11.7. Variables

Variables are elements that serve for storing a particular type of data during runtime. The type of data a variable contains is defined by its data type.
Just like any context data, every variable has its scope that defines its "visibility". An element, such as a Process, Sub-Process, or Task can only access variables in its own and parent contexts: variables defined in the element's child elements cannot be accessed. Therefore, when an elements requires access to a variable on runtime, its own context is searched first. If the variable cannot be found directly in the element's context, the immediate parent context is searched. The search continues to "level up" until the Process context is reached; in case of Globals, the search is performed directly on the Session container. If the variable cannot be found, a read access request returns null and a write access produces an error message, and the Process continues its execution. Variables are searched for based on their ID.
In Red Hat JBoss BPM Suite, variables can live in the following contexts:
  • Session context: Globals are visible to all Process instances and assets in the given Session and are intended to be used primarily by business rules and by constrains. The are created dynamically by the rules or constrains.
  • Process context: Process variables are defined as properties in the BPMN2 definition file and are visible within the Process instance. They are initialized at Process creation and destroyed on Process finish.
  • Element context: Local variables are available within their Process element, such as an Activity. They are initialized when the element context is initialized, that is, when the execution workflow enters the node and execution of the OnEntry action finished if applicable. They are destroyed when the element context is destroyed, that is, when the execution workflow leaves the element.
    Values of local variables can be mapped to Global or Process variables using the Assignment mechanism (refer to Section 11.8, “Assignment”). This allows you to maintain relative independence of the parent Element that accommodates the local variable. Such isolation may help prevent technical exceptions.