Chapter 13: Process Specifications

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• Chapter 13Process Specifications

Service-Oriented Computing Semantics, Processes,
Agents Munindar P. Singh and Michael N. Huhns,
Wiley, 2005
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Highlights of this Chapter

• Processes
• Describing Dynamics with UML
• Workflows
• Business Process Languages
• BPEL4WS (WS-BPEL)
• ebXML
• RosettaNet
• PSL Process Specification Language

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Processes and Workflows
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A Process Is Abstractions

• Orchestration A partial order of actions
  (activity graph, script) under the control of a
  central conductor akin to a workflow Global
  view central
• Workflow narrower concept than process
  emphasizes control and data flows from a central
  perspective usually tool-specific and focused on
  human tasks
• Choreography An exchange of messages among
  participants akin to a conversation as described
  by WSCL, WS-CDL, ebBP Global view distributed
• Collaboration A joint set of activities among
  business partners Local views distributed

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Telecommunications Order Processing
Older workflow tools support specialized (ad hoc)
notations
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Describing Dynamics with UML

• UML Activity Diagrams are practically identical
  to BPMN (Business Process Modeling Notation) and
  WS-BPEL (Business Process Execution Language)
• Sequence a transition from one activity to the
  next
• Branch a decision point among alternative flows
  of control
• Merge where two or more alternative flows of
  control rejoin
• Fork a splitting of a flow of control into two
  or more concurrent and independent flows of
  control
• Join a synchronization of two or more
  concurrently executing flows of control into one
  flow

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UML Activity Diagram
Implementation of a vendors purchase process
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Flow Interoperability Patterns

• Among others
• Chained
• Nested
• Synchronized

• What guarantees would you obtain from each?
• How would you accommodate exceptions in each?

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WS-BPEL Metamodel
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Process as a Composite Web Service
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Stock Quote Service in WS-BPEL

• ltprocess name"simple" targetNamespace"urnstockQ
  uoter" xmlnstns"urnstockQuoter"
  xmlnssqp"http//tempuri.org/services/stockquote"
  xmlnsBPEL/gt
• ltcontainersgt
• ltcontainer name"request" messageType"tnsreq
  uest"/gt
• ltcontainer name"response" messageType"tnsre
  sponse"/gt
• ltcontainer name"invocationRequest"
  messageType"sqpGetQInput"/gt
• ltcontainer name"invocationResponse"
  messageType"sqpGetQOutput"/gt
• lt/containersgt
• ltpartnersgt
• ltpartner name"caller" serviceLinkType"tnsSt
  ockQuoteSLT"/gt
• ltpartner name"provider" serviceLinkType"tns
  StockQuoteSLT"/gt
• lt/partnersgt
• ltsequence name"sequence"gt
• ltreceive name"receive" partner"caller"
  portType"tnsStockQuotePT"
• operation"wantQuote"
  container"request" createInstance"yes"/gt
• ltassigngt ltcopygt
• ltfrom container"request"
  part"symbol"/gt
• ltto container"invocationRequest"
  part"symbol"/gt
• lt/copygt lt/assigngt

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Electronic Business Extensible Markup Language
(ebXML)

• Established jointly by
• UN-CEFACT (United Nations Centre for Trade
  Facilitation and Electronic Business)
• OASIS (Organization for the Advancement of
  Structured Information Standards)
• Provides specification languages for business
  processes, business messages to facilitate
  trading agreements
• Motivations
• Global standard for companies of all sizes
• Automate finding business partners

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ebXML Vocabulary

• Unified Modeling Methodology (UMM)
• Specialized UML for Business Processes
• Collaboration Protocol Profile (CPP)
• Describes a business with respect to its roles in
  specified processes, the messages it exchanges,
  and the transport mechanism (e.g., HTTPS)
• Collaborative Partner Agreement (CPA)
• Intuitively, like an intersection of two CPPs
• Technical agreement between two or more partners
• May be legally binding

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Design of an ebXML System
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Discover Partner Information and Negotiate
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Implementing ebXML

• ebXML is a set of specifications of
  collaborations and repositories for discovering
  business partners
• Build and deploy its custom ebXML-compliant
  application to implement necessary roles in
  different collaborations
• Use COTS ebXML compliant applications and
  components (from ERP vendors)
• Business Service Interface (BSI) a wrapper that
  enables a given party to participate properly in
  an ebXML exchange

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Business Service Interface

• Interfaces with the legacy system to have it play
  a role in a specific protocol (e.g., vendor in
  3A4)
• Is aware of its own Collaborative Protocol
  Profile
• Handles transactions based on all current
  agreements (CPAs)

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RosettaNet PIP for Creating a Purchase Order The
Content for ebXML

• PIP Partner Interface Process an interaction
  protocol
• ebXML BPSS language for specifying PIPs

• Two-party protocols
• Request-response only
• No specification of the meanings of the messages
  exchanged

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Exercise Exception in a Process

• Recording student registration
• Assume that each database management system
  supports two-phase commit for transactions
• Task 2 checks that the student has completed the
  necessary prerequisites for all the courses for
  which the student is registering
• Consider a scenario where Tasks 3, 4, 5
  succeed, but Task 2 fails
• As the system administrator, what operations
  would you have to perform in order to restore
  consistency to your system?
• How would you modify the process to prevent
  problems such as this from occurring?

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Chapter 13 Summary

• In virtually all serious applications of SOC,
  services are composed into processes
• Current approaches for process modeling are based
  on workflow abstractions
• WS-BPEL enables specification of processes
• ebXML also considers the life cycle of processes
• RosettaNet is an application of ebXML
• Flows interact in various ways
• Exceptions in flows can be handled via (extended)
  transactions or through application-specific
  means (where interesting patterns can arise)