Lecture 7: DCR Graphs III

Question 1

Spawn relation

Answer 1

• Spawn isused to create new instances of a process, only works for multiple-instanceprocesses
• A spawnedsubprocess creates new copies of all the events and relations in the subprocess

Question 2

Data Dependencies

Answer 2

• Events encode “state of affairs” ofan activity
• On top of execution, they carryinformation collected in the decision-making process
• Relations enable/disable furtherevents depending on data acquired via events

Question 3

Temporal Dependencies

Answer 3

• Conditions and responses mightdefine temporal dependencies between events
• X-timed response: “The execution of this activity has to be done within xtime units”
• X-time condition: “The execution of this activity is possible after x timeunits”
• Performing activities on time determineswhether the graph is accepting or not

Question 4

Why would we make a model of a process?

Answer 4

• To understand the process
• For communication (say, between managers)
• For process optimization
• For education
• For requirements specification
• For executing outright

Question 5

3 types of correctness in business processes

Answer 5

• Compliance (semantic correctness)
• Soundness (behavioral correctness)
• Syntax conformance (structuralcorrectness)

Question 6

Syntax conformance

Answer 6

• Focus on proper use of language abstractions
• Key: does it “read well”?
• Typically controlled via modelling tool/compiler
• Common errors
• Unconnected relations
• Missing variables
• Wrong timestamps

Question 7

Soundness

Answer 7

Does my model have structuralerrors?

• Does it ever terminate?
• Does it ever get an accepting state?
• Does it generate circular dependencies (deadlocks)?

Question 8

Soundness – Termination

Answer 8

• A trace is accepting, when there areno pending activities to be executed
• Trace length: the number ofactivities executed so far
• A process is non-terminating, if for any trace of length N, the execution of anactivity generates a non-accepting trace, for any N

Question 9

Soundness: The nullprocess

Answer 9

When there is no process in place, it points to nothing, no end to the process

!avoidcircular dependencies by adding additional activities

Question 10

Deadlocks

Answer 10

• There is a reachable state with no enabled activities, and there is at least one pending activity
• A DCR graph is deadlock free only if for any execution there is either an enabled event or no included required responses

Question 11

Liveness

Answer 11

• Deadlock-freedom guarantees that wewill not get stuck, but it does not say that we will do what we require
• Livelock: for all states reachablefrom the current state, there exists an enabled event and at least one includedpending event that never gets excluded or enabled
• A DCR graph is livelock free only ifin every execution it is always possible to continue along an accepting run (i.e.eventually execute or exclude any of the pending responses)