Workflow Process Definition Interface — xml process Definition Language Change History

— XML Process Definition Language

Version 1.0 – Editor: Roberta Norin (robertan@attbi.com).

Added processContent=”lax” attribute to specification of SchemaType, ExtendedAttribute, and Xpression.

Changed URI references in the sample workflow to point to documents on the wfmc.org web site.

Changed SubFlow Id’s in sample workflow to refer to Workflow Process by Id rather than Name.

Version 0.10 -- Editor: Roberta Norin (robertan@attbi.com ). Contributors: Seth Osher (Intuitive Products International Corp.) and Robert Shapiro (Cape Visions).

Removed InlineBlock and BlockName elements from schema, from content of ransitionRestriction. Removed BlockName element, and from specification.

Added ActivitySets and BlockActivity to schema and to specification

Removed maxOccurs attribute from Activities in schema.

Added Deadline element to schema and specification.

Integrated Deadline into Sample Workflow.

Replace meta model references with UML diagrams.

Add section describing how to specify web services in xpdl.

Version 0.09 – Editor: Roberta Norin (robertan@attbi.com)

Added Chapter 8 – Sample Workflow.

Version 0.08 – Editor: Roberta Norin (robertan@attbi.com) Contributor: Mike Gilger (Identitech)

Removed DataTypes from WorkflowProcess.

Added BOOLEAN and PERFORMER to BasicType.

Removed PlainType Element from Schema.

Removed reference to PlainType from DataTypes

Added Script Element.

Add reference to Script Element to Package.

Removed left over references to LOOP in Conformance class and transition discussions.

Completed Condition table in Section 7.6.1.

Added discussion of loops to Section 7.6.

Version 0.07 – Editor: Roberta Norin (robertan@attbi.com)

Reconfigured the DataTypes element (which was not being used) to be an xsd:group that contained references to all the data types; refer to this group wherever the list of data types was repeated.

Edited the Data Types Section to emphasize the use of SchemaType to define complex data, to clarify the use of TypeDeclarations, and to take advantage of the DataTypes group simplification.

Moved SchemaType discussion to be under Complex Data types.

Version 0.06 – Editor: Roberta Norin (robertan@attbi.com)

Added AccessLevel attribute to WorkflowProcess

Added ExternalReference to Participant

Removed Loop Implementation from WorkflowActivity/Implementation

Removed Loop Element.

Removed Loop Attribute from Transition.

Removed Loop Activity from Figure 7.1.

Added TargetNamespace designation to schema (.xsd). Used xpdl namespace prefix in references to xpdl elements.

Added SchemaType and ExternalReference to all lists of Data Types.

Rearranged all lists of Data Types so that the old way of declaring complex types (array, record, etc.) are last in list of choices.

Version 0.05 – Editor: Roberta Norin (robertan@attbi.com)

Removed (redundant) discussion of Parameters under WorkflowProcess Activity and folded it into Formal Parameters section 7.1.2.

Completed missing text in tables in Chapter 7.

Version 0.04 – Editors: Mike Marin (mmarin@filenet.com ) and Roberta Norin (rnorin@apengines.com)

Incorporates modifications discussed in the May WfMC meeting.

This version uses a XML Schema instead of a DTD to describe XPDL

Added External References, which provides a way to interact with web services (WSDL) and other external definitions.

Added Schema Type, that allows for the definition of complex types by using a XML schema.

Introduced the concept of exception for routing.

Versions 0.02/0.03 – Editor: Mike Marin (mmarin@filenet.com)

Changes based on review by working group 1 during the New York meeting May 3 and 4 of 2001. This version has significant input from Roberta Norin (AP Engines), Robert Shapiro (Cape Visions), and all the other participants of the working group during the New York meeting.

Version 0.01 – Editor: Mike Marin (mmarin@filenet.com)

Initial Version.

The intended audience for this document is primarily vendor organizations who seek to implement the XML Process Definition Language (XPDL) of the Workflow Management Coalition (WfMC). It may also be of interest to those seeking to assess conformance claims made by vendors for their products. Comments should be addressed to the Workflow Management Coalition.

