Literal Expression

A Literal Expression is the simplest form of DMN expression. It is commonly defined as a single-line statement or an if-else conditional block. When the expression is getting complicated, you might prefer a Boxed Context, or in order to improve the readability you can encapsulate some logic as a function in the DMN Library. See the example at the end of this page.

Access

Toolbar Options

Options	Description	See also
	Click on this button to save the configuration to the current Decision or BusinessKnowledgeModel.
	Click on this button to edit parameters for the Business Knowledge Model.
	This option is disabled for Literal Expressions.
	This option is disabled for Literal Expressions.
	This option is disabled for Literal Expressions.
	This option is disabled for Literal Expressions.
	Click on this button to validate the Literal Expression. Enterprise Architect will perform a series of validations to help you locate errors in the Expression.	DMN Expression Validation
	This button is enabled when the literal expression is defined for a BusinessKnowledgeModel.	BusinessKnowledgeModel & Test Harness

Example — Payment of 2 Decimals

This Business Knowledge Model (BKM) Payment_2_decimal is implemented as a Literal Expression.

• The BKM defines three parameters: Rate, Term and Principle

Give values for the Test Harness and evaluate the model:

• The runtime parameter value will be displayed; for example, Rate = 00.005
• The BKM's result will be evaluated by the literal expression and the value is displayed on the declaration line; for example, return = 1798.65

Although the implementation is one line, it is quite complicated. We can re-factor this model with Built-In function and Boxed Context to improve readability:

• The Boxed Context defines two variable-expression paired entries; these variables serve as 'local variables', which can be used in later expressions
• Return value: the expression can use the value of 'local variables'
• Any expressions in a Boxed Context can use built-in functions that are defined in the customizable Template — DMN Library; for example, functions PMT(...) and decimal(...) are used in this example

The simulation result is exactly the same as a Literal Expression:

Expression Editor and Intelli-sense Support

In accordance with the FEEL language specification, the parameter names can contain spaces. This feature makes the expression easier to read. Enterprise Architect also provides Intelli-sense support for editing the expressions with minimal typing and fewer mistakes.

Given a decision hierarchy such as this, the expression in 'Decision3' should be able to use the required decisions (variables).

Right-click on the Expression  and select the menu option 'Edit Expressions...' to display the 'Expression' dialog.

Press Ctrl+Space to show the Intelli-sense menu:

• For 'BKM', all the parameters will be included
• For 'Decision', all the required Decisions will be included

The DMN Model can be generated as source code in JavaScript, Java, C# or C++; since some languages might have different syntax for some expressions, Enterprise Architect provides language override pages for each language. If no override code is specified for a language, the expression defined for the FEEL language will be used.

In the generated code, the space inside a variable name will be replaced by an underscore.

Learn more

• DMN Expression Validation
• Business Knowledge Model & Test Harness