Decision Task

Introduction

Decision Tasks are used to execute Business Rules encoded in DMN tables. You only have to indicate a Decision Table Reference; the mapping of the variable is configured in the Decision Table. See Decision Table Editor for details on creating a Decision Table.

Each input in the Decision Table is mapped to a variable which must be available in the process. The same is true for the output columns which do not necessarily have to exist.

Once the task is executed, the inputs are checked according to the Hit Policy defined in the table. If at least one rule matches, the values of the output columns are stored in the variables indicated in the table.

Example

In the following example, a Decision Task is used to determine the credit rating of a potential client.

Properties

General

Attribute	Type	Description	Category
Model Id	Text	Model Id identifies the element within the process model.	The model id, name and documentation properties can be found on any element. They are used respectively to uniquely identify the decision task, to give it a user-friendly name and to add a free-form description.
Name	Text	The name of the element. This is the name displayed in the diagram.
Documentation	Multiline Text	A free-form text that can be used to explain details about the particular element.
Decision table reference	Reference	Decision table reference to set for decision task.	Create or link a DMN decision table containing rules to this task. A decision table reference can be unlinked to allow another decision table to be linked in its place. Note that unlinking a decision table does not delete the form model itself. Alternatively a DMN decision service can be referenced instead of a decision table. These two references are exclusive (it's one of either).
In same deployment	Boolean	Set it to true if the referenced definition should be referenced from within the same app deployment. Set it to false to always use the newest definition.	The Same deployment flag is used to indicate that the DMN decision table that is used is part of the same app deployment package as where the current BPMN model is in. If unchecked, the latest version is used which can come from an app that is deployed at a later point in time. The Fallback to default tenant indicates that the deployed DMN decision table model will be taken from the default tenant if the model is not deployed in the tenant where the current process instance is running in. This is only relevant if Flowable is set up in multi-tenant mode.
Fallback to default tenant	Boolean	Indicates that the new instance will be created with the default tenant if it is not available on the current tenant. This is only relevant if the application runs multiple tenants.
Decision service reference	Reference	Decision service reference to set for decision task.	Create or link a DMN decision service containing multiple DMN decision tables to this task. A decision service reference can be unlinked to allow another decision service to be linked in its place. Note that unlinking a decision service does not delete the form model itself. Alternatively a DMN decision table can be referenced instead of a decision service. These two references are exclusive (it's one of either).
In same deployment for decision service	Boolean		The Same deployment flag is used to indicate that the DMN decision service that is used is part of the same app deployment package as where the current BPMN model is in. If unchecked, the latest version is used which can come from an app that is deployed at a later point in time. The Fallback to default tenant indicates that the deployed DMN decision service model will be taken from the default tenant if the model is not deployed in the tenant where the current process instance is running in. This is only relevant if Flowable is set up in multi-tenant mode.
Fallback to default tenant for decision service	Boolean

Multi Instance

Multi instance

Attribute	Type	Description	Category
Multi instance type	Selection: None Parallel Sequential	The type of multi-instance: default is 'None' meaning a single instance is created at runtime. Select either 'Parallel' or 'Sequential' if you want multiple instances to be created.	Multi-instance is used to define the repetition of this decision task at runtime. With multi-instance it is possible to have multiple evaluations of the DMN rules, either sequentially after each other or in parallel. For example, when referencing a collection one evaluation of the DMN rules is executed against each element of that collection.
Collection	Text	References a collection variable (for example a JSON array variable) by its name or using an expression that resolves to a collection.
Element variable	Text	The name of the variable where the currently processed element from the multi-instance collection configured above will be stored (for example, 'invoicePosition'). The element can then be accessed through an expression, e.g., ${invoicePosition}.
Element index variable	Text	The name of the variable where the index of the currently processed item from the multi-instance collection will be stored, for example, 'itemIndex'. The index is a number starting with 0 which is increased with every element that is being created. The index can then be accessed through an expression, e.g., ${itemIndex} further on in the process.
Cardinality	Text	A fixed number or an expression that resolved to an integer that controls the number of instances that will be created. This is typically used when there is no collection available or needed.
Completion condition	Text	An expression that should resolve to a boolean value. When evaluating to true, the remaining activity instances will be removed and the process instance will continue.

Variable aggregation

Attribute	Type	Description	Category
Variable Aggregations	List	Define an aggregation. Each element in this list will result in one aggregation variable.	When using multi-instance, there is often a need to create an aggregation of the variables created and/or updated in each instance. With variable aggregation, a JSON variable can be created that after all instances have been completed contains the summary of all the used variables. This is needed because for multi-instance, variables are persisted locally, to avoid clashes on the process instance level. Alternatively, an 'overview' variable can be created while the instances are still unfinished. Each aggregation consists of one or multiple definitions that map instance variables of one instance of the multi-instance to the aggregation variable.

Advanced

Attribute	Type	Description	Category
Optimize for only automatic steps	Boolean	(Advanced setting, only check it if you understand the implications) If checked, this instructs the Flowable engine that the multi-instance only contains automatic tasks and no wait states. In this situation, an asynchronous job is created when the multi-instance activity is entered that keeps checking if all instances are completed and completes the multi-instance. The benefit of this approach is that it is light on resources versus alternatives and doesn't lead to optimistic locking exceptions.

Details

Attribute	Type	Description	Category
Throw error if no rules were hit	Boolean	Determines whether an error should be thrown if no rules of the decision table were hit and consequently no result was found.	If checked, a runtime exception will be thrown when no rules are hit during the DMN rules evaluation. This will cause the current database transaction to roll back to the previous stable wait state.