The WfMC has identified five functional interfaces to a workflow service as part of its standardization program. This specification forms part of the documentation relating to “Interface one” - supporting Process Definition Import and Export. This interface includes a common meta-model for describing the process definition (this specification) and also an XML schema for the interchange of process definitions.

A variety of different tools may be used to analyse, model, describe and document a business process. The workflow process definition interface defines a common interchange format, which supports the transfer of workflow process definitions between separate products. The interface also defines a formal separation between the development and run-time environments, enabling a process definition, generated by one modelling tool, to be used as input to a number of different workflow run-time products. A workflow process definition, generated by a build-time tool, is capable of interpretation in different workflow runtime products. Process definitions transferred between these products or stored in a separate repository are accessible via that common interchange format. To provide a common method to access and describe workflow definitions, a workflow process definition meta-data model has been established. This meta-data model identifies commonly used entities within a process definition. A variety of attributes describe the characteristics of this limited set of entities. Based on this model, vendor specific tools can transfer models via a common exchange format.

One of the key elements of the XPDL is its extensibility to handle information used by a variety of different tools. XPDL may never be capable of supporting all additional information requirements in all tools. Based upon a limited number of entities that describe a workflow process definition (the "Minimum Meta Model"), the XPDL supports a number of differing approaches. One of the most important elements of XPDL is a generic construct that supports vendor specific attributes for use within the common representation. We recommend that any missing attributes be proposed to the WfMC interface one workgroup for inclusion in future releases.

This document describes the meta-model, which is used to define the objects and attributes contained within a process definition. The XPDL grammar is directly related to these objects and attributes. This approach needs two operations to be provided by a vendor:

Import a workflow definition from XPDL.

Export a workflow definition from the vendor's internal representation to XPDL.

A vendor can use a XSL style sheet to comply with those two operations. All keywords and terms used within this specification are based upon the WfMC Glossary. For the purpose of this document, the terms process definition, business process model, and workflow model are all considered to represent the same concept, and therefore, they are used interchangeably.

4.1. Conformance

A vendor can not claim conformance to this or any other WfMC specification unless specifically authorised to make that claim by the WfMC. WfMC grants this permission only upon the verification of the particular vendor’s implementation of the published specification, according to applicable test procedures defined by WfMC. Conformance for process definition import / export is essentially based upon conformance to the XPDL grammar. However, there is a mandatory minimum set of objects, as specified within this document, which must be supported within XPDL. But, given the wide variation of capabilities in modelling tools, it is reasonable to assume that an individual tool might conform to this specification but not be able to swap complete definitions with all other conforming products. A product that claims conformance must generate valid, syntactically correct XPDL, and must be able to read all valid XPDL.

The following documents are associated with this document and should be used as a reference. General background information:

WfMC Terminology & Glossary (WfMC-TC-1011)

WfMC Reference Model (WfMC-TC-1003)

WfMC API specifications, which include process definition manipulation APIs:

WfMC Client Application API Specifications (WAPI) (WfMC-TC-1009)

WfMC Process Definition Interchange – Process Model (WfMC-TC-1016-P)

Workflow process interoperability, used to support process invocation on a remote workflow service:

Workflow Interoperability - Abstract Specifications (WfMC-TC-1012)

Interoperability - Internet E-mail MIME Binding (WfMC-TC-1018)

Accompanying documents:

The Resource Model (Organizational Model: WfMC TC-1016-O)

A Process Definition is defined as:

The representation of a business process in a form that supports automated manipulation, such as modeling, or enactment by a workflow management system. The process definition consists of a network of activities and their relationships, criteria to indicate the start and termination of the process, and information about the individual activities, such as participants, associated IT applications and data, etc. (WfMC Glossary - WfMCTC-1011)

The process definition provides an environment for a rich description of a process that can be used for the following,

Act as a template for the creation and control of instances of that process during process enactment.

For simulation and forecasting.

As a basis to monitor and analyse enacted processes.

For documentation, visualization, and knowledge management.

