Creating a Decision Model

In the model we described in An Example of Decision Modeling, we showed how a decision can be modeled using a Decision Table, in which a decision result is determined by finding a row in the table where the input values in the table match the input values under consideration, giving a particular output result.

We will now look at how such a model can be created in Enterprise Architect, by stepping through the process of creating the decision model for the Airline Cabin Upgrade example.

There are a number of model elements involved in this example, such as Input Data elements, Item Definitions that are used to describe the Input Data (defining the data types), a Decision element and also a Business Knowledge Model element that holds the Decision Table definition.

Create a Decision Requirements Diagram

These steps will guide you through the creation of a simple Decision Requirements Diagram (DRD).  In this example, we will create the model from scratch, rather than using a pattern from the Model Wizard.

At this stage, we should have a simple DRD, that resembles this:

We can now specify the details for each of the elements making up this model.

Define the Decision Table

By double-clicking on the Business Knowledge Model element 'Cabin Upgrade Policy', the 'DMN Expression' window is displayed, showing an empty Decision Table. This is where we will define the rules of our cabin upgrade policy.

By default, new Decision Tables are created with two input columns and one output column, a header row and three empty rules rows.

The left-most column in the table displays the Hit Policy and also numbers the rules. By default, the Hit Policy is 'U' for 'Unique'. This is the policy that we will use for our example, so you do not need to change this column heading. 

For more information on Hit Policies, refer to the Decision Table Hit Policy Help topic.

Name and Define Types for Decision Table Inputs and Outputs

Define the Rules of the Decision Table

Enter values into the table cells to match this image.

Click on a cell to select it, and click again to edit it.

You can copy and paste existing rules by selecting the rows to copy (Shift+click adds to the selection), right-click and choose 'Copy', then right-click and choose 'Append'.

Once you have finished editing the rules, click on the Save button .

Finally, click the Validate button ,  to check for errors in the table of rules.

Create ItemDefinition Elements

Add two ItemDefinition elements to the diagram, one for each of the InputData elements.  Name one element 'CustomerDefinition' and the other 'CabinStatusDefinition'.

Double-click the ItemDefinition named 'CustomerDefinition' to edit the definition.  The DMN Expression window is displayed.

Right-click on the cell 'CustomerDefinition' and choose 'Add Child Component'.  Overtype the name of the child component with 'Num of Flights in Last Month' and overtype its datatype  with 'number'.  Click the 'Save' button to save the changes, and close the window.

Similarly, double-click on the ItemDefinition named 'CabinStatusDefinition', add a child component named 'Num of Pax Overbooked' and set its data type to 'number'.  Save the changes and close the window.

Specify the Data Type For Each InputData Element

Select the InputData element 'Customer'.  In the Properties window,  select the property 'typeRef' and click on the button.

Select the ItemDefinition 'Customer Definition' as the type.  Click on 'OK'.

Similarly, specify 'Cabin Status Definition' as the type for 'Cabin Status'.

Specify the Inputs to the Decision Element

Double-click on the decision element 'Determine Cabin for Upgrade'

In the DMN Expression window, locate the table row containing the text 'Num of Pax Overbooked' in the first column.  Click in the cell in the second column of this row, and press the Spacebar.  A list of possible input values is displayed.  Choose 'Cabin Status . Num of Pax Overbooked' and press 'Enter'.  The selection is written into the cell.

Repeat this process for the second table row 'Num of Flights in Last Month', choosing 'Customer . Num of Flights in Last Month'.

Click on the Save button.

Click on the Validate button.

Define Data Sets

The 'correctness' of your decision model can be tested, by running simulations using a range of representative data sets to verify that the model produces the correct result in all situations.

You can create numerous Data Sets with various names, using a range of data values.  You can set one of the data sets as the default value.

We will now create a Data Set for each of our InputData elements.

Add a DMNSimConfiguration Artifact

Locate the DMN 'Simulation Configuration' Artifact in the Diagram Toolbox.  Drop one of these onto the diagram as well.

Double-click on it to open the DMN Simulation window at the 'Simulate' tab.

From the DMN Simulation window, you can run simulations of the completed Decision Model.  You can also perform validation, generate code and generate test modules.

Learn more

• Decision Table Hit Policy