BPEL4WS

Stewart GreenUniversity of the West of England

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Presentation Structure

PurposeBPM ArchitectureRuntime EngineTheory: Petri NetsTheory: Pi CalculusProcess Design PatternsProcess Pattern ExampleBPEL4WS

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Purpose

Introduce BPEL4WSIntroduce “Essential Business Process Modelling”, M. Havey, O’Reilly, 2005

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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

Runtime Engine

External Processes

Administration and Monitoring Console

Choreography toolkit: Code generator; compliance

validator

Internal applications

Human worklist application

Process database

Generates or

validates

Management language Standard worklist

interface

Deploy

Read & write

Exporter

BusinessAnalyst

Technical Analyst

System Administrator

Process Participant

Web services

Graphical Editor

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BPM Architecture

Runtime EngineBPEL4WS

. Most expressive. BPMN mapping

. Most industry supportEnterprise Java Beans

External ProcessesWeb service based

communications with processes of other

companies covered by choreographies or B2B

collaborations

Administration and Monitoring Console

JSP Web application

Choreography toolkit: Code generator; compliance

validatorWS-CDL

Internal applications

EJB, JMS, JCA, JDBC, web

services via serve lets

Human worklist application

JSP web application

Process database

JDBC access

Generates or

validates

Management language

(Java management extensions)

BPQL? BPDM?

Standard worklist interface

Deploy

Read & write

BusinessAnalyst

Technical Analyst

System Administrator

Process Participant

Web services

Example: ITPearls Process Modeller BPMN tool with BPEL exporter

Web services via servelets

EJB

Offline utility

Graphical EditorBPMN

. Most expressive. BPEL mappingOffline windows

app.

Exporter (BPMN-2-BPEL)

Offline utility

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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 channelsEach process has a control flow that supports sequential, conditional or concurrent control flowWhen 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 mobilityThe 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 doesn’t matter in what order

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Process Patterns

Interleave split Dental

Medical

Optical

Interleave join

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Process Patterns

Most BPM vendors and standards lack support for interleaved parallel routingBPEL 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, 2002Mutual 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 <flow> <scope name=”optical” variableAccessSerializable=”yes”> <sequence> Write to variable C Run optical activity Write to variable C </sequence> <scope> <scope name=”dental” variableAccessSerializable=”yes”> <sequence> Write to variable C Run dental activity Write to variable C </sequence> <scope> <scope name=”medical” variableAccessSerializable=”yes”> <sequence> Write to variable C Run medical activity Write to variable C </sequence> <scope>

Mutual exclusion is used to ensure that patterns run serially: while one activity is running, the others are blocked

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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, 2002Even 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 partner’s 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 ServicesWritten 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