Lectures 5,6 – Workflows and Internet Process Coordination

1. Lectures 5,6 – Workflows and Internet Process Coordination • Middleware: the glue for network computing • Workflows and Internet Workflows • Enabling Technologies • Static/Dynamic workflows • Tasks and Events • Transition Systems • Workflow Patterns • Liveness • Deadlocks

3. Workflows • Informal definition. • Traditional applications: • Office automation and document processing • Factory automation • Business • Internet workflows, iWM. • Examples • Service grids • Computational grids

4. Enabling technologies

5. Areas involved in iWM

8. Lifecycle of a workflow • Creation – process definition • Process verification • Cases • Workflow enactment • The Workflow Management Coalition • Multibillion $ industry • Workflow Reference Model

10. Static/dynamic workflows • Static workflows • Dynamic workflows • Exception handling • Reversibility.

12. Workflow enactment • Case: a particular instance of a workflow • Workflow enactment engine performs a coordination function • Tasks/Activities and Events.

15. Transition systems • A directed graph: • Nodes the states of the system • Edges events • Two distinguished states: • Initial state – no incoming edge • Goal/termination state – no outgoing edge • Example: laptop assembly. States labeled by the events causing the transition.

17. Algorithm to construct the transition system from the event-task graph • 1. Construct the set of E of individual events: E={1,2,3,4,5,6,7,8,9} • 2. Split it into equivalence classes based upon the causality relationship: E1 = {1,2,3,4,9} E2 = {1,5,6,7,8,9} The two sets are not disjoint!!

18. Algorithm to construct the transition system from the event-task graph • 3. Add to E all feasible combinations of events. Each feasible combinations contains one event from each class. Example: [2,5], [3,5] are feasible combinations [2,3] is not a feasible combination

19. Algorithm to construct the transition system from the event-task graph • 4. Construct the set of states S. • Initially S contains only the initial state. • Construct the set of all events feasible in that state. • For each event in that state label the state reachable when the event occurs. • Add the new state to S • Repeat the process for every state in S.

20. Choices

21. Liveness

22. Basic workflow patterns • Sequence • AND-split • Synchronization • XOR – spli • XOR – merge • OR – split • Multiple merge • Discriminator • N out of M join • Deferred choice

24. Resources and deadlocks

25. Agents and workflow enactment • Hybrid systems: some tasks carried out by computers, others by humans. • Why use agents for workflow enactment?