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element of any business-oriented SOA. However, this is not the case when you
look at the hierarchy graphics; Process is a child node in the Composition.
Generally, a top-level Composition consists of Processes and presents the Master
Composition, not the other way around. On the other hand, in the OWL schema,
the Process consists of Compositions. At the same time,
ServiceComposi-
tion
is a subset of the Composition and has no direct relation to the Service it-
self. We agree that a Process, Composition, and
ServiceComposition
can
(or cannot) be presented as a Service. However, in this case, a Service should be
taken out of the hierarchy and placed separately, close to the Event.
• The
ServiceContract
and
ServiceInterface
classes are separate ele-
ments of hierarchy, and this could create some confusion. Generally, Open Group
describes a contract in terms of SLA, which includes parties involved in service
activities and their legal obligations.
ServiceInterface
has a more technical
nature and presents an RPC-like access point for message-based invocations (not
a totally correct term as we have DOC-type services, not RPC-style ones;
however, we hope that you get the idea). Therefore, we can expect some attributes
as
Operation
or
Task
(again, in WSDL terms). Indeed,
Task
is the property
of the
ServiceInterface
class. At the same time, you will find this property
in the
ServiceContract
class. An example of the
Task
property is provided
by OWL: "
WashWindows
is an instance of
Task
, performed by the service pro-
vider (John)."
• In addition to
Task
, both contract and interface have something called Effect. Ef-
fect represents the outcome of service interaction and holds value for the custom-
er. Here, we have another inconsistency. If our interface is message-oriented and a
message is a transportable form of an object, then the logical outcome of the ser-
vice operation is a new (changed) state of the object. An object's noticeable
change is an Event—"The weather has changed. Expect heavy rain in ... hours."
So, what is the Event according to the Open Group ontology?
• An Event is described as an occurrence on an Element to which an Element may
choose to respond. From this, we understand that an Element is, in fact, an Ob-
ject. An Element is at the top of practically any hierarchy. You will find an Ele-
ment at the top of the Open Group Ontology as well; only an Effect will be high-
er. An Event is detached and located at the bottom of the hierarchy. The logic un-
derlying this decision is not entirely clear.
• The authors tried to avoid using the term "Object" and proposed a superclass for
Element,
Thing
. What's wrong with the old "Object" is completely unclear as
well.
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