Constraint-Based Workflow Models Change Made Easy! Maja Pesic Helen Schonenberg Natalia Sidorova Wil van der Aalst Eindhoven University of Technology

support control flexibility Workflows, what people want...

Classical trade-off "do whatever you want but get no support" "support but no flexibility"

Three types of flexibility Defer (decide to decide later) –deferred choice –late binding (e.g., worklets) Change (decide to change model) –ad-hoc change –evolutionary change Deviate (decide to ignore model) –skip –redo –swap

Typical approach: procedural language + change Changes: ad-hoc (one instance) and evolutionary (whole process). Attempts to combine the best of both worlds. Supported by smart/mature systems like ADEPT. Problems: –Users cannot model! –Difficult to support. dynamic change bug

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An alternative approach based on constraints...

Basic idea Declarative notation (e.g., ConDec, DecSerFlow) LTL semantics

Example: "existence response" OK: –[ ] –[A,B,C,D,E] –[A,A,A,C,D,E,B,B,B] –[B,B,A,A,C,D,E] –[B,C,D,E] NOK –[A] –[A,A,C,D,E]

Example: "response" OK: –[ ] –[A,B,C,D,E] –[A,A,A,B,C,D,E] –[B,B,A,A,B,C,D,E] –[B,C,D,E] NOK –[A] –[B,B,B,B,A,A]

Example: "precedence" OK: –[ ] –[A,B,C,D,E] –[A,A,A,C,D,E,B,B,B] –[A,A,C,D,E] NOK –[B] –[B,A,C,D,E]

DECLARE

Model with constraints –(C.1) Always start with activity register client data. –(C.2) Activity bill must be executed at least once. –(C.3) Every room service must be billed. –(C.4) Every laundry service must be billed. –(C.5) If the client checks-out- she/he must be charged. –(C.6) Sometimes it is recommended that additional cleaning is also be billed. (---optional---)

constraints can be: –mandatory imposed by DECLARE can be fulfilled or temporarily violated –optional used as warnings for users can be fulfilled or temporarily violated or permanently violated at the end of the execution all mandatory constraints have to be fulfilled

(a) initial state (b) after "register client data" (c) after "room service"(d) after "bill"

Change Made Easy.... Flexibility

Three types of flexibility revisited Defer (decide to decide later) Change (decide to change model) Deviate (decide to ignore model)

Defer (decide to decide later) Try to model this is your favorite business process modeling tool!

Change (decide to change model) pray to become holy Jane: curse, curse, pray, curse Mike: pray, become holy, pray Tracy: become holy, pray

Deviate (decide to ignore model) soft versus hard constraints (levels/warnings) optional

Conclusion DECLARE supports different types of flexibility in a natural way: –Defer (decide to decide later) –Change (decide to change model) –Deviate (decide to ignore model) Avoids problems such as the dynamic change bug and can deal with situations where users will not change models. Fully implemented and integrated with ProM and YAWL. See vdaalst.com for papers and is.tm.tue.nl/staff/mpesic/declare.htm for software.