Data is maintained and passed around in the workflow engine as workflow data objects and list workflow data objects. These are logical objects defined in the process definition that have a name and a list of attributes of various types to which data can be assigned. They are conceptually similar to objects in programming languages although their manifestation in the workflow system is of course quite different. Workflow data object values may be written at process enactment or from the output of various activity types.
Workflow data object instances and list workflow data object instances exist as soon as the process is enacted and exist until the process completes. As such they are available to be used in the activities and the transitions throughout the lifetime of that process instance. It is therefore the responsibility of the process designer to ensure that attributes of workflow data objects are populated before they are used. Attempts to use workflow data object attributes before they are populated will result in failures at runtime.