Used to communicate a failure of the overall workflow to interested parties.
Implement and use with the WorkflowInstanceFacade to listen for data production events from the underlying workflow instance
The interaction point with a workflow instance.
A WorkflowRunCancellation is passed to listeners when a workflow run is cancelled.
Although T2 has no 'real' concept of a workflow instance, using identifiers on data instead, it is useful to treat it as if it does. The facade classes are the external 'invoke only' interface to the enactment system, providing wrappers around the actual single instance model. This also hides the shared state tree, exposing only the sub-tree rooted at the base ID internal to the facade layer. The state tree acts both as monitoring and steering infrastructure, the facade therefore prevents a process accessing the state of another workflow either maliciously or inadvertently.
The construction of these facade objects is not defined here, a factory method in the implementation package is the most likely candidate but there are other options, for example a peer to peer cloud may expose services to create new facades and allow access as might a web service based interface. The interfaces here are intended to be as easy to access remotely as possible.
For the same reasons there are no methods in the workflow facade concerning security or the management of data access - it is assumed that the constructor of the facade layer has embedded such concerns within it. There is therefore a clear split between initiation of the workflow session and manipulation of it with this package only addressing the latter of the two.
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