Table of Contents
This chapter describes how TWE works, corresponding to WfMC (Workflow Management Coalition) specifications (www.wfmc.org). WfMC provides an interface for workflow process definition. The interface defines a common meta-model for describing the process definition and XML schema for interchange of process definitions - XPDL (XML Process Definition Language). The focus is on XPDL schema elements, and TWE's property panels for editing them.
TWE is a tool for Process Definition modelling. The final output of this process modelling is a XPDL output file, which can be interpreted at runtime by the workflow engine(s). TWE accomplished three main goals:
Graphical representation of process definition
Export of process definitions to XPDL
Import of any valid XPDL and its graphical representation
TWE handles one (main) package at a time, although it displays in a read-only mode all the external packages of the main package (and all the external packages of external packages and so on). Main TWE component window is labeled Graph. It is the graphic representation of workflow process or activity set, depending on what is currently selected.
Participants are represented with swim lines which encapsulate other smaller blocks (don't be confused; participants can be horizontally or vertically oriented). Those blocks represent activities.
Lines which connect activities are transitions. Graph specific elements are Start and End bubbles. These elements are not the part of WfMC specification, although they appear in the resulting XPDL file as extended attribute elements.
The rest of XPDL elements can be accessed and modified through their panel properties.
The workflow process definition interface defines a common interchange format, which supports the transfer of workflow process definitions between different products. A workflow process definition, generated by TWE, is capable of interpretation in different workflow run-time products. The principles of Process Definition Interchange are based on Meta-Model framework. This meta-data model identifies commonly used entities within a process definition, their relationships and attributes. A variety of attributes describe the characteristics of this limited set of entities. Using this Meta-Model, TWE can transfer models using an XPDL as a common exchange format. Beside this interchange, TWE is also used for internal representation of process definitions. The whole concept is shown on the picture: | ![]() |
There is a mandatory minimum set of objects, which must be supported within XPDL. This "minimum meta-data model" identifies those commonly used entities within a process definition and describes their usage semantics. Extensibility is provided by the facility to encompass additional object attributes ("extended attributes") which can be included as extensions to the basic Meta-Model to meet the specific needs of an individual product or workflow system.
Corresponding to the previous picture with concept of Process Definition Interchange, this chapter gives overview of Meta-Model entities (Meta-Model framework) and explains representation of these objects in TWE (Internal representation) with XPDL attributes (XML representation) that are defined in it.
The meta-model identifies the basic set of entities and attributes for the exchange of process definitions.
For each of the above entities, there is an associated set of attributes (some mandatory and others optional) which describe the characteristics of the entity. If there is a need of using an additional characteristics, "extended attributes" for various entities may be defined to allow extension of the scope of the Meta-Model in a controlled manner.
All those entities except "Message Flow" and "Group" type artifacts are maintained by TWE. The current version of TWE is written as an XPDL 1 extension towards XPDL 2, and still does not support the whole XPDL 2 Meta-Model but only the parts necessary to support simple BPMN conformance, and still to allow workflow engines to execute XPDL 1 "migrated" process definitions.
"Resource Repository " is external to the workflow process definitions. In some complex processes, participant declaration may refer to a resource repository, which may be on Organisational Model (OM). WfMC Meta-Model specification defines a simple in-built (Minimal) Organisational Model or permits access to an externally defined OM. Note that XPDL specification does not define or require a resource repository.
TWE works only with a Minimal Organisational Model so there is no external Organisational Model provided. In this model, there aren't any relationships between participants. TWE may refer (import) any external XPDL structure - External Package. That External XPDL file may contain whole Organisational Model, so that External Package can act like Resource Repository.
As it is shown in the previous picture, minimal 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 Resource Repository. Repository holds 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. Each process definition contained within the package will automatically inherit any common attribute from the process model container, unless they are separately re-specified locally within the process definition.