DecSerFlow Towards a Truly Declarative

Service Flow Language

Wil van der Aalst & Maja PesicEindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

w.m.p.v.d.aalst@tue.nl

Invited talk 3rd International Workshop onWeb Services and Formal Methods8 September 2006, Vienna, Austria

Outline

1. Classical approaches• BPEL2PN• PN2BPEL

2. DecSerFlow• Language• Graphical notation and LTL semantics• Implementation and application

(specification and enactment)

3. Using DecSerFlow for process mining

4. Conclusion

Classical approaches

BPEL2PN

PN2BPEL

1. Formal languages (Petri nets, LTS, YAWL)

2. Graphical languages(BPMN,UML-AD)

Industry standards:1. BPEL2. (abstract) BPEL3. WS-CDL4. etc.

BPEL2PN• Many translations are available, cf.

– S. Hinz, K. Schmidt, and C. Stahl. Transforming BPEL to Petri nets. BPM 2005.

– C. Stahl. A Petri net semantics for BPEL. Technical Report 188, Humboldt Universität zu Berlin, June 2005.

– etc.– C. Ouyang, W.M.P. van der Aalst, S. Breutel, M. Dumas, A.H.M. ter

Hofstede, and H.M.W. Verbeek. Formal semantics and analysis of control flow in WS-BPEL. Technical Report BPM-05-13, BPMcenter.org, June 2005.

• Focus on analysis, i.e., verification of various properties.• Our approach is implemented in BPEL2PNML and

WofBPEL.• cf. BEST (Berlin-Eindhoven Service Technology)

program also involving tools such as BPEL2PN, LOLA and FIONA

Example

Corresponding Petri net

PN2BPEL

• Joint work with Kristian Bisgaard Lassen.• Few people have been working on this.• Purpose: Generating readable BPEL code

(otherwise it has no purpose).• Implemented in WorkflowNet2BPEL4WS and

ProM.• Not complete, but extendible.• Work with Chun Ouyang, Marlon Dumas, et al.

(QUT) on using concepts in context of BPMN.

Basic idea

• Discover WF-net like components.

• Look for specific patterns that can easily be mapped onto BPEL (sequence, pick, switch, while, flow, etc.).

• Allow for ad-hoc extensions and re-use these.

4 types: PP, TP, PT, and TT components

Sequence

Flow

•acyclic•explicit choice•well-structured

Example

Fold sequence

Fold switch

Fold sequence

Fold sequence (2x) and pick (2x)

Final step: fold flow

Tool support: WorkflowNet2BPEL4WS and ProM

Empirical case study: 100 Protos• Different student projects.• Size of models: 23.66 places and 26.54 transitions.

• Reductions:

DecSerFlowTowards a Truly Declarative

Service Flow Language

joint work with Maja Pesic (TU/e)

Problems

• Tendency to over-specify.

• Focus on execution rather than "contractual" side.

Proposal• A more declarative approach

– Graphical– Executable– Analysis support (both design and run-time)

Basic idea

A B

DecSerFlow notation LTL semantics

LTL

Small example

1. Existence formulas

0

A

2..*

A

3..*

A

N..*

A

0..2

A

0..N

A

0..1

A

2

A

N

A

1

A

N..*

A

0..N

A

N

A

A

1..*

2. Relation formulas

A B

A B

A B

A B

A B

A B

A B

A B

A B

A B

A B

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]

A B

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]

A B

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]

A B

Combinations

A B A BA Band =

A B A B A Band =

co-existence

succession

3. Negation formulas

A B

A B

A B

A B

A B

A B

A B

A B

A B

A B A B

Example: "neg succession"

• Not the logical negation!• OK:

– [ ]– [A,C,D,E]– [A,A,A,C,D,E]– [B,B,A,A,C,D,E]– [B,C,D,E]

• NOK– [A,B]– [B,A,A,C,D,E,B]

A B

A B

A B A B

or

Using DecSerFlow

• Nature of model:– Global model (choreography model), i.e., interactions are

described from the viewpoint of an external observer who oversees all interactions between all services (non-executable specification of a contractual nature).

– Local model, i.e., the DecSerFlow model is used to specify, implement, or configure a particular service.

• Use:– Analysis of both global and local models.– Comparing global and local models.– Monitoring global and local models (conformance).– Enactment of local models.

