Business Process Execution Language

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Jewel Lloyd
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1 Business Process Execution Language

2 Business Process Execution Language Define business processes as coordinated sets of Web service interactions Define both abstract and executable processes Enable the creation of compositions of Web services Where it comes from: Strong roots in traditional flow models Concepts from structured programming languages On top of WSDL and core XML specifications Merges WSFL and XLANG concepts The OASIS WS BPEL Technical Committee is advancing the BPEL4WS Specification Web Services: BPEL 2

3 BPEL & WSDL Shipping Services porttype Invoice Services porttype Receive Purchase Order Production Scheduling porttype Initiate Price Calculation Decide On Shipper Initiate Production Scheduling Purchase Order porttype Complete Price Calculation Arrange Logistics Complete Production Scheduling Invoice Processing Web Services: BPEL 3

4 BPEL & WSDL Shipping Services porttype Invoice Services porttype Receive Purchase Order Production Scheduling porttype Initiate Price Calculation Decide On Shipper Initiate Production Scheduling operation Purchase Order porttype Complete Price Calculation Arrange Logistics Complete Production Scheduling message Invoice Processing Web Services: BPEL 4

5 BPEL & WSDL Shipping Services porttype Invoice Services porttype Receive Purchase Order Production Scheduling porttype Initiate Price Calculation Decide On Shipper Initiate Production Scheduling operation Purchase Order porttype Complete Price Calculation Arrange Logistics Complete Production Scheduling <porttype name= schedulingpt <operation name= requestproductionscheduling > <input message= pos:pomessage /> </operation> Invoice Processing <operation name= sendshippingschedule > <input message= pos:schedulemessage /> </operation> </porttype> message Web Services: BPEL 5

6 Structure of a BPEL Process <process...> <partners>... </partners> <containers>... </containers> <correlationsets>... </correlationsets> <faulthandlers>... </faulthandlers> <compensationhandlers>... </compensationhandlers> (activities)* Web services the process interacts with Data used by the process Used to support asynchronous interactions Alternate execution path to deal with faulty conditions Code to execute when undoing an action What the process actually does </process> Web Services: BPEL 6

7 BPEL and WSDL Partners Partner B Partner A WSDL WSDL A Process Web Services: BPEL 7

8 BPEL and WSDL Partners Partner B Partner A WSDL A Service Link Type Web Services: BPEL 8

9 Partner Links Partner links are used to represent interactions between a service and each of the parties with which it interacts Partner links define the messages and port types used in the interactions in both directions, along with role names Web Services: BPEL 9

10 Partner Definitions and Links A partner is accessed over a WS channel, defined by a service link type <partner name=... servicelinktype=... partnerrole=... myrole=... /> A SLT defines two roles and the porttypes that each role needs to support <servicelinktype name=... > <role name=..."> <porttype name=... />* </role> <role name=... > <porttype name=... />* </role> </servicelinktype> Web Services: BPEL 10

11 Partner Links Purchasing partner link Invoicing partner link Scheduling partner link <partnerlink name="scheduling" partnerlinktype="lns:schedulinglt" partnerrole="schedulingservice"/> <plnk:partnerlinktype name="schedulinglt"> <plnk:role name="schedulingservice"> Shipping partner link <plnk:porttype name="pos:schedulingpt"/> </plnk:role> </plnk:partnerlinktype> The porttype used in the partner link Web Services: BPEL 11

12 Traditional Flow Models Control links define execution flow as a directed acyclic graph Activities represent units of processing Flow of data is explicitly modeled through data links Activities are mapped to application invocations or human actions Web Services: BPEL 12

13 BPEL Data Model Globally scoped data variables typed as WSDL messages Activities input / output is kept in global variables Assignment activities move data around <container name=... message=... />* Web Services: BPEL 13

.. [createinstance=... ] /> Sends a reply message in partner invocation <reply partner=... porttype=... operation=... container=.

14 BPEL Basic Activities Invokes an operation on a partner <invoke partner=... porttype=... operation=... inputcontainer=... outputcontainer=... /> Receives invocation from a partner <receive partner=... porttype=... operation=... container=... [createinstance=... ] /> Sends a reply message in partner invocation <reply partner=... porttype=... operation=... container=... /> Data assignment between containers <assign> <copy> <from container=... /> <to container=... /> </copy>+ </assign> Web Services: BPEL 14

15 BPEL Composition of Web Services Process WSDL Component B Component A B s WSDL A s WSDL Service Link Type Web Services: BPEL 15

16 More Basic Activities Detects processing error and switches into fault processing mode <throw faultname=... faultcontainer=... /> Pull the plug on this instance <terminate/> Execution stops for a specified amount of time <wait for=...? until=...? /> Do nothing; a convenience element <empty> Web Services: BPEL 16

17 BPEL Structured Activities <sequence> execute activities sequentially <flow> execute activities in parallel <while> iterate execution of activities until condition is violated <pick> several event activities (receive message, timer event) scheduled for execution in parallel; first one is selected and corresponding code executed <link...> defines a control dependency between a source activity and a target Web Services: BPEL 17

