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9  The Runtime Environment                                      243






































                           Fig. 9.1 The Case Management Administration web form


                           9.3 Internal Architecture


                           Figure 9.2 presents a view of the internal architecture of the Engine, its major com-
                           ponents, and the relationships between them. At the core is the Engine Kernel,
                           which is responsible for the coordinated operation of the various components,
                           and manages interface communications with external services and applications.
                           Through the kernel, specifications are loaded, case instances are started and can-
                           celed, work items are managed, services are registered, and so on. The kernel also
                           takes care of the data-perspective, mapping values to and from tasks and their parent
                           nets, evaluating XQuery predicates, and storing those results.
                              The kernel communicates with custom services via the Engine’s four interfaces:
                           A (specification and session management); B (case and work item instance manage-
                           ment); E (process logging); and X (exception handling management) – see Chap. 7
                           for more details.
                              Each loaded specification is inserted into the Specification Store, which serves
                           as a repository for specification “templates” from which process instances may be
                           created. The store holds the specification until such time as it is manually removed
                           from the Engine. The store is persisted across server sessions (cf. Sect. 9.6).
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