Enactment

• A Büchi automaton typically assumes traces infinitely visiting an accepting state. There are several ways to address this. We use the approach proposed by Dimitra Giannakopoulou and Klaus Havelund to check finite traces.

• We can color the constraints green (in accepting state), yellow (accepting state can still be reached), or red (accepting state cannot be reached anymore).

Implementation (ConDec)

• Implementation on top of YAWL and ProM.• Editor (with facilities to extend language) has been

implemented.• Initial experiments with enactment service.• Plans to link editor with LTL checker in ProM.

YAWL

Prom

interface B

Editor

Add your own constraints!

Using DecSerFlow for process mining

curse prayresponse

Thanks to Ton Weijters, Boudewijn van Dongen, Ana Karla Alves de Medeiros, Anne Rozinat, Christian Günter, Eric Verbeek, Ronny Mans, Minseok Song, Laura Maruster, Huub de Beer, Peter van den Brand, Jan Mendling, Andriy Nikolov, Jianmin Wang, Lijie Wen,

Irene Vanderfeesten, Mariska Netjes, Steffi Rinderle, Walid Gaaloul, Gianluigi Greco, Antonella Guzzo, Maja Pesic, etc. etc.

Overview: Process mining

web servicesservice flow

processmodel

eventlogs

specifies global model

discovery

records events, e.g.,

via SOAP messages

specifies/implements local model

supports/controls

extension

conformance

Discovery

• Based on an event log a model is constructed without a-priori information.

• Not just the control-flow, cf. the social network miner.

• ProM examples: alpha algorithm, heuristics miner, multi-phase miner, genetic miner, etc.

web servicesservice flow

processmodel

eventlogs

specifies global model

discovery

records events, e.g.,

via SOAP messages

specifies/implements local model

supports/controls

extension

conformance

DecSerFlow

Alpha miner

Other examples

Export to CPN Tools, PNML, ARIS, EPC Tools, YAWL, Netminer, etc.

Conformance

• The log is compare with some a-priori model, the model can be a Petri net, EPC, data model, logical/temporal property, etc.

• ProM examples: conformance checker and LTL checker

web servicesservice flow

processmodel

eventlogs

specifies global model

discovery

records events, e.g.,

via SOAP messages

specifies/implements local model

supports/controls

extension

conformance

DecSerFlow

Examples

Extension

• An existing model is enriched with additional knowledge extracted from log.

• ProM examples: decision miner, staff assignment miner, performance analyzer, etc.

web servicesservice flow

processmodel

eventlogs

specifies global model

discovery

records events, e.g.,

via SOAP messages

specifies/implements local model

supports/controls

extension

conformanceDecSerFlow

Examples

Export to CPN Tools!

Conformancein webservices in a classical setting(abstract BPEL + SOAP messages)

<receive …createInstance=”YES”><correlations/></receive>

<invoke …inputVariable = …outputVariable = ...><correlations/></invoke>

<invoke …inputVariable = … ><correlations/></invoke>

<receive …variable = … ><correlations/></receive>

(MT,PI)

<reply … >variable = …</receive>

abst

ract

BP

EL

SO

AP

Mes

sage

s

SO

AP

Mon

itor/

Cor

rela

tor

(MT,PI)(MT,PI)(MT,PI)(MT,PI)(MT,PI)

...

Event log

A

E

G

D

H I

J

K

M

L

C

B

G

F

(MT,PI)

(MT,PI)

(MT,PI)

Petri net

Conformance checking!

Info

rmat

ion

Sys

tem

Conformance?

Conclusion

• Classical approaches:– BPEL2PN: mainly for analysis purposes. – PN2BPEL: also as an example for BPMN2BPEL, etc.

• DecSerFlow– Graphical notation, LTL semantics, extendible.– Linked to YAWL and ProM.

• Similar to ConDec aiming at supporting autonomous (groups of) workers.

• Interesting links between groupwork and services.

Relevant WWW sites

• http://www.processmining.org

• http:// promimport.sourceforge.net

• http://prom.sourceforge.net

• http://www.workflowpatterns.com

• http://www.workflowcourse.com

• http://is.tm.tue.nl/

• http://is.tm.tue.nl/staff/wvdaalst