Workflow ManagementKap. 4. Analyzing Workflows

Wil van der Aalst has copyrights to almost all figures in the following slideshow made by Lars Frank.

“Soundness” analysis can prevent logical errors:

Soundness property:

Unbounded and never ending loop error:

A petri net is bounded when there is an upper limit for tokens.

A petri net is safe when the upper limit for tokens is onefor all places = Bounded by value one.

Soundness property proof:

If a transition is replaced by a sound workflow, then the resulting workflow is also sound.

Examples of Sound nets:

Example of Sound proof:

Why is there no proof for the soundness property?

Techniques to analyze workflows:

(About the structure of the workflow. For example soundness)

(About attribute values and management of the workflow)

Deadlock illustration where both Trans1 and Trans2 want to lock(låse) Object1 and Object2:

lås1

1

lås3

1

frigiv1

1

lås2

1

lås4

1

frigiv2

1

object1 object2

Trans 2

Trans 1 Trans 1

Trans 2

Trans 1

Trans 2

slut

slut

Fairness property:

The fairness property says that if a task potentially can be executed, then it will be executed sooner or later.Does the workflow have a logical error if task2 is a “marriage” that produce “families”?

Petri-net analysis:

Reachability graph without cycles:

Reachability graph with reachable states:

Reachability graph with cycles:

(red1,green1,yellow1,safe,red2,green2,yellow2,safe)

Green

Both red

Yellow Yellow

Green

Some petri nets has Place invariants:

Place invariants = Constant calculated as the weightet sum of the tokens in each place.

Example:

man +woman + 2 * couple = 7

Performanceanalysis:

Computer simulation is the repeated execution of a process where choices are made upon various probability distributions.A Markov chain is a reachability graph with the probability of transition added to it.

Prove the soundness of the coupled e-commerce workflow?

Which e-commerce model will you re-commend in practice?

End of session

Thank you !!!Thank you !!!

Petri net Work flowfor global E-commerce transactions where the stocks are in the locations of the different suppliers.

1. Put products in the basket

Start

Timer

2. Confirm order-lines and update stocks in servers

4. Receive products from suppliers and update QUANTITY received

6. Send the rest of the products to the customer

End

3.Suppliers send products

Non confirmed order

Products

All products are received

5. Send the received products to the customer

Suborders

Canseled order

Stock rejected order

Confirmed order

OR split

Sub- Petri net of activity 2

2.1 try to confirm thenext order-line

Order-line

An-swer

Nonconfirmedorder

2.2 Supplier's servertry to confirm

order-line

More order-lines

2.3 Update Order with supplieranswer for each order-line

All answers received

Order-line

Order

Order

2.4 Send Order with confirmanswers to the Customer. If theOrder was confirmed The Timeris set and confirming Sub-ordersare send to the involvedsuppliers.

Timer Sub-orders

Confirmed Order

Stockrejectedorder

AND split

OR split

AND join

Exercise in quantitative analysis: