Chapter 3. Decision Model and Notation (DMN)
Decision Model and Notation (DMN) is a standard established by the Object Management Group (OMG) for describing and modeling operational decisions. DMN defines an XML schema that enables DMN models to be shared between DMN-compliant platforms and across organizations so that business analysts and business rules developers can collaborate in designing and implementing DMN decision services. The DMN standard is similar to and can be used together with the Business Process Model and Notation (BPMN) standard for designing and modeling business processes.
For more information about the background and applications of DMN, see the OMG Decision Model and Notation specification.
3.1. Creating the traffic violations DMN decision requirements diagram (DRD)
A decision requirements diagram (DRD) is a visual representation of your DMN model. Use the DMN designer in Business Central to design the DRD for the traffic violations project and to define the decision logic of the DRD components.
Figure 3.1. DRD for the Traffic Violations example
Prerequisites
- You have created the traffic violations project in Business Central.
Procedure
- On the traffic-violation project’s home page, click Add Asset.
On the Add Asset page, click DMN. The Create new DMN window is opened.
-
In the Create new DMN window, enter
Traffic Violation
in the DMN name field. -
From the Package list, select
com.myspace.traffic_violation
. - Click Ok. The DMN asset in the DMN designer is opened.
-
In the Create new DMN window, enter
In the DMN designer canvas, drag two DMN Input Data input nodes on to the canvas.
Figure 3.2. DMN Input Data nodes
- In the upper-right corner, click the Properties icon.
-
Double-click each input node, and in the Name field, rename one to
Driver
and the other toViolation
. - Drag a DMN Decision decision node on to the canvas.
-
Double-click the decision node and rename it to
Fine
. Click the Violation input node, select the Create DMN Information Requirement icon and click the
Fine
decision node to link the two nodes.Figure 3.3. Create DMN Information Requirement icon
- Drag a DMN Decision decision node on to the canvas.
-
Double-click the decision node and rename it to
Should the driver be suspended?
. - Click the Driver input node, select the Create DMN Information Requirement icon and click the Should the driver be suspended? decision node to link the two nodes.
- Click the Fine decision node, select the Create DMN Information Requirement icon, and select the Should the driver be suspended? decision node.
Click Save.
NoteAs you periodically save a DRD, the DMN designer performs a static validation of the DMN model and might produce error messages until the model is defined completely. After you finish defining the DMN model completely, if any errors remain, troubleshoot the specified problems accordingly.
3.2. Creating the traffic violations DMN custom data types
DMN data types determine the structure of the data that you use within a table, column, or field in a DMN boxed expression for defining decision logic. You can use default DMN data types (such as string, number, or boolean) or you can create custom data types to specify additional fields and constraints that you want to implement for the boxed expression values. Use the DMN designer’s Data Types tab in Business Central to define the custom data types for the traffic violations project.
Figure 3.4. The custom data types tab
The following tables list the tDriver
, tViolation
, and tFine
custom data types that you will create for this project.
Name | Type |
---|---|
tDriver | Structure |
Name | string |
Age | number |
State | string |
City | string |
Points | number |
Name | Type |
---|---|
tViolation | Structure |
Code | string |
Date | date |
Type | string |
Speed Limit | number |
Actual Speed | number |
Name | Type |
---|---|
tFine | Structure |
Amount | number |
Points | number |
Prerequisites
- You created the traffic violations DMN decision requirements diagram (DRDs) in Business Central.
Procedure
-
To create the
tDriver
custom data type, click Add a custom Data Type on the Data Types tab, entertDriver
in the Name field, and selectStructure
from the Type list. Click the check mark to the right of the new data type to save your changes.
Figure 3.5. The tDriver custom data type
Add each of the following nested data types to the
tDriver
structured data type by clicking the plus sign next totDriver
for each new nested data type. Click the check mark to the right of each new data type to save your changes.-
Name
(string) -
Age
(number) -
State
(string) -
City
(string) -
Points
(number)
-
-
To create the
tViolation
custom data type, click New Data Type, entertViolation
in the Name field, and selectStructure
from the Type list. Click the check mark to the right of the new data type to save your changes.
Figure 3.6. The tViolation custom data type
Add each of the following nested data types to the
tViolation
structured data type by clicking the plus sign next totViolation
for each new nested data type. Click the check mark to the right of each new data type to save your changes.-
Code
(string) -
Date
(date) -
Type
(string) -
Speed Limit
(number) -
Actual Speed
(number)
-
To add the following constraints to the
Type
nested data type, click the edit icon, click Add Constraints, and select Enumeration from the Select constraint type pull-down menu.-
speed
-
parking
-
driving under the influence
-
- Click OK, then click the check mark to the right of the Type data type to save your changes.
