The main role of a BPEL process is to orchestrate web services. Web services are presented in the BPEL processes as partner links. The orchestration is performed through the exchange of messages from one partner link to another. The variables hold the messages received from the partner links or from the message that is to be sent to the partner links. Of course, a variable can hold both types of messages at once. It is also possible that a variable can hold information that does not correspond to either the receiving or sending message.
A variable is described by the type of information it holds. The types of variable can be as follows:
A WSDL message type
An XML schema element
An XML schema simple type
The variables belonging to the outermost scope (defined inside the <scope> element) are called global variables. They can be accessed from anywhere within a BPEL process. Alternatively, we define a local variable that is accessible only within the enclosing scope. We define...