Web Services Flow Language

1
Web Services Flow Language

• Guoqiang Wang
• Oct 7, 2002

2
Outline

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

3
What is WSFL?

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

4
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

5
Flow Model Example
6
(No Transcript)
7
Flow Model Syntax

• Activity
• Control Links
• Transition Conditions
• Forks and Parallelism
• Join and Synchronization
• Data Links
• Service Providers

8
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

9
Flow Model Syntax
10
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

11
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

12
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

13
Flow Model Syntax

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

14
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

15
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

16
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

17
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

18
Flow Model Syntax
19
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

20
Flow Model Syntax

• Illustration
• Activities
• Join Condition
• Exit Condition

21
Flow Model Syntax

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

22
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?

23
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

24
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

25
Lifecycle Interface

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

26
Business Process Lifecycle
27
Activity Lifecycle
28
Global Model

• Interaction between service providers
• Recursive Composition
• Specify all possible interactions

29
Global Model Example
30
(No Transcript)
31
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

32
Language Description

• XML Semantics
• WSFL Schema

33
Business process modeling with WSFL
34
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