The process definition may contain references to subflow, separately defined, which make up part of the overall process definition. An initial process definition will contain at least the minimal set of objects and attributes necessary to initiate and support process execution. Some of these objects and attributes will be inherited by each created instance of the process. The WfMC Glossary also contains descriptions of, and common terminology for, the basic concepts embodied within a process definition such as activities, transitions, workflow relevant data and participants, etc.

5.1. Approaches to Process Definition Interchange

This specification uses XML as the mechanism for process definition interchange. XPDL forms a common interchange standard that enables products to continue to support arbitrary internal representations of process definitions with an import/export function to map to/from the standard at the product boundary. A variety of different mechanisms may be used to transfer process definition data between systems according to the characteristics of the various business scenarios. In all cases the process definition must be expressed in a consistent form, which is derived from the common set of objects, relationships and attributes expressing its underlying concepts. The principles of process definition interchange are illustrated in Figure 5-1: The Concept of the Process Definition Interchange.

The Meta-Model describes the top -level entities contained within a Process Definition, their relationships and attributes (including some which may be defined for simulation or monitoring purposes rather than for enactment). It also defines various conventions for grouping process definitions into related process models and the use of common definition data across a number of different process definitions or models.The top-level entities are shown in the following figure:

For each of the above entities, there is an associated set of properties, which describe the characteristics of the entity. The following sections describe these entities and properties in more detail.

6.1. Entities Overview

The meta-model identifies the basic set of entities used in the exchange of process definitions. The top -level entities are as follows:

The Process Definition entity provides contextual information that applies to other entities within the process. It is a container for the process itself and provides information associated with administration (creation date, author, etc.) or to be used during process execution (initiation parameters to be used, execution priority, time limits to be checked, person to be notified, simulation information, etc.).

A process definition consists of one or more activities, each comprising a logical, self-contained unit of work within the process. An activity represents work, which will be processed by a combination of resource (specified by participant assignment) and/or computer applications (specified by application assignment). Other optional information may be associated with the activity such as an information on whether it is to be started / finished automatically by the workflow management system or its priority relative to other activities where contention for resource or system services occurs. Usage of specific workflow relevant data items by the activity may also be specified. The scope of an activity is local to a specific process definition (although see the description of a subflow activity below). An activity may be a subflow - in this case it is a container for the execution of a (separately specified) process definition, which may be executed locally within the same workflow service, or (possibly using the process interoperability interface) on a remote service. The process definition identified within the subflow contains its own definition of activities, internal transitions, resource, and application assignments (although these may be inherited from a common source). In- and out-parameters permit the exchange of any necessary workflow relevant data between calling and called process (and, where necessary, on return).

An activity may be a block activity that executes an activity set, or map of activities and transitions. Activit ies and transitions within an activity set share the name space of the containing process. Finally, a dummy activity is a skeletal activity, which performs no work processing (and therefore has no associated resource or applications), but simply supports routing decisions among the incoming transitions and/or among the outgoing transitions.

6.1.3. Transition Information

Activities are related to one another via flow control conditions (transition information). Each individual transition has three elementary properties, the from-activity, the to-activity and the condition under which the transition is made. Transition from one activity to another may be conditional (involving expressions which are evaluated to permit or inhibit the transition) or unconditional. The transitions within a process may result in the sequential or parallel peration of individual activities within the process.

The information related to associated split or join conditions is defined within the appropriate activity, split as a form of “post activity” processing in the from-activity, join as a form of “pre-activity” processing in the to- activity. This approach allows the workflow control processing associated with process instance thread splitting and synchronization to be managed as part of the associated activity, and retains transitions as simple route assignment functions. The scope of a particular transition is local to the process definition, which contains it and the associated activities.

More complex transitions, which cannot be expressed using the simple elementary transition and the split and join functions associated with the from- and to- activities, are formed using dummy activities, which can be specified as intermediate steps between real activities allowing additional combinations of split and/or join operations. Using the basic transition entity plus dummy activities, routing structures of arbitrary complexity can be specified. Since several different approaches to transition control exist within t he industry, several conformance classes are specified within XPDL. These are described later in the document.

