Information Technology Reference
In-Depth Information
4
Compensable Programs
The ability to declare compensation logic alongside forware-working logic is
the underpinning of the application-controlled error-handling framework of WS-
BPEL. This section will provide a model for compensable programs which consist
of forward activity (for application task), backward activity (for compensation)
and exception handling component.
A compensable program will be identified as a healthy design with the al-
phabet containing the following variables to record the status of the holder of
compensation program and the values of program variables:
1. x and x : to stand for the initial value and the final value of variable x
respectively.
2. Cseq : to keep the compensation programs installed so far.
3. Cpens : to record the named compensation programs. It is a mapping from
the scope names to their corresponding compensation programs.
4.1
Primitive Commands
The chaotic program
is defined as usual
true
true
true
beh (
)= df
The execution of skip terminates successfully, leaving both the contents of the
holder of compensation programs and the values of program variables and target
lables unchanged.
true
Identity
true
true
beh ( skip )= df
where the binary relation Identity is defined by
( v = v )
( Cpens = Cpens )
( Cseq = Cseq )
Identity = df
The program fail stops the execution indicating the failure of the forward
activity.
true
true
true
beh ( fail )= df
Identity
There is a class of programs which never end the execution with a meaningful
outcome. The assignment x := 1 / 0 belongs to this category. We use the notation
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