Grid Services Orchestration with OMII-BPEL - Grid Computing: Infrastructure, Service, and Applications - page 200

menus, and so on to reduce the burden of operational details and simplify
user interactions with the editor. Users can better concentrate on overall
process modeling and related coni gurations. We can easily i nd some
examples to illustrate our discussions.
When a user creates a new process, BPEL Designer allows the use of
templates to start with rather than from scratch. There are both synchro-
nous and asynchronous templates to choose from, all of which will generate
the skeleton process and a WSDL descriptor that the user does not have
to bother editing immediately. After a few steps of setup following the
creation wizard, the user can start composing right away. Apparently, this
is of great convenience to avoid repeated editing of basic BPEL and WSDL
documents for every process to be created.
In order to model a service interaction, we have mentioned that a corre-
sponding partner link dei nition must be declared to associate the partner
service with the process model. As difi cult as this may be for BPEL begin-
ners to comprehend, the actual editing of a partner link declaration that
involves both the process document and WSDL descriptor(s) could be frus-
trating. BPEL Designer has been able to simplify this by bringing a series of
wizard pages that walk through all required steps. A partner link will be
unmistakably declared in the end without the user noticing any changes in
i les at all. The wizard can be started from the declaration panel explicitly
or on the l y when dei ning relevant activities (e.g., invoke , receive , and reply ).
During the declaration, an important step is to import the WSDL descrip-
tion of the partner service so that the information derived can be used to
dei ne service interactions in the process. BPEL Designer supports the
import of WSDL i les from a i le system, Eclipse project space, or remote
locations with given URLs. Once a WSDL description is imported, the ser-
vice interface as well as any associated schema dei nitions will be stored
and made available throughout the process project. BPEL Designer will ren-
der them into an expandable tree controller. Users can simply pick up the
corresponding nodes on the tree to associate with the current partner link
declaration without having to go through the actual WSDL description. A
similar use of tree controllers can be found in a number of occasions in
BPEL Designer.
For example, in order to dei ne a service invocation, one must provide the
information of partner link, port type, operation, and input/output vari-
ables altogether for an invoke activity. In the properties view ( Figure 8.2 ) ,
candidate values can be selected from the drop-down lists respectively. Or
preferably, simply picking the intended operation node on the tree will have
all the i elds i lled up automatically without further operation from the
user. Input/output variables will be created on the user's behalf if they
do not exist already by silently resolving the operation and the associated
message dei nitions of the imported WSDL. The variable panel will be updated
with the new declarations accordingly. This is more than a useful feature as
users tend to put off variable declarations until they are actually needed.