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Business Process Modeling, Management and Mining

Business Process Model and Notation

Prof. Cesare Pautasso
http://www.pautasso.info
cesare.pautasso@usi.ch
@pautasso

Human Tasks

Manual Tasks are carried out by people without using any software system

User Tasks are carried out by people interacting with the workflow engine

Messaging Tasks

Represent message exchanges between participants

Send Tasks will complete once the message is sent

Receive Tasks will wait for a message and complete once it arrives

Automated Tasks

Web Service invocations, External Software Applications

Local computations (scripts embedded within the Workflow engine)

Evaluation of business rules (e.g., to make decisions)

Control Flow Gateways

Gateways are a syntactic construct to represent branches and merges in the control flow graph

Gateways are not labeled with any "business" information (use events and activities instead)

Gateways represent decision points and can be annotated with conditions

XOR Gateway

Exclusive gateways represent sequential branches/merges in the control flow

Branch: every incoming token corresponds to at most one outgoing token (statically checked)

Merge: no synchronization is performed with multiple incoming tokens

AND Gateway

Parallel gateways represent parallel fork/joins in the control flow

Branch: a token is sent on every outgoing control flow edge

Merge: wait for a token to arrive from each incoming edge

Deadlock

The merge AND gateway will wait forever for 2 tokens, while the branch XOR gateway will never produce more than one

Lack of Synchronization

The merge XOR gateway will let through both tokens produced by the AND parallel branch

Loop

The merge XOR gateway will let through any incoming token, either from upstream A or from the outgoing XOR branch. The loop will exit once control flow reaches D.

Livelock

The loop will never exit, and whatever follows (D) the cycle in the graph will also be repeated with every iteration

Which gateway do we need?

AND merge would result in a potential deadlock

XOR merge would result in a potential lack of synchronization

OR Gateway

Inclusive gateways represent overlapping sequential/parallel branches

Branch: a token is sent on every outgoing control flow edge with a satisfied condition

Merge: wait for a token to arrive from each edge that was triggered in the inclusive branch

OR Gateway Equivalent Semantics

Can you build an equivalent control flow graph using only XOR and AND gateways?

References

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