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162                                              M. Adams and N. Russell


                                                                                     YAWL
                                                                                     Editor
                                                                         Worklet
                                      X
                                                          Worklet        Specs
                              YAWL                        Service
                                      A
                              engine                      Selection
                                                                         Rules
                                      B                   Exception                   Rules
                                                                                      Editor
                                                                         Logs







                               YAWL
                              worklist
                                                           user
                           Fig. 5.7 External architecture of the worklet service



                           for uploading to the engine, and generated process and audit logs. The YAWL Edi-
                           tor is used to create new worklet specifications, and may be invoked from the Rules
                           Editor, which is used to create new or augment existing rule sets, making use of cer-
                           tain selection logs to do so, and to graphically define exlets, and may communicate
                           with the Worklet Service via a JSP/Servlet interface to override worklet/exlet selec-
                           tions following rule set additions. The service also provides servlet pages that allow
                           users to directly communicate with the service to raise external exceptions and to
                           create and carry out administration tasks.
                              Any YAWL specification may have an associated rule set. The rule set for each
                           specification is stored as XML data in a disk file that has the same name as the spec-
                           ification’s identifier, but with an “.xrs” extension (signifying an “XML Rule Set”).
                           Each YAWL specification has a single rule-set file for all selection and exception
                           rules defined for it. All rule set files are stored in the rules folder of the Worklet
                           Repository.
                              To enable the Worklet Service to serve the YAWL workflow enactment engine, a
                           number of events and methods must be provided by an interface between them,
                           some originating from the service side and others from the engine side. Some
                           require a response, while others do not require any acknowledgment (such as event
                           notifications that do not necessarily require action).
                              The first four methods described for the selection interface in Chap. 4 are also
                           used by the exception handling procedure. In addition, the exception interface
                           requires a further set of events and methods. The enactment engine must notify
                           the service for the following events:
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