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

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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

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

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

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

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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.

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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

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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?

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