A decision table is a tabular representation of a set of decision rules, with each decision rule indicating the resulting decision(s) for a combination of conditional expressions. Because of the tabular format, the order of the condition attributes in the conditional expressions is the same throughout the table.
Types of decision tables:
A distinction is made between single hit decision tables and multiple hit decision tables:
In a multiple hit decision table, decision rules are allowed to be non-exclusive. Non-exclusive (or overlapping) decision rules means that one decision case can match more than one decision rule. When non-exclusive decision rules are present, the order of the rules is often used to determine the appropriate rule (usually the first rule that applies).
A decision table is complete if all possible decision cases are covered in the decision rules.
Karnaugh Maps - http://en.wikipedia.org/wiki/Karnaugh