To create the
tFine
custom data type, click New Data Type, entertFine
in the Name field, selectStructure
from the Type list, and click Save.Figure 3.7. The tFine custom data type
Add each of the following nested data types to the
tFine
structured data type by clicking the plus sign next totFine
for each new nested data type. Click the check mark to the right of each new data type to save your changes.-
Amount
(number) -
Points
(number)
-
- Click Save.
3.3. Assigning custom data types to the DRD input and decision nodes
After you create the DMN custom data types, assign them to the appropriate DMN Input Data and DMN Decision nodes in the traffic violations DRD.
Prerequisites
- You have created the traffic violations DMN custom data types in Business Central.
Procedure
- Click the Model tab on the DMN designer and click the Properties icon in the upper-right corner of the DMN designer to expose the DRD properties.
-
In the DRD, select the Driver input data node and in the Properties panel, select
tDriver
from the Data type pull-down menu. -
Select the Violation input data node and select
tViolation
from the Data type pull-down menu. -
Select the Fine input data node and select
tFine
from the Data type pull-down menu. Select the Should the driver be suspended? decision node and set the following properties:
-
Data type:
string
-
Question:
Should the driver be suspended due to points on his driver license?
-
Allowed Answers:
Yes,No
-
Data type:
- Click Save.
You have assigned the custom data types to your DRD’s input and decision nodes.
3.4. Defining the traffic violations DMN decision logic
To calculate the fine and to decide whether the driver is to be suspended or not, you can define the traffic violations DMN decision logic using a DMN decision table and context boxed expression.
Figure 3.8. Fine decision table
Figure 3.9. Should the driver be suspended?
Prerequisites
- You have assigned the DMN custom data types to the appropriate decision and input nodes in the traffic violations DRD in Business Central.
Procedure
To calculate the fine, in the DMN designer canvas, select the Fine decision node and click the Edit icon to open the DMN boxed expression designer.
Figure 3.10. Decision node edit icon
Click Select expression
Decision Table. Figure 3.11. Select Decisiong Table logic type
- For the Violation.Date, Violation.Code, and Violation.Speed Limit parameter fields, right-click and select Delete for each field.
-
Click the Violation.Actual Speed column header and enter the expression
Violation.Actual Speed - Violation.Speed Limit
in the Name field. -
Right-click the Fine parameter field and select either
Insert left
orInsert right
. -
Click the output-2 column sub-header, enter
Amount
in the Name field, and selectnumber
from the Data Type pull-down menu. -
Similarly, click the output-1 column sub-header, enter
Points
in the Name field, and selectnumber
from the Data Type field. Next, enter the following values in the first row of the decision table:
-
Violation.Type:
"speed"
-
Violation.Actual Speed - Violation.Speed Limit:
[10..30)
-
Amount:
500
Points:
3
Right-click the first row and select
Insert below
to add another row.
-
Violation.Type:
Enter the following values in the second row of the decision table:
-
Violation.Type:
"speed"
-
Violation.Actual Speed - Violation.Speed Limit:
>= 30
-
Amount:
1000
Points:
7
Right-click the second row and select
Insert below
to add another row.
-
Violation.Type:
Enter the following values in the third row of the decision table:
-
Violation.Type:
"parking"
-
Violation.Actual Speed - Violation.Speed Limit:
-
-
Amount:
100
Points:
1
Right-click the third row and select
Insert below
to add another row.
-
Violation.Type:
Enter the following values in the fourth row of the decision table:
-
Violation.Type:
"driving under the influence"
-
Violation.Actual Speed - Violation.Speed Limit:
-
-
Amount:
1000
-
Points:
5
-
Violation.Type:
- Click Save.
- To define the driver suspension rule, return to the DMN designer canvas, select the Should the driver be suspended? decision node, and click the Edit icon to open the DMN boxed expression designer.
-
Click Select expression
Context. -
Click ContextEntry-1, enter
Total Points
as the Name, and selectnumber
from the Data Type pull-down menu. -
Click the cell next to Total Points, select
Literal expression
from the context menu, and enterDriver.Points + Fine.Points
as the expression. -
In the cell below Driver.Points + Fine.Points, select
Literal Expression
from the context menu, and enterif Total Points >= 20 then "Yes" else "No"
. Click Save.
You have defined how to calculate the fine and the context for deciding when to suspend the driver. You can navigate to the traffic-violation project page and click Build to build the example project and address any errors noted in the Alerts panel.