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74 N. Russell and A. ter Hofstede
A work item comes into existence in the created state. This indicates that the
preconditions required for its enablement have been satisfied and it is capable of
being executed. At this point, however, the work item has not been allocated to a
resource for execution and there are a number of possible paths through these states
that individual work items may take. Each edge within this diagram is prefixed with
either an S or an R, indicating that the transition is initiated by the system (i.e., the
software environment in which instances of the process execute) or resource (i.e.,
an actual user), respectively. Transitions between all states once the work item has
been created up until when it is started can be initiated either by the system or by a
resource depending on how the specific work distribution directives for the associ-
ated have been configured. Once a work item is started, any further state transitions
are triggered by the resource responsible for the work item up until the time that it
is completed or failed. Each state has a specific meaning in terms of how the work
item is handled:
Created means that the work item has come into existence but no resources are
yet aware of it.
Offered to a single resource indicates that the opportunity to undertake the work
item rests with a single resource and that the resource has not yet committed to
undertaking it.
Offered to multiple resources indicates that several resources have been offered
the opportunity to undertake the work item but none have elected to do so as yet.
Once one of them does commit to executing the work item, the offers received
by other resources are withdrawn.
Allocated indicates that a specific resource has elected (or been requested) to
undertake the work item but has not yet started working on it.
Started indicates that the responsible resource has commenced executing the
work item.
Suspended indicates that the responsible resource has elected to cease execution
of the work item for a period, but does intend to continue working on it at a later
time.
Failed indicates that the work item cannot be completed and that the resource
will not work on it any further.
Completed identifies that a work item that has been successfully executed to
completion.

2.6.3 Interaction Strategies

The potential range of interaction strategies that can be specified for tasks in YAWL
are listed in Table 2.7. They are based on the specification at three main interaction
points – offer, allocation, and start – of the identity of the party that will be respon-
sible for determining when the interaction will occur. This can be a resource (i.e.,
an actual user) or the system. Depending on the combination of parties specified for
each interaction, a range of possible distributions are possible as described. From