1、BPEL (Business Process Execution Language),presented by Cagdas E. Gerede01/24/06 Web Services and Security Seminar UC-Santa Barbara,Adaptation from Nirmal Mukhis slides,Business Process Execution Language,enables: Definition of Business Processes using Web Services Coordination of a set of Web servi
2、ce interactions Degree of interoperability at the process level (describe process and use it in different runtime infrastructures)where it comes from: Builds on XML and Web Services Convergence of two workflow languages (WSFL directed graphs; XLANG block-structured language),Orchestration,Versions,v
3、1.0 - BPEL4WS - August 2002 v1.1 March 2003 v2.0 Draft - WSBPEL OASIS (some issues discussed): how to use XPath whether there should be sub-processes in BPEL how abstract processes should be used,Simple Example,Composite Service - Orchestrated by BPEL,Traditional Flow Models,Activities represent uni
4、ts of processing.,Flow of data is explicitly modeled through data links.,Activities are mapped to application invocations or human actions,Control links define execution flow as a directed acyclic graph,Structure of a BPEL4WS Process,. . . . . (process body),BPEL Basic Activities,+,BPEL and WSDL Par
5、tners,Partner A,WSDL A,Partner B,Process,WSDL,Synchronous Communication,BPEL and WSDL. Partners,Partner B,Asynchronous Communication,Partner Definitions and Links,*,BPEL Data Model,Assignment activities move data around.,Activities input/ output is kept in global variables.,Globally scoped data vari
6、ables typed as WSDL messages,*,BPEL Composition of Web Services,Component A,As WSDL,Component B,Call Back,Bs WSDL,Process WSDL,More Basic Activities,BPEL Structured Activities,Nesting Structured Activities. Example,Flow,Seq,Seq,Seq,While,. ,“Flow Oriented” Authoring Style,Customer asks for a loan, g
7、iving name and amount info. Two services are involved: -A risk assessor which can approve the loan if the risk is low -A loan approver which checks the name and decides whether to approve the loan.The reply goes back to the customer.,“Structured” Authoring Style,BPEL Handlers and Scopes,Scope,Fault
8、Handler,CompensationHandler,A scope is a set of (basic or structured) activities.Each scope can have two types of handlers associated: Fault handlers. Many can be attached, for different fault types. Compensation handlers. A single compensation handler per scope.,How Handlers Work,A compensation han
9、dler is used to reverse the work performed by an already completed scope A compensation handler can only be invoked by the fault handler or compensation handler of its immediate enclosing scopeA fault handler defines alternate execution paths when a fault occurs within the scope.Typical scenario: Fa
10、ult is thrown (retuned by invoke or explicitly by process) Execution of scope is terminated Appropriate fault handler located (with usual propagation semantics) Main execution is compensated to “undo” business effects of unfinished work.,E,B,D,C,Fault,A,Scope and Fault Example,What is Correlation?,B
11、PEL can model many types of interactions: simple stateless interactions Stateful, long running, asynchronous interactions. Correlation sets (CSs) provide support for the latter: CSs represent the data that is used to maintain the state of the interaction (a “conversation”). At the process end of the
12、 interaction, CSs allow incoming messages to reach the right process instance. What is a correlation set? A set of business data fields that capture the state of the interaction (“correlating business data”). For example: a “purchase order number”, a “customer id”, etc. Each set is initialized once
13、Its values do not change in the course of the interaction.,Defining Correlation Sets,Using Correlation,BPEL Critique,No notion of independent activities - everything in a BPEL is a web service operation, not “an activity“, i.e. a unit of work No human interaction modeling Interacting activities inte
14、racting together two-by-two (multiple BPEL documents for a single process) BPEL can only represent multi-party collaboration that have a “center“ of control. (Ariba/CommerceOne - some B2B agent in the middle),- Questions -,Resources,BPEL4WS 1.0: http:/ BPWS4J Java Implementations: http:/ http:/ Two introductions to BPEL: http:/ http:/