18 Nesting Structured Activities: Example <sequence> <receive.../> <flow> <sequence> <invoke... /> <while... > <assign>... </assign> </while> </sequence> <sequence> <receive... /> <invoke... /> </sequence> </flow> <reply... /> </sequence> Seq Flow Seq Seq While Web Services: BPEL 18

19 Asynchronous Interactions in BPEL BPEL can model many types of interactions: Simple stateless interactions Stateful, long running, asynchronous interactions For the latter case, how to ensure that two (or more) messages are referring to the same session? Web Services: BPEL 19

20 Message Correlation Associating two or more messages with each other in an asynchronous environment Done by associating contents in a given message with its correlating message For example, in a purchase order/invoice scenario, the invoice may contain the corresponding purchase order number Purchase Order: <PurchaseOrder> <PurchaseOrderNumber> <PurchaseOrderDate>... </PurchaseOrder> Invoice: <Invoice> <InvoiceNumber> <InvoiceDate> <PurchaseOrderNumber>... </Invoice> common in both messages Web Services: BPEL 20

21 Correlation Sets What is a correlation set? A set of business data fields that capture the state of the interaction ( correlating business data ), e.g., a purchase order number, a customer id, etc. Each set is initialized once Its values do not change in the course of the interaction CSs : the data used to maintain the state of the interaction (a conversation ) At the process end of the interaction, CSs allow incoming messages to reach the right process instance Web Services: BPEL 21

22 Defining Correlation Sets A CS is a named set of properties. Properties are defined as WSDL extensibility elements <correlationset name=... properties=... /> A property has a simple XSD type and a global name <bpws:property name=... type=... /> Web Services: BPEL 22

23 Properties A property is mapped to a field in a WSDL message type <bpws:propertyalias propertyname=... messagetype=... part=... query=... /> The property can thus be found in the messages actually exchanged Typically a property will be mapped to several different message types and carried on many interactions, across operations and porttypes Web Services: BPEL 23

24 Using Correlation An input or output operation identifies which correlation sets apply to the messages received or sent <receive partner=... operation=... porttype=... container=... > <correlations> <correlation set= PurchaseOrder initiation= yes /> </correlations> </receive> That CS will be used to assure that the message is related to the appropriate stateful interaction A CS is initialized once, in an interaction where the set appears with the initiation attribute set to yes. Its value may never be changed afterward Web Services: BPEL 24

25 Example: Defining Correlation Sets A customer ID and order number represent a unique purchase order <correlationset name= PurchaseOrder properties= cor:customerid cor:ordernumber /> <correlationset name= Invoice properties= cor:vendorid cor:invoicenumber /> A vendor ID and invoice number represent a unique invoice Web Services: BPEL 25

26 Example: Using Correlation Sets Declares correlation between purchase order and invoice <invoke partnerlink= Buyer porttype= SP:BuyerPT operation= AsyncPurchaseResponse inputvariable= POResponse > <correlations> <correlation set= PurchaseOrder initiate= no pattern= out > <correlation set= Invoice initiate= yes pattern= out > </correlations> </invoke> Web Services: BPEL 26

27 BPEL Handlers and Scopes 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 handler A single compensation handler per scope scope Fault Handler Compensation Handler Web Services: BPEL 27

28 Scope and Fault Example A Fault B C E D Web Services: BPEL 28

29 How Handlers Work A fault handler defines alternate execution paths when a fault occurs within the scope Typical scenario: 1. Fault is thrown (retuned by invoke or explicitly by process) 2. Execution of scope is terminated 3. Appropriate fault handler located (with usual propagation semantics) 4. Main execution is compensated to undo business effects of unfinished work A compensation handler 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 scope Web Services: BPEL 29

30 Partial Work Unavoidable Business processes are often of long duration, which means that a business process may need to be cancelled after many transactions have been committed during its progress Consider a situation in which a user cancels a purchase order: Revert back to original state Submit Purchase Order Process Purchase Order Check Inventory Order From Supplier User Cancels! In this situation, it is not possible to lock system resources (ex: database records) for extended periods of time Therefore, the partial work must be undone as best as possible Web Services: BPEL 30

31 Compensation Handlers Invoked to perform compensation activities a wrapper for compensation activities: Specifies a compensating operation on a given porttype for a given partner link: <compensationhandler> <invoke partnerlink= Seller porttype= SP:Purchasing operation= CancelPurchase inputvariable= getresponse outputvariable= getconfirmation > <correlations> <correlation set= PurchaseOrder pattern= out /> </correlations> </invoke> </compensationhandler> The CancelPurchase operation invokes a cancellation The response to the purchase request is used as input Web Services: BPEL 31

32 Dynamic Service Selection and Invocation The relevant information about a partner service can be set up as part of business process deployment This is a more static approach However, it is also possible to select and assign partner services dynamically BPEL uses endpoint references defined in the WS- Addressing specification for this capability <wsa:endpointreference xmlns:wsa=... > <wsa:address> <wsa:porttype>purchaseorderporttype</wsa:porttype> </wsa:endpointreference> PortType and Address assocation Web Services: BPEL 32

Composing Web Services using BPEL4WS

Composing Web Services using BPEL4WS Francisco Curbera, Frank Leymann, Rania Khalaf IBM Business Process Execution Language BPEL4WS enables: Defining business processes as coordinated sets of Web service