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This package defines the interface to a resource management
service (RMS) as used in the
de.danet.an.workflow.spis.ras sample
implementation. Note that the implementation of the workflow
core does not require a resource management service. However,
the sample resource assignment service (RAS) needs a resource
management service. We have based the sample RAS on this
interface to allow a deployer to use the sample RAS with any
resource management service by simply writing an adapter.
The service interface follows the standard conventions for a
service interface, i.e. it defines an abstract factory class
and a service interface.
Implementing this interface implies a particular problem. The
RMS must provide objects that implement
{@link de.danet.an.workflow.omgcore.WfResource WfResource}.
This interface has, as specified by OMG, methods workItems
isMemberOfWorkItems and release. While it
is obvious (from an OO point of view) that those methods are defined
as methods of WfResource the RMS
cannot really implement them. They can only be implemented by an
RAS, as it is its task to track assignments.
Thus the objects defined and returned by an RMS
can only implement the methods by delegating to the RAS.
There may, however, be several instances of RASs in an
environment that request resources from the RMS. How can the RMS
know, where to delegate to? One way to solve this problem would
be to have every RAS "register" itself with the RMS if it assigns
a resource from that RMS. This approach has a major drawback. In order
to be able to recover from an application restart, the RMS would have
to implement such a registry for RASs in persistent store. Depending
on the implementation of an RAS, this may be from difficult to
impossible.
A much more simple solution is to have a central runtime
registry of all available RASs and use the RASs registered there
to implement the above mentioned WfResource
methods(1).
This approach is even more charming as something very close to
such a registry exists anyway. While not designed to fulfill
this function in the first place, the
{@link de.danet.an.workflow.spis.ras.ResourceAssignmentServiceFactory ResourceAssignmentServiceFactory} actually implements
a kind of registry, as it must know about all RASs in the
system (else there is no way that the workflow core uses it for
resource assignment anyway).
The ResourceAssignmentServiceFactory therefore provides
the methods needed to implement workItems
isMemberOfWorkItems and release. As a
convenience this package provides a class
{@link de.danet.an.workflow.spis.rms.ResourceSupport ResourceSupport}
that uses the methods provided by the
ResourceAssignmentServiceFactory and can be directly
used by an RMS as base class for providing its implementation of
WfResource.
(1)Few things in life are free. There is
a small performance penalty to pay for this approach. As the RMS
doesn't keep track of the RASs that have requested a particular
resource, the central registry has to query all known RASs.
However, tracking RAS information (e.g. with identifiers usable
as hints for the central registry) in the RMS would impose an
overhead as well.
@since 1.0
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