Web Services Flow Language Guoqiang Wang Oct 7, 2002

Outline What is WSFL? Flow Model Global Model Lifecycle Language Description

What is WSFL? WSFL is an XML language for the description of Web Services compositions Usage pattern composition Interaction pattern composition

Flow Model A flow model is the specification of activities and their properties, as well as the associated wiring of the activities by control links and data links

Flow Model Example

Flow Model Syntax Activity Control Links Transition Conditions Forks and Parallelism Join and Synchronization Data Links Service Providers

Flow Model Syntax Activities An activity represents a business task to be performed as a single step within the context of a business process Corresponds node in a graph Can have input, output messages

Flow Model Syntax

Control Links A control link is a directed edge that prescribes the order in which activities will have to be performed The potential control flow between activities of the business process

Flow Model Syntax Transition Conditions A transition condition is a Boolean expression that is associated with control link Each control link has a transition condition Possible follow-on activities Actual follow-on activities

Flow Model Syntax Control Links As Edges Directed “Weighted” by transition condition At most 1 control link between 2 activities Acyclic – No loops Loops are supported in a controlled manner

Flow Model Syntax The Origin of Flow Dynamics Output actual data values Input Control links

Flow Model Syntax Forks And Parallelism A fork activity is an activity that has more than one outgoing control link Parallelism: when more than 1 transition condition is true

Flow Model Syntax Join and Synchronization Synchronize parallel work by join activities A join activity is an activity that has more than one incoming control link Default behavior: defer the decision until all parallel work that can finally reach the join activity has actually reached it

Flow Model Syntax Join conditions A join condition is a Boolean expression associated with a join activity Default behavior Weaker semantics of synchronization As soon as the truth-value of a join condition is known, the associated join activity can start

Flow Model Syntax Start and End Activities Start activities End activities Conceptually each activity has a join condition associated  activity can be started whenever its join condition is fulfilled Overall flow done

Flow Model Syntax

Exit Conditions An exit condition is a Boolean expression to determine whether or not the execution of the activity completed Distinguishes 2 events Events completed successfully Events interrupted for whatever reason

Flow Model Syntax Illustration Activities Join Condition Exit Condition

Flow Model Syntax Loops An activity is iterated until its exit condition is met Many problems arise for the use of loops

Flow Model Syntax B is a join node, initially TC of CL from D  B unknown C completes second time, control flow to E again? What if E still running for its first invocation?

Flow Model Syntax Data Links A data Link specifies that its source activity passes (some of) data to the target activity Data always flows along control links

Flow Model Syntax Service Providers The expected behavior of a potential business partner Service provider type Locator a specification of how to find a specific service provider

Lifecycle Interface Each flow model has a port type allows managing the lifecycle of instance of it Call Spawn Resume Suspend Inquire Terminate

Business Process Lifecycle

Activity Lifecycle

Global Model Interaction between service providers Recursive Composition Specify all possible interactions

Global Model Example

VS Global Model VS Flow Model Flow Model Executable business model Activity as flow unit Global Model Business Collaboration Service Provider (Business partner) as flow unit

Language Description XML Semantics WSFL Schema

Business process modeling with WSFL

References IBM -- Web Services Flow Language (WSFL 1.0), Prof. Dr. Frank Leymann, IBM Software Group, May 2001 The Web services insider, James Snell, Software Engineer, Emerging Technologies, IBM, July 2001 Internet-Based Workflow Management: Towards a Semantics Web. Dan.C.Marinescu. Wiley, 2002