__see also [Workflow Description Languages]__ 1.1 Our definition The Workflow Management Coalition [WfMC] defines __workflow__ as "The automation of a business process, in whole or part, during which documents, information or tasks are passed from one participant to another for action, according to a set of procedural rules". In the context of Grid computing the term workflow usually concerns the automation of distributed IT processes. In [K-Wf Grid] the workflow model is based on [Petri net]s. A Petri net consists of two basic elements: __transitions__ (rectangle) and __places__ (circle). Transitions and places are connected with each other by directed __edges__ (arcs). Transitions are related to activities, whereas places store the state of the workflow by means of __tokens__. __Workflow constructs__ are certain sub-regions of the workflow that can be used as common control structures, such as sequence, choice, split/join, and iteration. Not every sub-region of a workflow may constitute a reasonable workflow construct. In K-Wf Grid every __activity__ (synonyms: __task, job__) has a specific level of abstraction ranging from abstract to concrete. An abstract activity contains a very brief description of the task and cannot be executed automatically in the real world without further refinement, whereas a concrete activity is mapped to a specific instance of a Web Service operation. Only concrete activities can be directly executed automatically in the real world. Within a Web service operation, external applications (e.g. flood forecasting simulation) written in C/C++/Fortran may be invoked. An execution of an activity is called an activity instance. The Web service operations invoked in activity instances are called invoked applications of activities. An invoked application can be considered as a set of code regions. A code region is a sequence of program statements. Code regions can be entire program units (functions or subroutines), loops (do while, for), function calls. 1.1 Definition by the [OGSA]-WG glossary __Workflow__ is a pattern of business process interaction, not necessarily corresponding to a fixed set of business processes. All such interactions may be between services residing within a single data center or across a range of different platforms and implementations anywhere. __Choreography__ describes required patterns of interaction among services and templates for sequences (or more structures) of interactions. __Orchestration__ describes the ways in which business processes are constructed from Web services and other business processes, and how these processes interact. 1.1 TWiki MyGrid - http://twiki.mygrid.org.uk/twiki/bin/view/Mygrid/WorkflowDefinitions 2005-05-31 15:41:10.932 2004-09-21 09:44:13.309