A standalone subprocess is defined, as shown in the following example, in a file with the extension .sbpel (subprocess BPEL extension).

<!-- A subprocess is defined in a SBPEL file, containing a bpelx:subProcess
 ! document
 ! The bpelx:subProcess is similar to a standard bpel:process, with
 ! differences asnoted below.
-->

<bpelx:subProcess name="NCName" targetNamespace="anyURI"
   xmlns="http://docs.oasis-open.org/wsbpel/2.0/process/executable"
   xmlns:bpelx="http://schemas.oracle.com/bpel/extension" ...>

   <!-- Partner links and variables serve as sub-process arguments -->
   <partnerLinks>?
      <partnerLink name="NCName" partnerLinkType="QName" myRole="NCName"?
         partnerRole="NCName"?
         bpelx:argumentRequired=["yes"|"no"]? />
   <partnerLinks>
   <variables>?
      <variable name="BPELVariableName"  messageType="QName"? type="QName"?
         element="QName"?
         bpelx:argumentRequired=["yes"|"no"]?>
         from-spec?
      </variable>
   </variables>

  <!-- Standard process definition here, except no <receive> or <pick> with -->
  <!--  createInstance="yes" -->
  /activity/
</bpelx:subProcess>

The <subProcess> element is an extension of the WS-BPEL 2.0 language. The <subProcess> element is the root element for a subprocess definition. The namespace for this element is as follows:

http://schemas.oracle.com/bpel/extension

The <subProcess> activity must be embedded in an <extensionActivity>, as specified in section 10.9 of the Web Services Business Process Execution Language Specification Version 2.0.

A subprocess is of type tProcess, as defined in the following WS-BPEL target namespace:

http://docs.oasis-open.org/wsbpel/2.0/process/executable

It differs from tProcess in the following ways:

• Variables and partner links immediately under the <subProcess> element can serve as arguments for the subprocess. Required arguments are marked by setting the attribute argumentRequired to yes (the default value is no). The subprocess's required arguments are the minimum set of arguments the caller must pass to it.

• A variable defined with an inline from-spec initializer serves as an optional argument with a default value. If the caller passes this argument, the caller-supplied value for the argument overrides the default value.

• Validation reports an error if a variable is referenced prior to setting the value if it is not a required argument.

• The first activity in the subprocess cannot be a receive or pick activity with createInstance set to yes. This is because no instance of a given subprocess type is created; the subprocess is logically part of an existing process instance.

The subprocess /@name attribute defines the name of the subprocess that is unique within the composite in which it is deployed.

The subprocess is self-contained. That is, all the variable and partner link references in the process snippet resolve to local definitions or arguments. This contrasts with the <inlineSubProcess> element, which allows unresolved references to variables and partner links that are in-scope at the call activity.

In a typical scenario, more than one variable is exchanged between the parent and a subprocess. If they are large documents, copying them is expensive. Because of this, passing by reference is an option.

A subprocess can converse with partners synchronously (InOut) or asynchronously (InOnly). The partner link for these interactions can be passed as an argument from a parent process or configured within the subprocess. For asynchronous requests, the conversation ID for WS-Addressing/normalized messages is set with the parent process instance ID. This enables routing of callback messages to the correct process instance.

Subprocesses in a SOA composite application are enumerated in the composite.xml file. The component element definition associates a subprocess's name with the sbpel file in which it is defined. During deployment, the subprocess components are delegated to the BPEL process service engine. The BPEL process service engine validates the process definition and builds a map with the subprocess target name as the key and the subprocess definition as the value. At most, only one instance of a subprocess exists in the service engine independent of consumer count. For optimizing memory, it may lazily load the process or unload the process if it is not actively used.

For information about creating a standalone subprocess, see How to Create a Standalone BPEL Subprocess.