Checking Properties of Adaptive Workflow Nets

1. Checking Properties of Adaptive Workflow Nets K. van Hee, I. Lomazova, O. Oanea, A. Serebrenik, N. Sidorova, M. Voorhoeve Program Systems Institute of the Russsian Academy of Science

2. Overview Workflow (WF) nets and proper termination. Problems with fixed structure of netsespecially exception modelling. EWF nets: WF nets with exception transitions. AWF (adaptive WF) nets: nesting. Verification of AWF nets.

3. i a r c b q d f p Workflow net Petri net with initial (source) and final (sink) place. All other nodes on directed path from source to sink. Marking: e.g. [p]+2[q] Enabled, firing Reachability: Always: Soundness: every marking reachable from [i] can reach [f] ([i] sat AG EF [f])

4. i f Problem: modelling exceptions Typical sound WF net with parallelism (normal flow): superfluous firing needed In one thread an exception may occur. Soundness should be preserved. The other thread should be interrupted. Model becomes unfeasible.

5. i f Reset arcs Reset arc empties all places in region. Improves modeling, makes analysis worse. No specific reaction to exceptions. Problem with adaptivity in general,due to fixed structure!

6. i f EWF nets Labelled exception (sink) transitions;upon firing an exception, the net is terminated. EWF net is sound iff

7. final(v) init(n) v v b b e(v) b b b e AWF nets: definition n Adaptive WF (AWF) net: coloured EWF net. Arcs and transitions arelabeled with expressions n: an EWF net

8. AWF nets: allowed expressions We presuppose a set of “standard”sound EWF nets (domain dependent). • In-arc expressions: • -b: black, • v (variable): net Out-arc expr’s built from: std nets, variables, operators e.g.: . (seq. composition), + (choice), || (parallel composition) Transition expressions (guards): - none, - e(v) (eexceptionlabel), - final(v), init(n||m).k v final(v)

9. final(v) init init(n+m) + v m v b b e(v) v b b n b e(v) t e AWF net firing rules Transitions in the AWF net can fire, producing black or net tokens. marked net tokens final init +m e e AWF net and token net can fire independently or synchronized on exception label or upon token net having reached the final state.

10. v init(n) v v.m final(v)final(w) e(w) init(c) w init(c) w c: Adaptivity Modeling hospital admission; standard cure n. Monitor; if needed extend current cure with m. e: extension needed.

11. final(v) b b init(n) v b b b e b Circumspectness AWF net: Sound, but can not react to exception e in token net n. (not circumspect) n: AWF net Nis circumspect:every exception e of token netcan synchronize in any state of N.

12. final(v) init init(n+m) + v m v b b e(v) v b b n b e(v) t e Circumspect AWF net Net can synchronize with ebefore and after firing of t.

13. v. m v Verification of AWF nets Colour sets of AWF nets are infinite, so no direct model checking possible. Abstract interpretation a:map token colours tosets of exception labels. The set of library net exception labels is finite! Theorem: AWF net N sound iff all states reachable in a(N) by nonexceptional firings canterminate without synchronising on exceptions. Similar result for circumspectness.

14. Conclusions EWF nets: WF nets with exceptions. AWF nets: EWF nets with nesting (e.g. reaction to exceptions). Proper termination and circumspectness of AWF nets can be checked. Extensions: Synchronisation without termination.Checking other temporal properties. Thank you for your attention! department of mathematics and computer science