• Workflow - A protocol that describes an experimental process written in a computer-parsable scripting language. Covers both workflow templates and workflow instance.
• Workflow template - A protocol that describes an experimental process without detailing the particular services, inputs or configuration of an experiment.
• Workflow instance – A fully resolved workflow template that is being or has been run by a workflow enactor.
• Workflow enactor – A service which can execute a resolved workflow template by calling individual services in the specified order and transferring data between those services.
• Workflow resolution – The process of substituting classes of service denoted for individual steps in the workflow with particular services instance at a specific web/ grid location.
• Service class – A group of Grid or Web Services with an explicit definition of the criteria for membership of that group. The group does not necessarily always have functioning member services. Within the context of experimental design we focus on membership criteria describing functionality. A Grid service factory can instantiate grid services of a very concrete and narrowly defined class (i.e. all instances will be identical in all respects other than location).
• Service instance – A Grid or web service.
• Service resolution – Replacing a class of service with a service instance that is a valid member of that class.
• Service instantiation – In the grid context it is possible to instantiate a new service to perform a workflow step given a description of the class and access to the corresponding grid service factory.
• Service substitution – Replacing one service instance with another functionally equivalent instance.
• Workflow harmonisation – Modifying the low level design of a workflow to accommodate (a) substitution of a functionally equivalent service instance that differs in its low level interface, or (b) resolution of a service class (which does not commit to a low level interface) with a service instance that has particular interface requirements.

-- ChrisWroe - 19 Sep 2003