This provides descriptions of resources that can act as the performer of the various activities in the process definition. The particular resources, which can be assigned to perform a specific activity, are specified as an attribute of the activity, participant assignment, which links the activity to the set of resources (within the workflow participant declaration) which may be allocated to it. The workflow participant declaration does not necessarily refer to a human or a single person, but may also identify a set of people of appropriate skill or responsibility, or machine automata resource rather than human. The meta-model includes some simple types of resource that may be defined within the workflow participant declaration.

The resource repository accounts for the fact that participants can be humans, programs, or machines. In more sophisticated scenarios the participant declaration may refer to a resource repository, which may be an Organizational Model in the case of human participants. Note that this specification does not define or require a resource repository.

This provides descriptions of the IT applications or interfaces which may be invoked by the workflow service to support, or wholly automate, the processing associated with each activity, and identified within the activity by an application assignm ent attribute (or attributes). Such applications may be generic industry tools, specific departmental or enterprise services, or localized procedures implemented within the framework of the workflow management system. The workflow application definition reflects the interface between the workflow engine and the application or interface, including any parameters to be passed.

This defines the data that is created and used within each process instance during process execution. The data is made available to activities or applications executed during the workflow and may be used to pass persistent information or intermediate results between activities and/or for evaluation in conditional expressions such as in transitions or participant assignment. Workflow relevant data is of particular type. XPDL includes definition of various basic and complex data types, (including date, string, etc.) Activities, invoked applications and/or transition conditions may refer to workflow process relevant data.

This is data which is maintained by the workflow management system or the local system environment, but which may be accessed by workflow activities or used by the workflow management system in the evaluation of conditional expressions in the same way as workflow relevant data.

The meta-model (and associated XPDL) assumes a number of standard data types (string, reference, integer, float, date/time, etc.); such data types are relevant to workflow relevant data, system or environmental data or participant data. Expressions may be formed using such data types to support conditional evaluations. Data types may be extended using an XML schema or a reference to data defined in an external source.

As indicated in the diagram above, the process model includes various entities whose scope may be wider than a single process definition. In particular the definitions of participants, applications and workflow relevant data may be referenced from a number of process definitions. The meta-model assumes the use of a common process definition repository, associated with the workflow management system, to hold the various entity types comprising the process definition. Within the repository itself and to support the efficient transfer of process definition data to/from the repository, the concept of a package is introduced, which acts as a container for the grouping of common data entities from a number of different process definitions, to avoid redefinition within each individual process definition. The package provides a container to hold a number of common attributes from the workflow process definition entity (author, version, status, etc.). Each process definition contained within the package will automatically inherit any common attributes from the package, unless they are separately re-specified locally within the process definition Within a package, the scope of the definitions of some entities is global and these entities can be referenced from all workflow process definitions (and associated activities and transitions) contained within the package. Those entities are:

Workflow participant specification

Workflow application declaration, and

Workflow relevant data

The package reference allows the use within the package or its contained objects of references to top-level entities in the referenced external package:

Process ids for subflow reference

Workflow participant specifications

Workflow application declarations

Conventions on name and identifier management across different packages within the same repository address space to achieve any necessary global uniqueness are for user/vendor definition. The assumed convention during process enactment is that name reference searches follow the sequence:

Process ids - firstly within the same model (including any references to process definitions for remote execution on a different service), then within any externally referenced model

Applications / participants - firstly within the same model, then within any externally referenced model Workflow relevant data naming must be unique within a package; where such data is passed between processes as parameters the convention at this version of specification is that copy semantics will be used. R esponsibility rests with process designers / administrators to ensure consistent name / data type usage within process definitions / models to support subflow operations (including any required remote process interoperability).

The met a-model identifies the basic set of entities and attributes for the exchange of process definitions. For a Process Definition the following entities must be defined, either explicitly at the level of the process definition, or by inheritance directly or via cross reference from a surrounding package:

Workflow Process Activity

Transition Information

Workflow Participant Specification

Workflow Application Declaration

Workflow Relevant Data

These entities contain attributes that support a common description mechanism for processes. They are described in the subsequent document sections.

