Business Knowledge Model & Test Harness

A Business Knowledge Model encapsulates logic without reflecting the usage context. It is implemented as a function definition, with parameters and a DMN expression as body (such as Decision table, Boxed Context or Literal Expressions).

Because the definition of a Business Knowledge Model is self-contained, it is possible to perform 'Unit Testing' by providing arguments for the parameters. For this reason, a Business Knowledge Model will have an 'Input Parameter Values for Simulation' tab in the DMN Expression window.

Parameters of a Business Knowledge Model

In the DMN Expression window, click on the Edit Parameters button on the toolbar to open the 'Edit Parameters' dialog:

You can perform these actions on the parameters:

• Add a new parameter by typing in the 'New Parameter...' row
• Delete an existing parameter using the context menu
• Modify the name of the existing parameter by in-place editing in the cell
• Change the type of the existing parameter

Test Harness

The Business Knowledge Models (BKMs) described in this section are available from the Model Wizard (Ctrl+Shift+M); select the Requirements | Decision Modeling page.

Decision Table

Example Access:

• Create pattern for 'DMN Decision | A Complete Example'
• Navigate in the Project Browser to 'A Complete Example | Business Knowledge Models | Eligibility rules'
• Double-click on the 'Eligibility rules' element to open the BKM in the DMN Expression window

When a Decision table is created for a Business Knowledge Model, we can test this BKM by binding some values:

We can provide test values such as these:

Click on the Run button on the tool bar; this result is obtained:

• The runtime parameter value will take the place of 'Allowed Values' in simulation mode
• Valid rule(s) are highlighted
• Since this Decision table's hit policy is P (Priority) the final result is determined by the order of 'output values'; since 'INELIGIBLE' and 'ELIGIBLE' are the output values and 'INELIGIBLE' comes ahead of 'ELIGIBLE', rule #3 will give the final result and this applicant is 'INELIGIBLE'.

Boxed Context / Literal Expressions

Example Access:

• Create the pattern for 'DMN Business Knowledge Model | Business Knowledge Model Literal Expression'
• Navigate in the Project Browser to 'Business Knowledge Model Literal Expression | Payment'

Double-click on the 'Payment' element to open the BKM in the DMN Expression window

Similar to Decision table, the Business Knowledge Model implemented as a Boxed Expression can be tested as well.

Take this 'Payment_2_decimal' BKM as an example:

This BKM will calculate the monthly repayment based on interest rate, number of terms and principal amount.

We could provide test values such as these:

Click on the Run button on the tool bar; this result is obtained:

The runtime parameter and return value will be displayed with an equals sign '=', followed by the runtime value.

In this example, given an annual Rate of 4% for 30 years and a principal of $300,000, the monthly repayment is $1,432.25

Note: The DMN Library already has a PMT function defined; this example mainly demonstrates how Literal Expression works and how to test it with a set of arguments.