Databases Reference
In-Depth Information
Partner links
All interaction between a process and other parties (or partners) is via web services,
as defined by their corresponding WSDL files. Even though each service is fully
described by its WSDL, it fails to define the relationship between the process and the
partner, that is, who the consumer of a service is and who the provider is. At first
glance, the relationship may seem implicit. However, this is not always the case, so
BPEL uses partner links to explicitly define this relationship.
Partner links are defined using the
<partnerLinkType>
, which is an extension to
WSDL (defined by the BPEL standard). Whenever you refer to a web service whose
WSDL doesn't contain a
<partnerLinkType>
, JDeveloper will automatically ask
you whether you want it to create one for you. Assuming your answer is yes, it will
create this as a separate WSDL document, which then imports the original WSDL.
Messaging activities
BPEL defines three messaging activities
<receive>
,
<reply>
, and
<invoke>
; how
you use these depends on whether the message interaction is either synchronous or
asynchronous and whether the BPEL process is either a consumer or provider of
the service.
Synchronous messaging
With synchronous messaging the caller will block until it has received a reply
(or times out), that is, the BPEL process will wait for a reply before moving on
to the next activity.
As we can see in the following,
Process A
uses the
<invoke>
activity to call a
synchronous web service (
Process B
in this case), once it has sent the initial
request, it blocks and waits for a corresponding reply from
Process B
.
Process B
uses the
<receive>
activity to receive the request. Once it has processed
the request, it uses the
<reply>
activity to send a response back to
Process A
.
