Information Technology Reference
In-Depth Information
The following forms are proposed to express the user/domain
preferences discussed earlier.
Type I
.
condition
WS
2
;
Type II
.
switch(condition){case C
1
:
?
WS
1
:
WS
1
;
case C
2
:
WS
2
;...;
}
; and
Type III
.
WS
1
case C
n
:
WS
n
;
WS
2
WS
n
.
The above-mentioned expressions are similar to some general
expressions in software engineering and programming languages.
Especially, the first two expressions are the conditional ones commonly
used in C, C
, and Java. The first one evaluates the expression
“
condition
” first. If it is TRUE, then executes service
WS
1
, and
otherwise executes service
WS
2
. The second one also evaluates the
truth value of expression “
condition
” first, and then executes the
corresponding service accordingly. The third expression means that
WS
1
has higher priority than
WS
2
, and
WS
2
has higher priority than
WS
3
, and so on. In other words,
WS
2
will be executed only if
WS
1
fails,
and
WS
3
will be executed only if
WS
1
and
WS
2
both fail, and so forth.
þþ
6.3 WEB SERVICE COMPOSITIONWITH
BRANCH STRUCTURES
6.3.1 Basic Ideas and Concepts
In PHISP, we combine several key technologies and methodologies
for service composition, so as to provide customizable and personal-
ized medical and health care services for individuals. However,
achieving automatic Web service composition (WSC) to support
more control constructs for better performance is a challenging issue.
In the domain of health care, workflows like Figure 6.2 can be
generated by domain experts using domain knowledge. However,
when the system is general public-oriented, the needs of users are
often uncertain, diverse, and personalized. Consequently, defining all
the possible workflow templates in advance becomes very difficult if
not impossible. Thus, generating composite services with sophisti-
cated control constructs automatically is very meaningful and impor-
tant, even in this specific domain. This section focuses on the service