— XML Process Definition Language

Version 1.0 – Editor: Roberta Norin (robertan@attbi.com).

Added processContent=”lax” attribute to specification of SchemaType, ExtendedAttribute, and Xpression.

Changed URI references in the sample workflow to point to documents on the wfmc.org web site.

Changed SubFlow Id’s in sample workflow to refer to Workflow Process by Id rather than Name.

Version 0.10 -- Editor: Roberta Norin (robertan@attbi.com ). Contributors: Seth Osher (Intuitive Products International Corp.) and Robert Shapiro (Cape Visions).

Removed InlineBlock and BlockName elements from schema, from content of ransitionRestriction. Removed BlockName element, and from specification.

Added ActivitySets and BlockActivity to schema and to specification

Removed maxOccurs attribute from Activities in schema.

Added Deadline element to schema and specification.

Integrated Deadline into Sample Workflow.

Replace meta model references with UML diagrams.

Add section describing how to specify web services in xpdl.

Version 0.09 – Editor: Roberta Norin (robertan@attbi.com)

Added Chapter 8 – Sample Workflow.

Version 0.08 – Editor: Roberta Norin (robertan@attbi.com) Contributor: Mike Gilger (Identitech)

Removed DataTypes from WorkflowProcess.

Added BOOLEAN and PERFORMER to BasicType.

Removed PlainType Element from Schema.

Removed reference to PlainType from DataTypes

Added Script Element.

Add reference to Script Element to Package.

Removed left over references to LOOP in Conformance class and transition discussions.

Completed Condition table in Section 7.6.1.

Added discussion of loops to Section 7.6.

Version 0.07 – Editor: Roberta Norin (robertan@attbi.com)

Reconfigured the DataTypes element (which was not being used) to be an xsd:group that contained references to all the data types; refer to this group wherever the list of data types was repeated.

Edited the Data Types Section to emphasize the use of SchemaType to define complex data, to clarify the use of TypeDeclarations, and to take advantage of the DataTypes group simplification.

Moved SchemaType discussion to be under Complex Data types.

Version 0.06 – Editor: Roberta Norin (robertan@attbi.com)

Added AccessLevel attribute to WorkflowProcess

Added ExternalReference to Participant

Removed Loop Implementation from WorkflowActivity/Implementation

Removed Loop Element.

Removed Loop Attribute from Transition.

Removed Loop Activity from Figure 7.1.

Added TargetNamespace designation to schema (.xsd). Used xpdl namespace prefix in references to xpdl elements.

Added SchemaType and ExternalReference to all lists of Data Types.

Rearranged all lists of Data Types so that the old way of declaring complex types (array, record, etc.) are last in list of choices.

Version 0.05 – Editor: Roberta Norin (robertan@attbi.com)

Removed (redundant) discussion of Parameters under WorkflowProcess Activity and folded it into Formal Parameters section 7.1.2.

Completed missing text in tables in Chapter 7.

Version 0.04 – Editors: Mike Marin (mmarin@filenet.com ) and Roberta Norin (rnorin@apengines.com)

Incorporates modifications discussed in the May WfMC meeting.

This version uses a XML Schema instead of a DTD to describe XPDL

Added External References, which provides a way to interact with web services (WSDL) and other external definitions.

Added Schema Type, that allows for the definition of complex types by using a XML schema.

Introduced the concept of exception for routing.

Versions 0.02/0.03 – Editor: Mike Marin (mmarin@filenet.com)

Changes based on review by working group 1 during the New York meeting May 3 and 4 of 2001. This version has significant input from Roberta Norin (AP Engines), Robert Shapiro (Cape Visions), and all the other participants of the working group during the New York meeting.

Version 0.01 – Editor: Mike Marin (mmarin@filenet.com)

Initial Version.

The intended audience for this document is primarily vendor organizations who seek to implement the XML Process Definition Language (XPDL) of the Workflow Management Coalition (WfMC). It may also be of interest to those seeking to assess conformance claims made by vendors for their products. Comments should be addressed to the Workflow Management Coalition.

