Introduction and Advanced Concepts of BPEL

Introduction and Advanced

Concepts of BPEL

Denis Weerasiri & Waruna Ranasinghe

Overview

• What is BPEL

• WSO2 Business Process Server

• Introduction to BPEL

• HelloWorld Sample

• Advanced Concepts of BPEL

• Fault Handling

• Compensation Handling

• Correlation and Async processes

• Extending WSO2 BPS

What is BPEL

• An OASIS standard executable language for

business processes

• More or less a service composition language

• Enables composition of (business) services into

business processes

• XML based language

Why Automate Business Processes

• Increase Efficiency

• No need to worry about the coordination of the

process

• Improve Responsiveness

• Business processes are agile

• Improve the process

• Adapt to the change of business needs

Business Process wrt BPEL

Business Process is a collection of coordinated

service invocations and related activities that

produce a result, either within a single organization

or across several organizations

Why BPEL

• Agility

• No need to worry about low level programming stuff.

• Native support for long running processes

• Compose larger business processes out of smaller

processes and services

• Handle message-related and time-related events

• Industry standard language for expressing

business processes

• Leverage common skill set

Why BPEL

• Portability

• Managed execution

• Monitor the progress of the process

• Start, stop, suspend, resume process instance

WSO2 Business Process Server

• Executes business processes written using WS-

BPEL standard

• Powered by Apache ODE

• Provide a web-based management console

• Deploy processes

• Manage and view business processes

• Manage and view process instances

• Configure QoS and many more…

Why WSO2 BPS

• WSO2 Carbon Studio – BPEL Editor

• Drag and drop process modeler

• Native BPEL support

• XPath editor

• Deploy processes to WSO2 BPS

• Support both BPEL4WS 1.1 and WS-BPEL 2.0

• Graphical Management Console to:

• Deploy and manage business processes

• Manage and monitor process instances

• Configure QoS perameters

Why WSO2 BPS

• Process dehydration

• Process versioning

• Follow open standards – avoid vender lock-in

• Support XQuery and Xpath, XSLT

• Support BPEL Extensions

• Features from WSO2 Carbon

Want to implement Business Processes?

• What you should already know

• XML

• XML Namespaces

• XML Schema

• WSDL

• XPath

• XSLT and XQuery (optional)

Introduction to BPEL

• BPEL Concepts

• Activities

• Basic Activities

• Structured Activities

• HelloWorld sample process

BPEL Concepts

Partner Links

• Defines the “Contact channels” between

external world (clients/partner services)

Partner Links

• Associates interfaces (WSDL ports) with roles,

using PartnerLinkTypes

PartnerLinkType

• Characterizes the conversational relationship

between two services

• Define the roles played by each of the services in

the conversation

<plnk:partnerLinkType name="BuyerSellerLink">

<plnk:role name="Buyer" portType="buy:BuyerPortType" />

<plnk:role name="Seller" portType="sell:SellerPortType" />

</plnk:partnerLinkType>

PartnerLynkType

Seller Buyer

Process Partner Service

Invoke Seller

Send response to Buyer’s Callback

Seller Buyer

Process Partner Service

Invoke Seller

Async Sync

Partner Link

• Associates with a partnerLinkType

<partnerLinks>

<partnerLink name=“BuyerSellerPL”

partnerLinkType=“BuyerSellerLink”

myRole=“Buyer”

partnerRole=“Seller”/>

</partnerLinks>

• Defines which role should be played by the

process itself and the partner service

Variables and Data Manipulation

• Variables

• Statically typed(via WSDL Messages, XSD elements

and XSD types)

• Assigning values to variables

• When message is received from a partner

• Manipulate variables inside <assign> activity

• Require knowledge about XPath, XQuery, XSLT

Activities in BPEL

• Basic Activities

• Structured Activities

Basic Activities

• Receive

• Reply

• Invoke

• Assign

• Wait

• Empty

• Compensate

• Catch

• Throw

• Rethrow

• Exit

Receive

• Act as the entry point to the business process

• Receives messages from an external partner

• Associated with

• PartnerLink with myRole

• WSDL operation

• Variable for the incoming message

• createInstance="yes" to create a new process

instance, otherwise the incoming message will be

consumed by the (already running) process

instance

Reply

• Sends the response back to the client

• Always relates to a “receive” activity

• Associated with

• Same PartnerLink for the “receive”

• Same operation for the “receive”

• Variable for the output message

Invoke

• Used to consume partner services

• Associated with

• PartnerLink with at least a “partnerRole”

• WSDL operation of the partner service

• Input variable

• Output variable, if the operation is request-

response

Assign

• Used to manipulate variables

Initializing Variables

• Variables contain a piece of XML

• Manipulated using Xpath

• XPath is evaluated on XML

• The variable should be initialized before copying

values to the internal elements.

