Ben Butchart Wolfgang Emmerich University College London b.butchart@cs.ucl.ac.uk

transcript

Orchestration of an OGSI-enabled scientific application using the Business Process Execution Language

Ben Butchart

Wolfgang Emmerich

University College London

b.butchart@cs.ucl.ac.uk

w.emmerich@cs.ucl.ac.uk

Grids and Applied Language Theory (GAL2003)

Overview

• How we became interested in workflow• Why we chose BPEL• A BPEL appetizer• Shortcomings of existing BPEL implementations• Shortcomings of BPEL language itself• Overcoming some problems• Comparison with GSFL• Conclusion and future work• Discussion

The Beginning…

A messy but beautiful data flow diagram

Control logic of the Polymorph prediction application (not distributed)

configure system

loop 1..29 space groups

loop 1..X high denisty structurescollate results

molpak

dmarel

is last structure ?

is last spacegroup ?

Control logic of the distributed polymorph prediction application

molpak molpak molpak

dmarel dmarel dmarel dmarel dmarel dmarel

collate results

configure system

So why BPEL ?

• WSFL and XLANG deprecated• Microsoft, IBM, BEA triumvirate powerful

market force• Submitted to OASIS for standardization• First implementations already available for

evaluation (IBM BPWS4J, Collaxa)• Do not want to diverge from standard Web

Services technology set

Instantiating SOAP message

<soapenv:Body> <runPoly xmlns="http://poly"> <ns1:atomArray xmlns:ns1="http://www…/cml2/core"> <ns1:atom elementType="H" x="3.17" y="2.43“ z="0.02"/> <ns1:atom elementType="H" x="-1.74" y="2.61" z="-0.38"/> </ns1:atomArray> <spacegroups> <spacegroupLabel>AA</spacegroupLabel> <spacegroupLabel>AB</spacegroupLabel> </spacegroups> <ns2:crystal z="1" xmlns:ns2="http://www…/cml2/core"> <ns2:scalar title="alpha" units="deg">0</ns2:scalar> <ns2:symmetry id="" spaceGroup=""/> </ns2:crystal> </runPoly> </soapenv:Body>

BPEL Example

BPEL Example

<assign> <copy> <from container="request" part="spacegroups“

query="./spacegroupLabel[position()=1]" /> <to container="molpakrequest" part="crystal"

query="./ns2:symmetry/@id" /> </copy></assign>

<invoke name="invoke1" partner="provider" portType="mpak:MolpakPort"

operation="runMolpak" inputContainer="molpakrequest"

outputContainer="molpakresponse"/>…

</sequence>

BPEL Features

• Loop and control logic• XPath query assignment• Recursive Composition• Synchronous and asynchronous

communication• Concurrent execution• Correlated messages• Event handling• Fault handling

Shortcomings of BPEL implementations

• Binding to a URL expected at deployment time

• Early implementations could not cope with OGSI extensions to WSDL

• Or properly handle imports• Dynamic creation of new process instances to

improve scalability• Steering – change process during execution

Shortcomings of BPEL language

• Need placeholder objects to support some assignments

• Data aggregation - No way to temporarily collate results

• Cannot specify mechanism for binding (WSDL, UDDI, OGSAFactory)

• Limited lifecycle interface (just receive, pick terminate)

• Verbose• Does not support peer communication

The scalability problem

After Krishnam, Wagstrom, LaszewskiGSFL: A Workflow Framework for Grid Services

Workflow Engine Workflow Engine

Compute Service

getBindingURL(PortType)

BPEL Parser

AbstractBinding

WSDLBinding

UDDIBinding

OGSA Registry

OGSA FactoryBinding

OGSA Registry

UDDI Registry

Molpak serviceCreate instance

Late binding

Scalability

Workflow Engine

Compute Service

Workflow Engine

Compute Service

Compute Service &Workflow Engine

Compute Service

compute1

compute2

compute3

How we solve the problems

• late binding: extra URL binding mechanisms• scalability: recursive composition• scalability: group binaries into single WS port type • scalability: dynamic deployment and delegation• steering: use BPEL event handling functionality• aggregation: use a dedicated web service• verbose: use GUI/XSLT

Other Web Service Workflow Languages

• WSFL and XLANG – now superseded by BPEL

• GSFL – extension to WSFL to support Grid requirements

• SWFL – another extension to WSFL • Scufl (taverna) / Freefluo

Comparison with GSFL

• recursive composition

• correlated messages

• separates data flow

• peer data flow modelling

• binding mechanism configurable

• WS standard

• cross vendor support

• fault handling and compensation

• concurrent control flow

• message part assignment

• Xpath assignment

• implementations available

• recursive composition

• correlated messages

• separates data flow

• peer data flow modelling

• binding mechanism configurable

• WS standard

• cross vendor support

• fault handling and compensation

• concurrent control flow

• message part assignment

• Xpath assignment

• implementations available

GSFL BPEL

Conclusion

• Can use BPEL for modelling grid applications – no real need for extensions

• But we need an implementation that is Grid enabled

• Might not need full implementation • We should stick with WS technology set if at

all possible

Integration with Scheduler (Sun Grid Engine)

2.getBindingURL(PortType)Trader

Binding

3. Run a proxy job (jobID, traderURL)

molpak serviceisntance

OGSARegistry

Trader

SGE Wrapper

4. Run a proxy job (jobID, traderURL)

Dummy Process(blocks)

5. runDummy.sh(jobID,traderURL)

BPEL Engine

1.getBindingURL(PortType)

9.invocation completed

6. SGEchooseMe(jobID,myURL)

10.kill

7. search for instance

8.invoke service

compute node

Late binding: deployment descriptor

Ben Butchart Wolfgang Emmerich University College London b.butchart@cs.ucl.ac.uk

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