Why does my service have no partners?

Why does my servicehave no partner?
Diagnosing uncontrollability
Niels Lohmann
WS-FM 2008 ▪ Milan ▪ 5 September 2008
http://service-technology.org/wsfm2008
UNIVERSITÄT ROSTOCK

Controllability
"soundness for services"
answer to "Does my service have partners?" or "Can anyone use my service?"
existence of partner proves controllability
implemented in tool Fiona (see next talk)
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Uncontrollable services
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decision not communicated (non-local choice): resubmission necessary?

Uncontrollable services (2)
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infinite message queue necessary: not controllable

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WS-BPEL
asynchronous message transfer yields non-local choice:which branch was taken?

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YAWL
decision communicated, but control flow may deadlock

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Open Petri Net
control flow may run into livelock

Uncontrollability
can have many different reasons
is independent of specification language
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Patterns for Uncontrollability
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controllable net containing the pattern
pattern for non-local choice
controllable net containing the pattern

Uncontrollability
is a non-local criterion
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Relationship to Soundness
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unsound, uncontrollable
sound, uncontrollable
sound, controllable
relaxed sound, uncontrollable
unsound, controllable

Uncontrollability
has no relationship to soundness
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Witness for controllability
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✗
remaining graph iswitness for controllability

Witness for uncontrollability
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✗
✗
✗
✗
✗
no graph left to witness
uncontrollability

Uncontrollability
has no relationship to soundness
current algorithm provides no witness
next step (very briefly):
provide diagnosis information
answer "Why does my service have no partners?"
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Diagnosing Uncontrollability
goal: find reasonable partof the graph
idea: partition graph into two parts:
good: no error occurred (yet)
bad: error already occurred or unavoidable
diagnosis: analyze moves from good to bad part
realization: blacklists
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Blacklists
preprocessing of the open net
deadlocks and livelocks(communication-independent issues)
during graph generation
covered final marking(can be related to a non-local choice)
exceeded message bound
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Diagnosis Algorithm
consider states that can be left with sending events
if successors are blacklisted, print the reason
otherwise consider non-blacklisted successors
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non-local choice between b and c may yield to cover final marking!

Wrap up
uncontrollability…
is a very undesired property of a service
can have a lot of reasons
cannot be avoided using anti-patterns
can now be diagnosed!
next steps:
implementation
provide assistance towards controllability
extend diagnosis to cope with choreographies
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Thank you!
Any questions?