What we want

myProfile =

<profile>

<name>Waruna</name>

</profile>

What we got

• String variable “name” – “Waruna”

• Variable “myProfile” – “”

• “myProfile” variable should be initialized before

copying the “name” variable into the “name”

element of “myProfile” variable

• $myProfile/profile/name

Initialization

• myProfile =

<profile>

<name></name>

</profile>

• Then copy the “name” into “name” element of

the “myProfile” variable.

• $myProfile/profile/name

Activities in BPEL

• Basic Activities

• Structured Activities

Structured Activities

• Sequence

• Flow

• While

• RepeatUntil

• ForEach

• If

• Pick

• Scope

Sequence

• Contained activities will be executed in an

ordered manner

Flow

• Execute contained activities in parallel

Looping

• While, RepeatUntil, ForEach

• Provides repeated execution of the contained

activity

If

• Provides conditional behavior

Pick

• Waits for the occurrence of exactly one event

from a set of events.

• OnMessage

• OnAlarm

Scope

• Group activities into logical scopes

• Variables

• Partner Links

• Fault Handlers and Compensation Handlers

HelloWorld Sample

HelloWorld Sample

Advanced Concepts

• Fault Handling

• Compensation

• Correlation and Async processes

• Extending WSO2 BPS

Fault Handling

• Exceptional condition that can alter the normal

processing of a business process.

• Fault need not result in an immediate process

ending.

• If a fault is not handled, it will lead to

unexpected conditions and outcomes.

• Handle faults, so that failures lead to predictable

outcomes.

Activities for Handling Faults

• Catch

• CatchAll

• Rethrow

• Throw

Catch/CatchAll

• BPEL specific runtime faults

• SOAP faults

• Standard SOAP faults

• Application specific SOAP faults

• After catching a fault

• Try to correct

• Throw a new fault

• Rethrow the fault

• Reply with a fault message

Catch/CatchAll

• Handle different types of faults in different ways.

• Multiple catch statements to catch different

types of faults.

• CatchAll activity to handle any type of Fault.

Rethrow

• If the current fault handler cannot handle the

fault

• Propagate the fault to an outer-scoped fault

handler

• Available only within a fault handler

Throw

• Indicates a problem that a business process flow

cannot handle

• Can be used any where within the process

• Can be thrown

• Standard BPEL faults

• Custom faults

• Variable can be associated to send fault

information

Fault Handlers Attached to Invoke Activity

• Handle faults specific to Invoke activity

• SOAP faults

Fault Handlers attached to Scope

• Catches faults resulting from activities within a

scope.

Global Fault Handler

• Last place for a fault to be captured.

• Faults propagate from the inner scopes to the

outer scopes

Fault Types in Invoke Activity

• Faults

• BPEL standard faults

• SOAP faults

• Failures

• Connection refused

• Service not found

Fault Handling Sample

Compensation

• Undoing the steps in business process that have

been already completed

Activities for Compensation Handling

• compensationHandler – defines the compensation

logic per each scope

• compensateScope and compensate - used to

trigger the compensationHandler.

Compensation Handling Sample

Asynchronous Invocation

• What Asynchrony is.

• Different asynchronous transport protocols

eg – JMS, SMTP, XMPP

• Modeling asynchronous behavior in WSDLs

eg – by two one-way operations

Asynchronous Invocations in BPELs

• Invoke activity to invoke the partner-service

• Receive activity to act as the call-back handler

• So how these two messages get correlated?

Message Correlation

• Building block for stateful conversations in BPELs

• Determine to which conversation a message

belongs

Message Correlation Sets

• correlationSet - defines the element(s) in

message to act as a unique-id for each message

• correlation - handles the message correlation

between each conversation

Correlation sample

Extending WSO2 BPS

• BPEL extensions

• Enable to define new BPEL activities

• peopleActivity for BPEL4People

• BPEL event listeners

• Enables to listen to events fired by BPEL engine

• Gather information for BAM

• Message exchange interceptors

• Enables to intercept through the message exchanges

• XPath extensions

Q & A