BPEL4WS Stewart Green University of the West of England

17th November 2005SMRG: BPEL4WS2 Presentation Structure Purpose BPM Architecture Runtime Engine Theory: Petri Nets Theory: Pi Calculus Process Design Patterns Process Pattern Example BPEL4WS

17th November 2005SMRG: BPEL4WS3 Purpose Introduce BPEL4WS Introduce “Essential Business Process Modelling”, M. Havey, O’Reilly, 2005

17th November 2005SMRG: BPEL4WS4 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

17th November 2005SMRG: BPEL4WS5 BPM Architecture

17th November 2005SMRG: BPEL4WS6 BPM Architecture

17th November 2005SMRG: BPEL4WS7 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 Process Manager from Oracle may be trialled free htm

17th November 2005SMRG: BPEL4WS8 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)

17th November 2005SMRG: BPEL4WS9 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

17th November 2005SMRG: BPEL4WS10 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

17th November 2005SMRG: BPEL4WS11 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)

17th November 2005SMRG: BPEL4WS12 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

17th November 2005SMRG: BPEL4WS13 Process Patterns 20 patterns identified, see: Van der Aalst et al., Workflow Patterns, Distributed and Parallel Databases, 14(1): 5-51, 2003 Animations at Characteristics:  Spatial  Cluster of process activities arranged to solve a difficult problem  A wish list for a notational language

17th November 2005SMRG: BPEL4WS14 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

17th November 2005SMRG: BPEL4WS15 Process Patterns

17th November 2005SMRG: BPEL4WS16 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 , 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.

17th November 2005SMRG: BPEL4WS17 Process Patterns Write to variable C Run optical activity Write to variable C Write to variable C Run dental activity Write to variable C Write to variable C Run medical activity Write to variable C Mutual exclusion is used to ensure that patterns run serially: while one activity is running, the others are blocked

17th November 2005SMRG: BPEL4WS18 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 4 th 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

17th November 2005SMRG: BPEL4WS19 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

17th November 2005SMRG: BPEL4WS20 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

17th November 2005SMRG: BPEL4WS21 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.” (

17th November 2005SMRG: BPEL4WS22 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

17th November 2005SMRG: BPEL4WS23 BPEL4WS Business Process Execution Language for Web Services Written by IBM, MS, BEA & standardised by OASIS organisation ( 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)

17th November 2005SMRG: BPEL4WS24 BPEL4WS BPEL directly supports 13/20 P4 patterns directly and 1 indirectly

17th November 2005SMRG: BPEL4WS25 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.

17th November 2005SMRG: BPEL4WS26 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