1 Grid Workflow Description Language ----------- __Up to date information about the Grid Workflow Description Language is available at the {link:GWorkflowDL software development site|http://www.gridworkflow.org/kwfgrid/gworkflowdl/docs/}__ Current GWorkflowDL examples are available at {link:myExperiment.org|http://www.myexperiment.org/workflows/search?query=GWorkflowDL} ----------- The Grid Workflow Description Language ([GWorkflowDL]) is being developed in the context of the [K-Wf Grid] and the [CoreGRID] projects as an extension of the existing Grid Job Definition Language ([GJobDL]), an XML-based language that makes use of the formalism of [Petri net]s in order to describe the dynamic behaviour of distributed Grid jobs. The GJobDL was developed for the [Fraunhofer Resource Grid]. The advanced GWorkflowDL has the following features: 1. In principle, the rules of coloured [Petri net]s apply \[Jensen:94\]. 1. Definition of transitions: may have reference to an [OWL] description of \{operation, WSClassOperation, list of WSOperations, WSOperation\}. 1. A transition may also refer to a whole sub net -> hierarchical approach. 1. Edges link transitions to input places and output places. Edge expressions are used to relate input places to a specific parameter of a Web Service operation. 1. Definition of places: may have reference to an OWL description of data or parameters for type checking. 1. Transitions may be annotated with conditions. Conditions could be expressed by XPath queries, by Web Service operations or other (user-defined) modules that return a Boolean value. 1. Tokens are placed on places and contain high-level control information (e.g., true or false) or data related to the input and output parameters of the Web Service operations. Tokens store the state of the workflow. One implementation of a [Workflow Engine] for the [GWorkflowDL] is the so-called [GWES] (Grid Workflow Execution Service). 1.1.1 GWorkflowDL XML Schema Figure \[GWorkflowDL0.4\] represents the XML Schema of the GWorkflowDL version 0.4. The root element is called ~~<workflow>~~, which contains the optional element ~~<description>~~ with a human-readable description of the workflow, and several occurrences of the elements ~~<transition>~~ and ~~<place>~~ that define the Petri net of the workflow. The element ~~<transition>~~ contains a child element ~~<KWfGridExtension>~~ which represents the special K-Wf Grid mapping of transitions onto several levels of abstraction regarding Web Service operations. The child elements ~~<inputPlace>~~ and ~~<outputPlace>~~ define the edges of the net. {image:gworkflowdl_0_4.gif} ~~__Figure \[GWorkflowDL0.4\]:__ Graphical representation of the XML Schema of the GWorkflowDL version 0.4. Legend of the symbols: ?=0..1; *=0,1,2,...; +=1,2,3,...~~ The following XML code shows the complete XML Schema of the GWorkflowDL version 0.4. {code:XML} <?xml version = "1.0" encoding = "UTF-8"?> <xs:schema xmlns:xs = "http://www.w3.org/2001/XMLSchema"> <xs:annotation> <xs:documentation> Copyright K-Wf Grid project team (http://www.kwfgrid.net/) 2005 Written by Andreas Hoheisel, Hans-Werner Pohl, and Tilman Linden Fraunhofer FIRST (http://www.first.fraunhofer.de/) </xs:documentation> </xs:annotation> <xs:element name = "workflow"> <xs:complexType> <xs:sequence> <xs:element ref = "description" minOccurs = "0"/> <xs:choice minOccurs = "0" maxOccurs = "unbounded"> <xs:element name = "transition"> <xs:complexType> <xs:sequence> <xs:element ref = "description" minOccurs = "0"/> <xs:element name = "inputPlace" type = "placeRef" maxOccurs = "unbounded"/> <xs:element name = "outputPlace" type = "placeRef" maxOccurs = "unbounded"/> <xs:element name = "KWfGridExtension" minOccurs = "0"> <xs:complexType> <xs:sequence> <xs:element name = "condition" type = "xs:string" minOccurs = "0" maxOccurs = "unbounded"/> <xs:element name = "operation" minOccurs = "0"> <xs:complexType> <xs:sequence> <xs:element name = "WSClassOperation" minOccurs = "0"> <xs:complexType> <xs:sequence> <xs:element name = "WSOperation" minOccurs = "0" maxOccurs = "unbounded"> <xs:complexType> <xs:attribute name = "selected" default = "false" type = "xs:boolean"/> <xs:attribute name = "name" type = "xs:string"/> <xs:attribute name = "owl" type = "xs:string"/> </xs:complexType> </xs:element> </xs:sequence> <xs:attribute name = "name" type = "xs:string"/> <xs:attribute name = "owl" type = "xs:string"/> </xs:complexType> </xs:element> </xs:sequence> <xs:attribute name = "name" type = "xs:string"/> <xs:attribute name = "owl" type = "xs:string"/> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> </xs:element> </xs:sequence> <xs:attribute name = "ID" use = "required" type = "xs:ID"/> </xs:complexType> </xs:element> <xs:element name = "place"> <xs:complexType> <xs:sequence> <xs:element ref = "description" minOccurs = "0"/> <xs:element name = "token" minOccurs = "0" maxOccurs = "unbounded"/> </xs:sequence> <xs:attribute name = "ID" use = "required" type = "xs:ID"/> </xs:complexType> </xs:element> </xs:choice> </xs:sequence> </xs:complexType> </xs:element> <xs:complexType name = "placeRef"> <xs:attribute name = "placeID" use = "required" type = "xs:string"/> <xs:attribute name = "edgeExpression" type = "xs:string"/> </xs:complexType> <xs:element name = "description" type = "xs:string"/> </xs:schema> {code} 1.1.1 Example Figure \[PetriNet\] shows the graphical representation of a Petri net-based workflow description that contains two operations (weatherModel, and visualisation). The data that is available is represented by the token on the place "begin". The following code snippet shows the corresponding XML description of this workflow. The first transition ~~weatherModel~~ has been mapped onto a concrete Web Service operation while the second transition ~~visualisation~~ is still on an abstract level. {image:PetriNetWeather_small.jpg} ~~__Figure \[PetriNet\].__ The graphical representation of a simple, Petri-net-based workflow description.~~ {code:XML} <?xml version = "1.0" encoding = "ISO-8859-1"?> <workflow xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation = "http://www.gridworkflow.org/fhrg/gworkflowdl_0_4.xsd"> <description>example workflow involving a weather model and a visualisation of the output data</description> <place ID = "begin"> <token>gridftp://fhrg.first.fraunhofer.de/data/mm5input.dat</token> </place> <place ID = "end"/> <!-- transition related to a specific web service operation --> <transition ID = "weatherModel"> <description>weather model</description> <inputPlace placeID = "begin" edgeExpression = "input"/> <outputPlace placeID = "weatherModelOutput" edgeExpression = "output"/> <KWfGridExtension> <operation name = "weatherModel" owl = "weatherModel.xml"> <WSClassOperation name = "MM5" owl = "mm5.xml"> <WSOperation name = "mm5@first" owl = "http://fhrg.first.fraunhofer.de/ws/mm5/calc"/> <WSOperation name = "mm5@cyfronet" owl = "http://agh.edu.pl/ws/mm5/calc"/> <WSOperation name = "mm5@iisas" owl = "http://savba.sk/ws/mm5/calc" selected = "true"/> </WSClassOperation> </operation> </KWfGridExtension> </transition> <place ID = "weatherModelOutput"/> <!-- transition related to an abstract operation that is not defined yet --> <transition ID = "visualisation"> <description>Visualisation of weather data</description> <inputPlace placeID = "weatherModelOutput" edgeExpression = "input"/> <outputPlace placeID = "end" edgeExpression = "output"/> <KWfGridExtension> <operation name = "weatherVisualisation" owl = "weatherVisualisation.xml"/> </KWfGridExtension> </transition> </workflow> {code} 2008-12-05 14:27:45.315 2005-05-31 17:45:10.74 Tue May 31 17:50:45 CEST 2005 Tue May 31 17:50:03 CEST 2005