Information Technology Reference
In-Depth Information
identical and the only difference is the execution order of services
Physi_Info_Ac
quir,
Envir_Info_Acquir
,
Subj_Feel_Acquir
,and
E_M_R
.
Moreover, any one of the solutions has its execution time equal to the sum
of execution time of all the four services, while with parallel processing,
the total execution time restswith the slowest time among the four services
as shown in Figure 6.2. It should be noted that when a single-processor
computer is used to execute the services, the results will be identical.
Generally speaking, identifying all the possible parallel cases of
component services is usually very difficult in service composition.
However, when we consider this problem inside an enterprise, the
situation becomes more manageable. In our platform, we present a few
simple rules and adopt some techniques to support parallel structures
when composing services.
We introduce the concept of
layer
first. In the process of service
composition, starting from the initial state, after every step of reasoning
we can obtain a set of newly executable services. We call these services
at the same layer. Those states that are associated with services at the
same layer are also called states at the same layer, and elements of each
state set are in the form of propositions, and thus we call this type of
layers proposition layers. Then we define a binary mutual exclusion
(BME) relation between services. Two services at a same layer in a
process of service composition are mutually exclusive if no valid
solutions could possibly contain both of them. Identifying such relation-
ships can help construct parallel structures.
We notice and record BME relationships by two simple rules.
Specifically, there are two ways in which services
WS
1
and
WS
2
at a
given layer are marked to be mutually exclusive.
BME 1
. If either of the services disables a precondition of the other.
. If their preconditions are marked to be mutually exclusive
in their corresponding higher proposition layer.
Two propositions
p
and
q
in a proposition layer are marked to be
mutually exclusive if any of the services that generates proposition
p
is
mutually exclusive with any that generates
q
. Preconditions of a service
mentioned in the two rules specify the conditions that must be true in
order for an agent to execute the service.
With these two rules, we can identify parallel component services to
a certain extent. We give an identification rule as follows.
P-Rule
BME 2
. The services that are not marked to be mutually exclusive
of each other in the same service layer can be executed in parallel.