Advanced

Execution

Attribute	Type	Description	Category
Skip expression	Text	If the Skip expression evaluates to true, the flow is taken regardless of any condition. It is required to opt-in to this feature by setting a variable _FLOWABLE_SKIP_EXPRESSION_ENABLED with the Boolean value true on the process instance.	When the Skip expression resolves to true, this decision task will not be executed at runtime. The Include in history flag can be used to store the historical entry of this decision task when running with a history level that normally would not store the execution of the service task. Note that this flag has no effect when running with history level 'none'.
Include in history	Boolean	When the history level is set to "instance" or "task" level with this property it can be configured if this activity instance should be included in the historic activity data.
Is for compensation	Boolean	Determines whether the activity can serve as a compensation for another activity.	A BPMN transaction is a set of activities that logically belongs together. Transactions can be cancelled through the Cancel End Event and handled through the Cancel Intermediate Boundary Event. The Is for compensation field can be used to indicate that the decision task is meant as compensation steps for another activity.
Asynchronous	Boolean	When enabled, the activity will be started as an asynchronous job. The process state is persisted before this element is executed. Then, the process execution will be resumed asynchroneously. This can be used when the execution an activity takes a long time to return the UI to the user quicker in case the user does not need to see the next step immediately. However, if an error occurs before the following wait state, there will be no direct user feedback. Please refer to the documentation for more details.	When making a decision task asynchronous, the DMN rules will be evaluated asynchronously in the background. This is useful for example to not block the UI of a user, in case of a large amount of complex rules. Choose exclusive to avoid other asynchronous steps of this process instance to run at the same time.
Exclusive	Boolean	Determines whether the activity or process is run as an exclusive job. An exclusive job makes sure that no other asynchronous exclusive activities within the same process are performed at the same time. This helps to prevent failing jobs in concurrent scenarios.
Leave asynchronously	Boolean	When enabled, the activity will be left as an asynchronous job. This means that the activity is ended asynchronously, including end execution listeners. Please refer to the documentation for more details.
Leave exclusive	Boolean	Determines whether the activity should leave as an exclusive job. An exclusive job makes sure that no other asynchronous exclusive activities within the same process are performed at the same time. This helps to prevent failing jobs in concurrent scenarios.
Job Category	Text	When set, the underlying generated job will have a Job Category, which will be executed only by Application Servers, where the Process Engine has enabledJobCategories set to this category.

Listeners

Attribute	Type	Description	Category
Execution listeners	List	Allows invoking custom after certain lifecycle events. Start: Executes after the activity has been started. End: Executes after the activity was completed. Transition: When defined on a sequence flow, executes once the flow is transition is taken.	Execution listeners are used to add logic on certain lifecycle events. Typically it is used to add extra technical logic which shouldn't be visible in the BPMN process model.

Visual

Attribute	Type	Description	Category
Background color	Color	The background color of the element in the diagram.	Visual properties that determine how the decision task is shown in the diagram. This has no impact on the runtime execution.
Font size	Selection: 8 9 10 11 12 14 18 20 24 36 48 72	Font size.
Font weight	Selection: Normal Bold	Select the style between bold and normal.
Font style	Selection: Normal Italic	Select the style between italic and normal.
Font color	Color	Select a font color.
Border color	Color	The border color of the element in the diagram.

List Attribute Details

Variable Aggregations

Attribute	Type	Description
Target (Variable / Expression)	Text	The name of the target variable or an expression that gives the variable name
Type	Selection: Default Custom	The type of aggregation. Use 'default' to use the standard behavior of creating an aggregation JSON variable. Use 'custom' to define a delegate expression that will handle the aggregation. Please see the documentation for more information.
Delegate Expression	Text	Define a delegateExpression that will resolve to an instance of VariableAggregator (for BPMN) or PlanItemVariableAggregator (for CMMN). This instance will then be responsible for aggregating the variables.
Class	String	A class that implements VariableAggregator (for BPMN) or PlanItemVariableAggregator (for CMMN). This instance will then be responsible for aggregating the variables.
Target variable creation	Selection: Default Create overview variable Store as transient variable	Configures the way the aggregation variable is created. The 'Default' option creates the aggregation variable when all instances of the multi-instance have been completed. Use 'Create overview variable' to create a variable at the start of the multi-instance and keep it up to date during multi-instance exeution. Once all the instances are completed it will create a JSON variable in the same way as for Default target variable creation. Use the 'Store as transient variable' option to have the default behavior, but store the resulting aggregation variable transiently.
Variable Definitions	BasicFormList	property.loopVariableAggregation.definitions.description

Variable Definitions

Attribute	Type	Description
Source (Variable / Expression)	Text	The name of the source variable or an expression that provides the value
Target (Variable / Expression)	Text	The name of the aggregation variable or an expression that resolves to a variable name.

Execution listeners

Attribute	Type	Description
Event	Selection: Start End Take	The lifecycle event. The 'Take' event is only available for sequence flow.
Class	Text	Fully qualified classname of a class to be invoked when executing the task. The class must implement either JavaDelegate or ActivityBehavior.
Expression	Text	JUEL Expression to be executed when the task is started. Expressions allow you to interact with the backend by calling services, making calculations etc. You can find more information about expressions in the documentation.
Delegate expression	Text	Delegate Expression to be executed when the task is started. A delegate expression must resolve to a Java object, for instance a Spring bean. The object's class must implement either JavaDelegate or ActivityBehavior.
Fields	List

Fields

Attribute	Type	Description
Name	Text	The name of the element. This is the name displayed in the diagram.
String value	Text
Expression	Text	JUEL Expression to be executed when the task is started. Expressions allow you to interact with the backend by calling services, making calculations etc. You can find more information about expressions in the documentation.
String	Text