Difference: WorkflowManagementSystem (1 vs. 7)

Main Web Site

http://wfms.forge.cnaf.infn.it

CGIW08

Simone Pellegrini, Andreas Hoheisel, Francesco Giacomini, Antonia Ghiselli: Using GWorkflowDL for Middleware-Independent Modeling and Enactment of Workflows. Submitted for the CoreGRID Integration Workshop 2008, Crete, 2008.

WaGe08 [coming]

Simone Pellegrini, Francesco Giacomini: Desing of a Petri Net-based Workflow Engine. Submitted for the The 3rd International Conference on Grid and Pervasive Computing (GPC 2008), Kunming (China), 2008.

CG08 [under reviewing process]

Simone Pellegrini, Francesco Giacomini: GWorkflowDL: A Multi-purpose Language for Scientific Workflow Enactment. Submitted for the 3rd CoreGRID Workshop on Grid Middleware, Barcellona, 2008.

Contacts

INFN Cnaf Bologna

Simone Pellegrini, Francesco Giacomini

ICGW08 [under reviewing process]

Simone Pellegrini, Andreas Hoheisel, Francesco Giacomini, Antonia Ghiselli: Using GWorkflowDL for Middleware-Independent Modeling and Enactment of Workflows. Submitted for the CoreGRID Integration Workshop 2008, Creta, 2008.

WSES08 [under reviewing process]

Simone Pellegrini, Francesco Giacomini: Desing of a Petri Net-based Workflow Engine. Submitted for the 3rd International Workshop on Workflow Systems in e-Science, Lyon, 2008.

Concepts

Workflow Engine

<workflow>
   <place ID="p1">
     <token><data><file xsd:type="xsd:string">file://home/data.dat</file></data></token>
   </place>
   <place ID="p1_jdl">
     <token><data>
        <jdl xsd:type="xsd:string">
           Type = "Job";
           JobType = "Normal";
           Executable = "/bin/cat";
           Arguments = "data.dat";
           StdOutput = "dump.txt";
           InputSandbox = {"data.dat"};
           OutputSandbox = {"dump.txt"};
           Rank = -other.GlueCEStateEstimatedResponseTime;
           Requirements = (other.GlueCEInfoHostName == "ce06-lcg.cr.cnaf.infn.it");
        </jdl></data></token>
   </place>
   <place ID="p2" />
   <transition ID="cat">
      <inputPlace placeID="p1" edgeExpression="in"/>
      <inputPlace placeID="p1_jdl" edgeExpression="jdl"/>
      <outputPlace placeID="q0" edgeExpression="out"/>
      <operation>
         <swOperation name="JobExecute" />
      </operation>
   </transition>
</workflow> 

The swOperation allows to invoke sub-workflows, which implements the particular operation. In this case, the JobExecute workflow describe (using the Petri Nets formalism) the operation to perform in order to execute a task in the gLite Grid middleware. The sequence of operation is depicted in the following figure:

and the wait_for_termination transition also invoke a sub-workflow which can be expressed (using a polling strategy) in the following figure:

Consider the following abstract workflow, it consists in the remote execution of the command: /bin/cat data.dat.

<workflow>
   <place ID="p1">
     <token><data><t1 xsd:type="ref:file">file://home/data.dat</t1></data></token>
   </place>
   <place ID="q0" />
   <transition ID="cat">
      <inputPlace placeID="p1" edgeExpression="a1"/>
      <outputPlace placeID="q0" edgeExpression="b"/>
      <operation/>
   </transition>
</workflow> 

Workflow Management System

CoreGRID

The project also aims at language interoperability, placing attention to workflow description languages and introducing language translators. The internal representation of a workflow is based on the High Level Petri Nets (HLPN) formalism due to its formal semantics and the existence of several analysis tools. The reference language of the WfMS is the Grid Workflow Description Language (GWorkflowDL) which is based on the HLPN formalism.

The fist prototype of the system have been tested with workflows accessing resources available on the Grid provided by the EGEE project, a large and relatively mature infrastucture. In particular, the execution of Grid jobs is performed by relying on the gLite Workload Management System (WMS) through its Web Service interface (WMProxy).

Papers

CGW07

Simone Pellegrini, Francesco Giacomini, Antonia Ghiselli: A Practical Approach for a Workflow Management System. In Proceedings of the CoreGRID Workshop 2007, Dresden, 2007.

Petri Nets in workflow modeling

1. the formal semantics despite the graphical nature,
2. state-based structure (as opposed to the event-based one),
3. the availability of many analysis techniques.

More suitable than Petri Nets, the High Level Petri Nets (HLPN) formalism can be used for workflow modeling. The HLPN term is used for many Petri Nets formalisms that extend the basic P/T net formalism. This includes coloured Petri Nets, hierarchical Petri Nets, and timed Petri Nets. The Grid Workflow Description Language is based on HLPN.

The Grid Workflow Descpription Language

1. a generic part, used to define the structure of the workflow, reflecting the data and control flow in the application,
2. a middleware-specific part (extensions) that defines how the workflow should be executed in the context of a specific Grid computing middleware.

The generic part of the workflow can be represented in the GWorkflowDL language as:

<workflow>
   <place ID="p1">
     <token><data><t1 xsd:type="xs:int">3</t1></data></token>
   </place>
   <place ID="p2">
     <token><data><t2 xsd:type="xs:int">2</t2></data></token>
   </place>
   <place ID="q0" />
   <transition ID="sum">
     <inputPlace placeID="p1" edgeExpression="a1"/>
     <inputPlace placeID="p2" edgeExpression="a2"/>
     <outputPlace placeID="q0" edgeExpression="b"/>
     <operation /> <!-- generic operation -->
   </transition>
</workflow> 

In the workflow there are no information about the operation associated to the Petri Net transiion T. More detailed information are provided by the concrete part of the description. A concrete operation could be the invocation of a Web Service, or the remote execution of a program or the invocation of a local routine.

The enactment process, performed by the WfMS, is responsable of mapping abstract operations -- associated to a Petri Net transisions -- to concrete operations. For example the plus operation represented in the above workflow can be mapped to a Web Service invocation as described in the following concrete workflow:

<workflow>
   <place ID="p1">
     <token><data><t1 xsd:type="xs:int">3</t1></data></token>
   </place>
   <place ID="p2">
     <token><data><t2 xsd:type="xs:int">2</t2></data></token>
   </place>
   <place ID="q0" />
   <transition ID="sum">
      <inputPlace placeID="p1" edgeExpression="a1"/>
      <inputPlace placeID="p2" edgeExpression="a2"/>
      <outputPlace placeID="q0" edgeExpression="b"/>
      <operation>
         <wsOperation wsdl="http://localhost/plus?wsdl" operationName="plus">
            <in>n1</in>
            <in>n2</in>
            <out>q1</out>
         </wsOperation>
      </operation>
   </transition>
</workflow> 

<workflow>
   <place ID="p1">
     <token><data><t1 xsd:type="xs:int">3</t1></data></token>
   </place>
   <place ID="p2">
     <token><data><t2 xsd:type="xs:int">2</t2></data></token>
   </place>
   <place ID="q0" />
   <transition ID="sum">
      <inputPlace placeID="p1" edgeExpression="a1"/>
      <inputPlace placeID="p2" edgeExpression="a2"/>
      <outputPlace placeID="q0" edgeExpression="b"/>
      <operation>
         <pyOperation operation="b = a1 + a2" />
      </operation>
   </transition>
</workflow> 

The WfMS and the EGEE/gLite Grid Middleware

-- SimonePellegrini - 19 Dec 2007