BPEL4WS

1
BPEL4WS

• Stewart Green
• University of the West of England

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Presentation Structure

• Purpose
• BPM Architecture
• Runtime Engine
• Theory Petri Nets
• Theory Pi Calculus
• Process Design Patterns
• Process Pattern Example
• BPEL4WS

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Purpose

• Introduce BPEL4WS
• Introduce Essential Business Process Modelling,
  M. Havey, OReilly, 2005

4
BPM Architecture

• Havey reviewed the 17 candidate BPM standards for
  an application architecture with the ability to
• Design, run, and monitor and administer business
  processes that incorporate human and system
  interactions

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BPM Architecture
6
BPM Architecture
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Runtime Engine

• BPM engine
• Loads programs (process definitions)
• Runs instances of them (process instances)
• BPEL4WS preferred execution language
• Most popular
• Supports most canonical process patterns (see
  later)
• ActiveBPEL is an open source implementation
• http//www.activebpel.org
• Process Manager from Oracle may be trialled free
• http//www.oracle.com/technology/products/ias/bpel
  /index.htm

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Theory Petri Nets

• Petri nets
• Good at describing control flow semantics
• Van de Aalst et al have developed theory around
  process pattern flow semantics and the Petri net
• Havey asserts that judged on the basis of
  control flow, the strongest languages are those
  that are based on Petri nets, including BPEL
  since they support more common control flow
  patterns (see later)

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Theory Petri Nets

• Petri nets help describe and can be used to
  implement the semantics of process control
  flow, including basic branch and join rules, as
  well as more complicated synchronisation
  scenarios notably dead path elimination

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Theory Pi Calculus

• Pi calculus is an algebraic system for building
  process that communicate with each other on
  channels
• Each process has a control flow that supports
  sequential, conditional or concurrent control
  flow
• When one process sends information to another, it
  includes the name of the channel to be used for
  the other process to respond. This name is
  variable it may change in response to changing
  conditions. Channel change is called mobility
• The leading choreography language, WS-CDL, bases
  its constructions and channel passing on the pi
  calculus

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Theory Pi Calculus

• Pi calculus has 3 key features for BPM
• Control flow support for
• Sequential process behaviours
• Conditional process behaviours
• Parallel process behaviours
• Recursive process behaviours
• Message-based communication
• Clean syntax for inbound outbound messaging
• Mobility
• Contemporary processes require the ability to
  pass around and change addresses dynamically
  (mobility)

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Process Design Patterns

• Vander Aalst et al. (the process 4 or P4) have
  documented process patterns to help process
  designers
• Six categories
• Basic
• Advanced split and join
• Structured
• State-based
• Cancellation
• Multiple instances

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Process Patterns

• 20 patterns identified, see
• Van der Aalst et al., Workflow Patterns,
  Distributed and Parallel Databases, 14(1) 5-51,
  2003
• Animations at www.workflowpatterns.com
• Characteristics
• Spatial
• Cluster of process activities arranged to solve a
  difficult problem
• A wish list for a notational language

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Process Patterns Example

• Interleaved parallel routing
• Intent several activities are to be performed in
  sequence, but order of execution is arbitrary and
  not known at design time, e.g. an applicant to
  the army must take 3 tests medical, dental and
  optical but I doesnt matter in what order

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Process Patterns
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Process Patterns

• Most BPM vendors and standards lack support for
  interleaved parallel routing
• BPEL offers a solution (see van der Aalst et al.,
  Pattern Based Analysis of BPEL4WS, QUT Technical
  Report FIT-TR-2002-04, Queensland University of
  Technology, 2002
• Mutual exclusion is used to ensure that paths run
  serially and while one activity is running the
  others are blocked.

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Process Patterns

• ltflowgt
• ltscope nameoptical variableAccessSerializable
  yesgt
• ltsequencegt
• Write to variable C
• Run optical activity
• Write to variable C
• lt/sequencegt
• ltscopegt
• ltscope namedental variableAccessSerializable
  yesgt
• ltsequencegt
• Write to variable C
• Run dental activity
• Write to variable C
• lt/sequencegt
• ltscopegt
• ltscope namemedical variableAccessSerializable
  yesgt
• ltsequencegt
• Write to variable C
• Run medical activity

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Process Patterns

• The P4 rated 15 vendors offerings (see van der
  Aalst et al., Workflow Patterns On the
  Expressive Power of (Petri net based) workflow
  languages, in K. Jensen (ed.), Proceedings of the
  4th Workshop on the Practical Use of Coloured
  Petri Nets and CPM tools (CPN 2002) vol 560 of
  DAMI, p 1 20, University of Aarhus, 2002
• Even indirectly, most failed to support 10 of the
  20 patterns

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Process Patterns

• Communication patterns
• Receive request
• A process triggered by an inbound service
  request in BPEL pattern is implemented with the
  receive activity
• Call Partner Service
• A process sends a message to a partners service
  in BPLE invoke
• Human workflow patterns

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BPEL4WS

• Business Process Execution Language for Web
  Services (BPEL4WS or BPEL) is an XML Schema-based
  abstraction that enables the composition of
  multiple synchronous and asynchronous Web
  services into an end-to-end business flow.
  (Principles of BPEL, Orchestration, and the ESB
  from www.capeclear.com)

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BPEL4WS

• A BPEL script is an XML document that conforms
  to the BPEL schema. The BPEL script is
  interpreted at runtime by a BPEL processor
  engine that identifies keywords or activities
  and executes them as defined in the BPEL script.
  (www.capeclear.com)

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BPEL4WS

• BPEL process programs can
• Communicate by exchanging messages with other web
  services using receive, reply, and invoke
  activities
• Control execution flow using while, switch,
  sequence, pick, flow, and wait activities
• Handle faults that can occur during processing
  using catch and catchall activities
• Model event-driven programming using onMessage
  and onAlarm event handlers
• Roll back transactions using compensation
  handlers

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BPEL4WS

• Business Process Execution Language for Web
  Services
• Written by IBM, MS, BEA standardised by OASIS
  organisation (www.oasis-open.org)
• Antecedents
• XML Language (XLANG) from MS (claimed to be
  influenced by pi calculus)
• Web Services Flow Language (WSFL) from IBM
  (claimed to be influenced by Petri net)

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BPEL4WS

• BPEL directly supports 13/20 P4 patterns directly
  and 1 indirectly

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BPEL4WS

• The source code for a BPEL XML-based process
  definition is
• A set of Web Service Definition Language (WSDL)
  files specifying the web services
• A BPEL XML file for the process logic
• The process definition references the WSDL
  partner link types and variables based on WSDL
  defined message types.

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BPEL4WS

• Web Services Definition Language (WSDL) is the
  standard format specifying services implemented
  by and called by the process in terms of
• Port types
• Partner link types
• Message types
• Properties