration and more flexible transactions. As the field of workflow tech- nology matured, the applicability of exceptions to this problem was also recognized [226, 244]. In , Eder and Liebhart presented the first significant discussion on workflow recovery that incorporated exceptions, and gave the now classic catego- rization of workflow exceptions into four groups: basic failures, application failures, expected exceptions, and unexpected exceptions. Subsequent research efforts into workflow exceptions have mainly concentrated on the last two of these classes, and on this basis, the field has essentially bifurcated into two research areas. Inves- tigations into expected exceptions have focussed previous work on transactional workflow into mechanisms for introducing exception handling frameworks into workflow systems. Research into unexpected exceptions has established the areas of adaptive workflow and workflow evolution . Although it is not possible to comprehensively survey these research areas in the confines of this chapter, it is worthwhile identifying some of the major contributions in these areas that have influenced subsequent research efforts and have a bearing on
5 Exception Handling 173 this research initiative. Significant attempts to include advanced transactional con-
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