Each row of a decision table corresponds to one rule:

To make the rows of decision tables more intuitive to read, cells that are shared by more than one rule are merged:

In this table, both rules have the same value for the first condition but a different value for the second condition, as follows:

A third rule added to this decision table can either:

Also, you can add an `Otherwise' row to take into account the case where none of the other possibilities for that condition are correct.

Partitioned Cells

Groups of cells that are in the same condition column and have a common cell immediately to the left are referred to as partitions.

Partitions let you easily pick out any missing or overlapping rules in your tables:

In a decision table, each cell in the left-most column represents the first condition to be considered. Then, for each of these cells, the next column should contain a group of cells (partition) that cover all possible values for that column. If it does not, the table may be incomplete.

Similarly, if there are additional columns, the same rule applies: the third column should contain groups of cells that cover all possible values for that column.

Empty Cells

It is possible for a row to 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. The fourth rule above would simply not consider the second action.