Business Process Modeling, Management and Mining
Business Process Model and Notation
Prof. Cesare Pautasso
http://www.pautasso.info
[email protected]
@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?