Orchestration of an OGSI-enabled scientific
application using the Business Process Execution Language
Grids and Applied Language Theory
(GAL2003)
Ben Butchart
Wolfgang Emmerich
University College London
b.butchart@cs.ucl.ac.uk
w.emmerich@cs.ucl.ac.uk
Overview
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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
is last spacegroup ?
molpak
no
yes
collate results
loop 1..X high denisty structures
is last structure ?
dmarel
yes
no
Control logic of the distributed polymorph
prediction application
configure system
molpak
molpak
dmarel
dmarel
dmarel
molpak
dmarel
collate results
dmarel
dmarel
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
<sequence name="sequence">
<receive name="receive" partner=“user" portType="p:PolyPort"
operation="runPoly" container="request“ createInstance="yes"/>
<assign>
<copy>
<from container="request" part="atomArray"/>
<to container="molpakrequest" part="atomArray"/>
</copy>
</assign>
<assign>
<copy>
<from container="request" part="crystal"/>
<to container="molpakrequest" part="crystal"/>
</copy>
</assign>
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
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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
Workflow Engine
Compute
Service
Compute
Service
Workflow Engine
Compute
Service
After Krishnam, Wagstrom, Laszewski
GSFL: A Workflow Framework for Grid Services
Compute
Service
Compute
Service
Compute
Service
Late binding
OGSA
Registry
getBindingURL(PortType)
BPEL
Parser
Abstract
Binding
OGSA Registry
OGSA
Factory
Binding
Create instance
Molpak service
UDDI
Binding
<invoke name="invoke1"
partner="provider"
portType="mpak:MolpakPort"
operation="runMolpak"
inputContainer="molpakrequest"
outputContainer="molpakresponse
"/>
UDDI Registry
WSDL
Binding
<service
name="MolpakService">
<port>
<soap:address
location=
"http://tapas.cs.ucl.ac.uk:
8080/ogsa/services/"/>
</port>
</service>
Scalability
Workflow Engine
Workflow Engine
Compute
Service
Compute
Service
Compute
Service
Compute Service &
Workflow Engine
compute1
compute2
compute3
Compute
Service
Compute
Service
How we solve the problems
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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
GSFL
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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
BPEL
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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
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)
BPEL Engine
compute node
8.invoke
service
1.getBindingURL
(PortType)
molpak service
isntance
9.invocation
completed
Dummy Process
(blocks)
10.kill
Trader
Binding
2.getBindingURL
(PortType)
Trader
6. SGEchooseMe
(jobID,myURL)
3. Run a proxy job
(jobID, traderURL)
7. search for
instance
OGSA
Registry
SGE
Wrapper
5. runDummy.sh
(jobID,traderURL)
4. Run a proxy job
(jobID, traderURL)
SGE
Late binding: deployment descriptor
<service name="poly/PolyProviderFactoryService/poly1">
<requestFlow>
<handler type="BPELRequestHandler"/>
</requestFlow>
<responseFlow>
<handler type="BPELResponseHandler"/>
</responseFlow>
<parameter name="name" value="Polymorph process workflow"/>
<parameter name="className" value="poly.PolyProvider“
<parameter name=“bindingMechanism" value=“Registry"/>
</service>