Service Composition - Guide to Cloud Computing for Business and Technology Managers - page 224

reply : The reply activity sends a message in reply.
invoke : The invoke activity calls a Web Service operation of a partner
service. This can either be a one-way or a request-response call.
One way means that the called service will not send a response,
whereas request-response blocks the process until a response is
received.
assign : The assign activity updates the values of variables or partner
links with new data.
validate : The validate activity checks the correctness of XML data stored
in variables.
wait : The wait activity pauses the process, either for a given time period
or until a certain point in time has passed.
empty : The empty activity is a no-op instruction for a business process.
Another element of the WS-BPEL language is a variable. BPEL supports both
global (i.e., process level) and local (i.e., scope level) variables. BPEL variables
may be typed using an XML schema (XSD) type or element or a WSDL mes-
sage. For initializing or assigning variables, BPEL provides the assign activ-
ity. Each assign consists of one or more copy statements. In each copy, the
from element specifies the assignment source for data elements or partner
links, and the to element specifies the assignment target.
Additionally, there are basic activities that deal with fault situations:
throw : The throw activity generates a fault from inside the business
process.
rethrow : The rethrow activity propagates a fault from inside a fault han-
dler to an enclosing scope, where the process itself is the outermost
scope.
compensate : The compensate activity invokes compensation on all com-
pleted child scopes in default order.
compensateScope : The compensateScope activity invokes compensation
on one particular (completed) child scope.
exit : The exit activity immediately terminates the execution of a busi-
ness process instance.
Furthermore, WS-BPEL offers structured activities. Structured activities can
have other activities as children; that is, they represent container activities.
WS-BPEL consists of the following structured activities:
low : The activities contained in a flow are executed in parallel, partially
ordered through control links. A flow activity represents a directed
graph. Note that cyclic control links are not allowed.