Each row in a decision table corresponds to a rule.
| Grade | Amount of loan | Insurance required | Insurance rate | ||
|---|---|---|---|---|---|
| Min | Max | ||||
| 1 | A | 100,000 | 300,000 | true | 0.001 |
To make the rows of decision tables more intuitive to read, cells that are shared by more than one rule are merged.
| Grade | Amount of loan | ||
|---|---|---|---|
| Min | Max | ||
| 1 | A | 100,000 | 300,000 |
| 2 | 300,000 | 600,000 | |
In this table, each row corresponds to a rule, and they share a condition.
Rule 1
if
all of the following conditions are true:
- the loan grade is A
- the amount of loan is at least 100000 and less than 300000
Rule 2
if
all of the following conditions are true:
- the loan grade is A
- the amount of loan is at least 300000 and less than 600000
A third row added to this decision table can either:
Have a different value for the first condition:
| Grade | Amount of loan | ||
|---|---|---|---|
| Min | Max | ||
| 1 | A | 100,000 | 300,000 |
| 2 | 300,000 | 600,000 | |
| 3 | B | 100,000 | 300,000 |
Share the value for the first condition:
| Grade | Amount of loan | ||
|---|---|---|---|
| Min | Max | ||
| 1 | A | 100,000 | 300,000 |
| 2 | 300,000 | 600,000 | |
| 3 | 600,000 | 900,000 | |
Also, you can add an Otherwise row to take into account the case where none of the other possibilities for that condition are correct.
In condition columns, you can merge or split the cells under subcolumns and change the operator. For example, the third row in the following table also deals with Age, but with the operator is more than, which has one value, instead of is between, which requires two:
| Age | ||
|---|---|---|
| Min | Max | |
| 1 | 18 | 25 |
| 2 | 26 | 40 |
| 3 | >40 | |
A partition is a group of cells in a condition column with a common cell next to them. In the following table, cells A and B in the Grade column each have a partition of cells in the Amount of loan column.
Partitions are important to consider when adding new rows, when sorting columns, and to understand error messages displayed in the decision table.
| Grade | Amount of loan | Insurance required | Insurance rate | ||
|---|---|---|---|---|---|
| Min | Max | ||||
| 1 | A | <100,000 | false | ||
| 2 | 100,000 | 300,000 | true | 0.001 | |
| 3 | 300,000 | 600,000 | true | 0.003 | |
| 4 | ≥600,000 | true | 0.005 | ||
| 5 | B | <100,000 | false | ||
| 6 | 100,000 | 300,000 | true | 0.0025 | |
| 7 | 300,000 | 600,000 | true | 0.005 | |
| 8 | 600,000 | 800,000 | |||
| 9 | ≥600,000 | true | 0.0075 | ||
In a decision table, each cell in the first column represents the first condition. For each of these cells, the next column contains a cell or group of cells (partition) that cover all possible values for that column. If it does not, the table might be incomplete.
Similarly, if there are additional columns, the same rule applies: the third column contains groups of cells that cover all possible values for that column.
A row can contain empty cells. When the empty cell is in a condition column, the condition is always satisfied. When the empty cell is in an action column, the action is ignored.
| Grade | Amount of loan | Insurance required | Insurance rate | ||
|---|---|---|---|---|---|
| Min | Max | ||||
| 1 | A | <100,000 | false | ||
| 2 | 100,000 | 300,000 | true | 0.001 | |
| 3 | 300,000 | 600,000 | true | 0.003 | |
| 4 | ≥600,000 | true | 0.005 | ||
For example, the first rule in this table would not set an Insurance rate.