The WfMC has identified five functional interfaces to a workflow service as part of its standardization program. This specification forms part of the documentation relating to “Interface one” - supporting Process Definition Import and Export. This interface includes a common meta-model for describing the process definition (this specification) and also an XML schema for the interchange of process definitions.

A variety of different tools may be used to analyse, model, describe and document a business process. The workflow process definition interface defines a common interchange format, which supports the transfer of workflow process definitions between separate products. The interface also defines a formal separation between the development and run-time environments, enabling a process definition, generated by one modelling tool, to be used as input to a number of different workflow run-time products. A workflow process definition, generated by a build-time tool, is capable of interpretation in different workflow runtime products. Process definitions transferred between these products or stored in a separate repository are accessible via that common interchange format. To provide a common method to access and describe workflow definitions, a workflow process definition meta-data model has been established. This meta-data model identifies commonly used entities within a process definition. A variety of attributes describe the characteristics of this limited set of entities. Based on this model, vendor specific tools can transfer models via a common exchange format.

One of the key elements of the XPDL is its extensibility to handle information used by a variety of different tools. XPDL may never be capable of supporting all additional information requirements in all tools. Based upon a limited number of entities that describe a workflow process definition (the "Minimum Meta Model"), the XPDL supports a number of differing approaches. One of the most important elements of XPDL is a generic construct that supports vendor specific attributes for use within the common representation. We recommend that any missing attributes be proposed to the WfMC interface one workgroup for inclusion in future releases.

This document describes the meta-model, which is used to define the objects and attributes contained within a process definition. The XPDL grammar is directly related to these objects and attributes. This approach needs two operations to be provided by a vendor:

Import a workflow definition from XPDL.

Export a workflow definition from the vendor's internal representation to XPDL.

A vendor can use a XSL style sheet to comply with those two operations. All keywords and terms used within this specification are based upon the WfMC Glossary. For the purpose of this document, the terms process definition, business process model, and workflow model are all considered to represent the same concept, and therefore, they are used interchangeably.

4.1. Conformance

A vendor can not claim conformance to this or any other WfMC specification unless specifically authorised to make that claim by the WfMC. WfMC grants this permission only upon the verification of the particular vendor’s implementation of the published specification, according to applicable test procedures defined by WfMC. Conformance for process definition import / export is essentially based upon conformance to the XPDL grammar. However, there is a mandatory minimum set of objects, as specified within this document, which must be supported within XPDL. But, given the wide variation of capabilities in modelling tools, it is reasonable to assume that an individual tool might conform to this specification but not be able to swap complete definitions with all other conforming products. A product that claims conformance must generate valid, syntactically correct XPDL, and must be able to read all valid XPDL.

The following documents are associated with this document and should be used as a reference. General background information:

WfMC Terminology & Glossary (WfMC-TC-1011)

WfMC Reference Model (WfMC-TC-1003)

WfMC API specifications, which include process definition manipulation APIs:

WfMC Client Application API Specifications (WAPI) (WfMC-TC-1009)

WfMC Process Definition Interchange – Process Model (WfMC-TC-1016-P)

Workflow process interoperability, used to support process invocation on a remote workflow service:

Workflow Interoperability - Abstract Specifications (WfMC-TC-1012)

Interoperability - Internet E-mail MIME Binding (WfMC-TC-1018)

Accompanying documents:

The Resource Model (Organizational Model: WfMC TC-1016-O)

A Process Definition is defined as:

The representation of a business process in a form that supports automated manipulation, such as modeling, or enactment by a workflow management system. The process definition consists of a network of activities and their relationships, criteria to indicate the start and termination of the process, and information about the individual activities, such as participants, associated IT applications and data, etc. (WfMC Glossary - WfMCTC-1011)

The process definition provides an environment for a rich description of a process that can be used for the following,

Act as a template for the creation and control of instances of that process during process enactment.

For simulation and forecasting.

As a basis to monitor and analyse enacted processes.

For documentation, visualization, and knowledge management.

