Tecnologie per servizi web: WSDL, WSFL

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Models and Languages for Coordination and
Orchestration IMT- Institutions Markets
Technologies - Alti Studi Lucca
WS Technologies III BPEL4WS
Roberto Bruni Dipartimento di Informatica
Università di Pisa
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Contents

• Orchestration and Choreography
• WSFL
• Transactions and Compensations
• BPEL4WS

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WS Composition and Transactions Early Work

• eCo framework
• vague notion of orchestration
• created by CommerceNet to demonstrate the value
  of integrating e-commerce services
• focus on the document exchanges required for B2B
  integration
• WSCL (Web Services Conversation Language)
• somewhat analogous to web services choreography
• outlined a simple conversation language standard,
  
• focused on modeling the sequencing of interaction
  between web services

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WS Composition and Transactions Early Work

• WSFL
• IBM proposal
• flow model for orchestration, global model for
  choreography
• allowed for recursive (de)composition
• supported handling of exceptions
• had no direct support for transactions
• XLANG
• developed by Microsoft for the Microsoft BizTalk
  Server
• provided block-structured support for sequential,
  parallel, and conditional process control flow
• included a robust exception handling facility
• had support for long-running transactions through
  compensation

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WS Composition and Transactions WSCI

• Web Services Choreography Interface
• pronounced Whiskey
• proposed by Sun, SAP, BEA, and Intalio
• XML-based choreography language for WS
  collaboration
• abstract processes, not executable processes
• supports message correlation, sequencing rules,
  dynamic collaboration, exception handling and
  transactions
• only describes the observable behavior between WS
• each partner needs a single WSCI document
• a WSCI choreography includes a set of WSCI
  documents

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WS Composition and Transactions BPML

• Business Process Management Language
• developed by Business Process Management
  Initiative (BPMI.org), chartered by Intalio,
  Sterling Commerce, Sun, CSC, and others
• initially designed to support executable business
  processes (over a BPMS), but the first draft also
  incorporated the WSCI protocol
• basic activities for sending, receiving, and
  invoking services
• structured activities that handle conditional
  choices, sequential and parallel activities,
  joins, looping, and scheduling of tasks at
  specific times
• other features include persistence, roles,
  instance correlation, and recursive decomposition

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WS Composition and Transactions BPEL4WS

• Business Process Execution Language for Web
  Services
• promoted by IBM, Microsoft, and BEA
• supersedes XLANG and WSFL (but is far more
  complex)
• XML-based grammar, leveraging WSDL for describing
  the control logic
• abstract processes (called business protocols)
• executable processes (over an orchestration
  engine)
• includes support for both basic and structured
  activities
• mechanism for catching and handling faults (like
  Java)
• compensatory activities via compensation handler

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WS Composition and Transactions
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WS Composition and Transactions

• BTP (Business Transactions Protocol)
• emerging proposal by OASIS (Organization for
  Advance Structured Information Systems),
  involving HP, Oracle, BEA
• aimed to B2B transactions in loosely coupled
  domains (not specifically for WS)
• WS-Coordination by W3C
• describes how services can make use of
  pre-defined coordination contexts to subscribe to
  a particular role in a collaborative activity
• WS-Transaction by W3C
• provides a framework for incorporating
  transactional semantics into coordinated
  activities.

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Business Process Execution Language for Web
Services

• BPEL4WS v1.1 (5 May 2003)
• released along with two others specifications
• WS-Coordination and WS-Transaction
• block-structured language (like XLANG),
• allowing recursive blocks but restricting
  definitions and declarations to the top level
• activities as the basic components
• structured activities for sequential control
  include sequence, switch, and while
• also nondeterministic choice based on external
  events (pick)
• concurrency and synchronization between
  activities is provided by flow (like WSFL)

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BPEL4WS Terminology

• Partners (service providers)
• a subset of the partner links of the process
• Partner links
• the services with which a business process
  interacts
• each partner link is characterized by a
  partnerLinkType
• Partner link type
• characterizes the conversational relationship
  between two services
• by defining the "roles" played by each of the
  services in the conversation
• and specifying the portType provided by each
  service to receive messages within the context of
  the conversation

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BPEL4WS Terminology

• Variables
• provide the means for holding messages that
  constitute the state of a business process
• variables can also hold data that are needed for
  holding state related to the process and never
  exchanged with partners
• the type of each variable may be a WSDL message
  type, an XML Schema simple type or an XML Schema
  element

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BPEL4WS Activities

• ltreceivegt
• blocking wait for a matching message to arrive
• ltreplygt
• to send a message in reply to a message that was
  received through a ltreceivegt
• the combination of a ltreceivegt and a ltreplygt
  forms a request-response operation on the WSDL
  portType
• ltinvokegt
• to invoke a one-way or request-response operation
  on a portType offered by a partner

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BPEL4WS Activities

• ltassigngt
• to update the values of variables with new data
• copying data from one variable to another is a
  common task within a business process
• a single ltassigngt construct can contain any
  number of elementary assignments
• this activity can also be used to copy endpoint
  references to and from partner links

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BPEL4WS Activities

• ltthrowgt
• to generate a fault from inside the business
  process
• ltwaitgt
• to wait for a given time period or until a
  certain time has passed
• ltemptygt
• nil activity (useful for synchronization of
  concurrent activities)

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BPEL4WS Activities

• ltsequencegt
• to define a collection of activities to be
  performed sequentially in lexical order
• ltswitchgt
• to select exactly one branch from a set of
  choices
• ltwhilegt
• to indicate that an activity is to be repeated
  until a certain success criteria has been met

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BPEL4WS Activities

• ltpickgt
• to block and wait for a suitable message to
  arrive
• or for a time-out alarm to go off
• when one of these triggers occurs, the associated
  activity is performed and the pick completes
• ltflowgt
• to specify one or more activities to be performed
  concurrently
• links can be used within concurrent activities to
  define arbitrary control structures, but with
  great care
• ex. a link MUST NOT cross the boundary of a while
  activity, a serializable scope, an event handler
  or a compensation handler

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BPEL4WS Activities

• ltscopegt
• to define a nested activity with its own
  associated variables, fault handlers, and
  compensation handler
• ltcompensategt
• to invoke compensation on an inner scope that has
  already completed normally
• can be invoked only from within a fault handler
  or another compensation handler

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BPEL4WS Other Features

• Message correlation (like WSCI)
• Transition and join conditions
• dead path elimination
• Fault handlers
• Compensation handlers
• Event Handlers
• Serializable scopes
• ...

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Its Not a Stack, Its a Web of Dependencies
BPEL 1.1
WS-ReliableMessaging
WS-Coordination
WS-Transaction
WS-Addressing
Xpath 1.0
WS-Security
WS-Trust
WSDL 1.1
WS-Policy
WS-SecurityAddendum
SOAP 1.2
WS-PolicyAssertions
WS-SecurityPolicy
WS-Routing
WS-PolicyAttachments
XML Schema 1.0
A Partial View (? Gartner)
WS-SecureConversation
XML Signature
XML Encryption
X.509
XML 1.0
XML Infoset
XML Namespaces
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Vendor Landscape

• BEA WebLogic Workshop
• while BEA contributed to both the BPEL4WS and
  WSCI initiatives, it does not provide native
  support for either standard
• Collaxa Orchestration Server
• supports BPEL4WS, WS-Coordination, WS-Transaction
• IBM BPWS4J
• Java runtime platform for BPEL editor
• Sun WSCI Editor
• supports WSCI (in pat), not BPEL