Chapter 5. Variables

Global variables exist in a knowledge session and can be accessed and are shared by all assets in that session. They belong to the particular session of the Knowledge Base and they are used to pass information to the engine. Every global variable defines its ID and item subject reference. The ID serves as the variable name and must be unique within the process definition. The item subject reference defines the data type the variable stores.

Global variables are initialized either when the process with the variable definition is added to the session or when the session is initialized with globals as its parameters.

Values of global variables can typically be changed during the assignment, which is a mapping between a process variable and an activity variable. The global variable is then associated with the local activity context, local activity variable, or by a direct call to the variable from a child 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 completion.

A process variable is a variable that exists in a process context and can be accessed by its process or its child elements. Process variables belong to a particular process instance and cannot be accessed by other process instances. Every process variable defines its ID and item subject reference: the ID serves as the variable name and must be unique within the process definition. The item subject reference defines the data type the variable stores.

Process variables are initialized when the process instance is created. Their value can be changed by the process activities using the Assignment, when the global variable is associated with the local Activity context, local Activity variable, or by a direct call to the variable from a child context.

Note that process variables should be mapped to local variables.

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 has 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. This enables you to maintain relative independence of the parent element that accommodates the local variable. Such isolation might help prevent technical exceptions.

A local variable is a variable that exists in a child element context of a process and can be accessed only from within this context. Local variables belong to the particular element of a process.

For tasks, with the exception of the Script task, you can define Data Input Assignments and Data Output Assignments in the Assignments property. Data Input Assignment defines variables that enter the Task and therefore provide the entry data needed for the task execution. The Data Output Assignments can refer to the context of the Task after execution to acquire output data.

User Tasks present data related to the actor that is executing the User Task. Additionally, User Tasks also request the actor to provide result data related to the execution.

To request and provide the data, use task forms and map the data in the Data Input Assignment parameter to a variable. Map the data provided by the user in the Data Output Assignment parameter if you want to preserve the data as output.