The process definition may contain references to subflow, separately defined, which make up part of the overall process definition. An initial process definition will contain at least the minimal set of objects and attributes necessary to initiate and support process execution. Some of these objects and attributes will be inherited by each created instance of the process. The WfMC Glossary also contains descriptions of, and common terminology for, the basic concepts embodied within a process definition such as activities, transitions, workflow relevant data and participants, etc.

5.1. Approaches to Process Definition Interchange

This specification uses XML as the mechanism for process definition interchange. XPDL forms a common interchange standard that enables products to continue to support arbitrary internal representations of process definitions with an import/export function to map to/from the standard at the product boundary. A variety of different mechanisms may be used to transfer process definition data between systems according to the characteristics of the various business scenarios. In all cases the process definition must be expressed in a consistent form, which is derived from the common set of objects, relationships and attributes expressing its underlying concepts. The principles of process definition interchange are illustrated in Figure 5-1: The Concept of the Process Definition Interchange.

The Meta-Model describes the top -level entities contained within a Process Definition, their relationships and attributes (including some which may be defined for simulation or monitoring purposes rather than for enactment). It also defines various conventions for grouping process definitions into related process models and the use of common definition data across a number of different process definitions or models.The top-level entities are shown in the following figure:

For each of the above entities, there is an associated set of properties, which describe the characteristics of the entity. The following sections describe these entities and properties in more detail.

6.1. Entities Overview

The meta-model identifies the basic set of entities used in the exchange of process definitions. The top -level entities are as follows:

The Process Definition entity provides contextual information that applies to other entities within the process. It is a container for the process itself and provides information associated with administration (creation date, author, etc.) or to be used during process execution (initiation parameters to be used, execution priority, time limits to be checked, person to be notified, simulation information, etc.).

A process definition consists of one or more activities, each comprising a logical, self-contained unit of work within the process. An activity represents work, which will be processed by a combination of resource (specified by participant assignment) and/or computer applications (specified by application assignment). Other optional information may be associated with the activity such as an information on whether it is to be started / finished automatically by the workflow management system or its priority relative to other activities where contention for resource or system services occurs. Usage of specific workflow relevant data items by the activity may also be specified. The scope of an activity is local to a specific process definition (although see the description of a subflow activity below). An activity may be a subflow - in this case it is a container for the execution of a (separately specified) process definition, which may be executed locally within the same workflow service, or (possibly using the process interoperability interface) on a remote service. The process definition identified within the subflow contains its own definition of activities, internal transitions, resource, and application assignments (although these may be inherited from a common source). In- and out-parameters permit the exchange of any necessary workflow relevant data between calling and called process (and, where necessary, on return).

An activity may be a block activity that executes an activity set, or map of activities and transitions. Activit ies and transitions within an activity set share the name space of the containing process. Finally, a dummy activity is a skeletal activity, which performs no work processing (and therefore has no associated resource or applications), but simply supports routing decisions among the incoming transitions and/or among the outgoing transitions.

6.1.3. Transition Information

Activities are related to one another via flow control conditions (transition information). Each individual transition has three elementary properties, the from-activity, the to-activity and the condition under which the transition is made. Transition from one activity to another may be conditional (involving expressions which are evaluated to permit or inhibit the transition) or unconditional. The transitions within a process may result in the sequential or parallel peration of individual activities within the process.

The information related to associated split or join conditions is defined within the appropriate activity, split as a form of “post activity” processing in the from-activity, join as a form of “pre-activity” processing in the to- activity. This approach allows the workflow control processing associated with process instance thread splitting and synchronization to be managed as part of the associated activity, and retains transitions as simple route assignment functions. The scope of a particular transition is local to the process definition, which contains it and the associated activities.

More complex transitions, which cannot be expressed using the simple elementary transition and the split and join functions associated with the from- and to- activities, are formed using dummy activities, which can be specified as intermediate steps between real activities allowing additional combinations of split and/or join operations. Using the basic transition entity plus dummy activities, routing structures of arbitrary complexity can be specified. Since several different approaches to transition control exist within t he industry, several conformance classes are specified within XPDL. These are described later in the document.

