WS Orchestration
http://tmitwww.tm.tue.nl/staff/wvdaalst/Publications/p176.pdf
http://www-106.ibm.com/developerworks/webservices/library/ws-bpelcol2/
http://devresource.hp.com/drc/technical_white_papers/WSOrch/WSOrchestration.pdf
Eyal Oren
DERI
2004/04/07
Survey of WS orchestration
• definitions & requirements
• survey of standards
– BPEL4WS
– BPML
– WSCI
• survey of vendors
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Definitions
• orchestration
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executable process (that interacts with other web services)
control from the perspective of one business partner
for implementation
workflow
• choreography
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this is the private process, our
orchestration is subset of this
this is like our choreography
sequence of messages
public message exchanges
for collaboration
protocols
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Requirements
• a-synchronicity
we need to have this
– need message correlation: identifying returning calls
• exception management
we need to have this
– services (operations) throw & catch exceptions
• compensating transactions
we need to have this
– resource locking not feasible
• reusable composition:
– separation process logic – used web services
goal – capability separation
– don’t understand, looking for
hierarchy?
web service
– capability separation
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Standards overview
• BPEL4WS
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describes (control logic for) coordination of web services
Microsoft, IBM, BEA (XLANG & WSFL)
execution environment (BPWS4J)
not considered by W3C : not royalty-free
• BPML
– describes executable business processes
– Intalio, Sun, …, bpmi.org/members.esp
• WSCI
– describes messages between collaborating web services
– Sun, SAP, BEA, Intalio
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Standards relation
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BPEL4WS (1)
• (control logic for) coordination of web services
• abstract processes:
– choreography
– public message exchange
• executable processes:
– orchestration
– private workflow
• on top of WSDL
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BPEL4WS (2)
• primitive activity (input & input-output operations)
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invoke
receive
reply
wait
assign
throw
terminate
empty
(an operation on a web service)
(waiting for invocation)
(responding, in input/output operation)
(for … time)
(copy & compute data to variables)
(exception)
(stop service instance)
• structure activity (control flow)
– combines primitives using: sequence, branch, loop, pick, flow
– need more time to investigate possibilities
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BPEL4WS (3)
(WSDL defines messages, operations, porttypes)
• link
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describes conversation between two roles
(specifies porttype of service, to receive messages)
multiple messages can be exchanged during conversition
we need this too
partner: web service with role in linktype
(as Axel said on wsmo-d)
• business process: list of activities (with partners)
• actual web service grounding can be dynamic
– unclear yet (WS-Adressing)
– BPWS4J uses hard-wired at deploy
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BPML
• language for describing business processes
• simple activity
– action, assign, call, compensate, delay, fault, synch
• complex activity
– all, choice, foreach, sequence, switch, until, while
• transaction support (compensation, nesting)
• exception handling (throw, timeout)
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WSCI
• language for describing web services collaboration
• message correlation
• sequencing rules
– basic: call, delay, empty, fault, spawn, join
– complex: all, choice, foreach, sequence, switch, until, while
is this really only public
– but cannot specify input/output
message exchange then?
• exception handling
• transactions
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Comparison
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BPEL4WS – BPML+WSCI
intentions are the same
no comparison in the article, no thorough search
vd Aalst: pattern-based comparison:
– WSCI – BPML
• offer same functionality
• too much overlap to justify separation
• WSCI can be used to model
– BPEL4WS – BPML
• little more expressive
• no semantics
• too many overlapping constructs
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Useful for WSMO
• either: borrow requirements
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asynchronicity
exception management
compensation
message correlation
control flow construct (workflow patterns, vd Aalst)
• or: use a standard
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