1

AUTOCHEM (ANR-07-BLAN-0323)

Decentralized Approach for Execution of Composite Web Services using the

Chemical Paradigm

Hector Fernandez, Thierry Priol and Cedric Tedeschi

2

Context

• Service oriented computing

• Service composition expressed as workflow

– Workflow execution

• Centralized Workflow execution:

• A single coordinator node.

• The composite web service will be executed in this node.

• Responsible for coordination of all data and control flow between the web services.

➔ Problems [Alonso et al., 1997][Chafle et al., 2004]:

• Scientific issues: poor scalability, communication and performance bottlenecks.

• Societal issues: privacy

Intr

od

uct

ion

3

Objectives

• Ensure an execution of composite services:

• Decentralized

• Dynamic

• Autonomic

• Loose coupling (coordination mechanism)

Intr

od

uct

ion

4

“Nature-inspired metaphors have been shown to be of high interest for service coordination.”

[Viroli et al., 2009]

5

Chemical Programming Model• A program can be seen as a chemical solution:

• Data: “floating” molecules in the solution.

• Computation: chemical reactions between the molecules.

• Implicit parallelism and autonomy of reactions until inertia.

• Data structure: Multiset.

• Containing all data molecules.

• Reaction rules re-writing the multiset.

• Pioneered by Gamma (General Abstract Model for Multiset Manipulation) [Banâtre et al., 1990].C

hem

ical

Pro

gra

mm

ing

Par

adig

m

6

High-Order Chemical Language (HOCL)• The High-Order Chemical Language, HOCL [Banâtre et al., 2006], extension of Gamma.

• Reaction rules apply on reaction rules.

• Every entity is a molecule in the multiset.

• Autonomic behaviors.

• Dynamic (runtime).

• Example:

• A reaction rules is written

replace-one P by M if C

where P is a pattern which matches the required molecule, C is the reaction condition and M the result of the reaction.

Ch

emic

al P

rog

ram

min

g P

arad

igm

7

Decentralized Composite Web Services Execution using a Chemical Paradigm

8

Architecture overview

• Nodes communicating through a persistent and fault-tolerant shared address space.

• Composite web service is executed in a fully decentralized manner.

• Workflow is executed in parts corresponding with each web service

• Data and control transfer through the shared address space.

• Loose coupling among web services.

• Each node is co-responsible of the execution.

Dec

ent r

aliz

ed C

om

po

site

Web

Ser

vice

s E

xecu

tio

n

usi

ng

a C

hem

ical

Pa r

adig

m

9

Building Block: Chemical Web Service

The architecture is composed of:

• Chemical web services (ChWSes), a chemical encapsulation of a web service.

• Service invocation

• Storage space (Contains part of multiset)

• Chemical engine– HOCL interpreter (Chemical workflow engine)

Bu

ildin

g b

lock

Dec

ent r

aliz

ed C

om

po

site

Web

Ser

vice

s E

xecu

tio

n

usi

ng

a C

hem

ical

Pa r

adig

m

10

Architecture• Multiset, dynamic and decentralized coordination mechanism.

– Acts as a shared address space containing both control and data flows.– ChWSes communicate through the multiset. (reading and writing)– Physically distributed over ChWSes storage spaces.

•

• Multiset mirrors DSM's (Distributed Shared Memory) behavior.

Arc

hit

e ctu

reD

ecen

t ral

ized

Co

mp

osi

te W

eb S

ervi

ces

Exe

cuti

on

u

sin

g a

Ch

emic

al P

a rad

igm

11

Chemical Workflow Definition

In a classical workflow definition

• Executable languages like BPEL [OASIS, 2007], XPDL [WfMC, 2008] or YAWL [Van der Aalst et al., 2005].

• All data and control dependencies in the same file.

• Made to be executed in a centralized way.

In a chemical workflow definition

• Workflow definition using chemical expressions.

• Distributes data and control dependencies to each ChWS.

• Executes in parts a workflow in each ChWS.

Bu

ildin

g b

lock

Dec

ent r

aliz

ed C

om

po

site

Web

Ser

vice

s E

xecu

tio

n

usi

ng

a C

hem

ical

Pa r

adig

mD

ecen

t ral

ized

Co

mp

osi

te W

eb S

ervi

ces

Exe

cuti

on

u

sin

g a

Ch

emic

al P

a rad

igm

Multiset

12

Chemical Representations for Workflow

• Express all data and control dependencies (reaction rules and molecules).

• We use the High-Order Chemical Language (HOCL)

• The whole solution represents the multiset containing all information.

• The solution itself is composed of as many sub-solutions as ChWSes.

Bu

ildin

g b

lock

Dec

ent r

aliz

ed C

om

po

site

Web

Ser

vice

s E

xecu

tio

n

usi

ng

a C

hem

ical

Pa r

adig

mD

ecen

t ral

ized

Co

mp

osi

te W

eb S

ervi

ces

Exe

cuti

on

u

sin

g a

Ch

emic

al P

a rad

igm

13

Chemical rules for distributed execution

• Independent from any chemical workflow representation.

• Local chemical engines use these chemical rules.

• Two sets of chemical rules:

• Control and data transfer among ChWSes (MR_transfer).

• Execution of the workflow step by step (MR_invoke).

Dec

ent r

aliz

ed C

om

po

site

Web

Ser

vice

s E

xecu

tio

n

usi

ng

a C

hem

ical

Pa r

adig

m

14

Example

15

Service2

Service3

Service4Service1

SynchronizationParallel

16

• Workflow will be executed in parts.

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

More complex examples

36

Despatch police

Despatch ambulance

Transfer patientEmergency request

Synchronization mergeMulti choice

37

Synchronization mergecontrol dependencies

Multi-choicecontrol dependencies

Data dependenceData dependence

38

Conclusion

• Demand for more decentralized and dynamic interaction schemas.

• Chemical model is well featured for decentralized workflow execution.

• Our proposal: High-level decentralized coordination mechanism.

• Decentralized Architecture:– Chemical web services working as local engines.– Distributed Multiset

– Data and control dependencies– Temporal composition

• A High-order chemical language for composite web services:– Concepts for decentralized coordination.– Autonomic behavior

Su

mm

a ry

39

Future Work

• Decentralized workflow coordination for composite web services (Chemical engines).

• Implementation of a prototype (on-going work).

• Autonomic behaviour in decentralized workflow execution.

Su

mm

a ry

40

Questions ?