This provides descriptions of resources that can act as the performer of the various activities in the process definition. The particular resources, which can be assigned to perform a specific activity, are specified as an attribute of the activity, participant assignment, which links the activity to the set of resources (within the workflow participant declaration) which may be allocated to it. The workflow participant declaration does not necessarily refer to a human or a single person, but may also identify a set of people of appropriate skill or responsibility, or machine automata resource rather than human. The meta-model includes some simple types of resource that may be defined within the workflow participant declaration.

The resource repository accounts for the fact that participants can be humans, programs, or machines. In more sophisticated scenarios the participant declaration may refer to a resource repository, which may be an Organizational Model in the case of human participants. Note that this specification does not define or require a resource repository.

This provides descriptions of the IT applications or interfaces which may be invoked by the workflow service to support, or wholly automate, the processing associated with each activity, and identified within the activity by an application assignm ent attribute (or attributes). Such applications may be generic industry tools, specific departmental or enterprise services, or localized procedures implemented within the framework of the workflow management system. The workflow application definition reflects the interface between the workflow engine and the application or interface, including any parameters to be passed.

This defines the data that is created and used within each process instance during process execution. The data is made available to activities or applications executed during the workflow and may be used to pass persistent information or intermediate results between activities and/or for evaluation in conditional expressions such as in transitions or participant assignment. Workflow relevant data is of particular type. XPDL includes definition of various basic and complex data types, (including date, string, etc.) Activities, invoked applications and/or transition conditions may refer to workflow process relevant data.

This is data which is maintained by the workflow management system or the local system environment, but which may be accessed by workflow activities or used by the workflow management system in the evaluation of conditional expressions in the same way as workflow relevant data.

The meta-model (and associated XPDL) assumes a number of standard data types (string, reference, integer, float, date/time, etc.); such data types are relevant to workflow relevant data, system or environmental data or participant data. Expressions may be formed using such data types to support conditional evaluations. Data types may be extended using an XML schema or a reference to data defined in an external source.

As indicated in the diagram above, the process model includes various entities whose scope may be wider than a single process definition. In particular the definitions of participants, applications and workflow relevant data may be referenced from a number of process definitions. The meta-model assumes the use of a common process definition repository, associated with the workflow management system, to hold the various entity types comprising the process definition. Within the repository itself and to support the efficient transfer of process definition data to/from the repository, the concept of a package is introduced, which acts as a container for the grouping of common data entities from a number of different process definitions, to avoid redefinition within each individual process definition. The package provides a container to hold a number of common attributes from the workflow process definition entity (author, version, status, etc.). Each process definition contained within the package will automatically inherit any common attributes from the package, unless they are separately re-specified locally within the process definition Within a package, the scope of the definitions of some entities is global and these entities can be referenced from all workflow process definitions (and associated activities and transitions) contained within the package. Those entities are:

Workflow participant specification

Workflow application declaration, and

Workflow relevant data

The package reference allows the use within the package or its contained objects of references to top-level entities in the referenced external package:

Process ids for subflow reference

Workflow participant specifications

Workflow application declarations

Conventions on name and identifier management across different packages within the same repository address space to achieve any necessary global uniqueness are for user/vendor definition. The assumed convention during process enactment is that name reference searches follow the sequence:

Process ids - firstly within the same model (including any references to process definitions for remote execution on a different service), then within any externally referenced model

Applications / participants - firstly within the same model, then within any externally referenced model Workflow relevant data naming must be unique within a package; where such data is passed between processes as parameters the convention at this version of specification is that copy semantics will be used. R esponsibility rests with process designers / administrators to ensure consistent name / data type usage within process definitions / models to support subflow operations (including any required remote process interoperability).

The met a-model identifies the basic set of entities and attributes for the exchange of process definitions. For a Process Definition the following entities must be defined, either explicitly at the level of the process definition, or by inheritance directly or via cross reference from a surrounding package:

Workflow Process Activity

Transition Information

Workflow Participant Specification

Workflow Application Declaration

Workflow Relevant Data

These entities contain attributes that support a common description mechanism for processes. They are described in the subsequent document sections.