Sometimes, it is convenient to describe a system as a set of possible conditions satisfied by the system at a given time, rules for reacting to stimuli when certain sets of those conditions are met, and actions to be taken as a result.
Decision tables provide a mechanism for recording complex decision logic. Decision tables are widely used in data processing applications and have an extensively developed literature. As illustrated in Table a decision table is segmented into four quadrants : condition stub, condition entry, action stub, and action entry.
The condition stub contains all of the conditions being examined. Condition entries are used to combine conditions into decision rules. The action stub describes the actions to be taken in response to decision rules, and the action entry quadrant relates decision rules to actions.
Table illustrates the format of limited-entry decision table (entries are limited to Y, N,
, and X). In a limited-entry decision table, Y denoted “yes”, N denotes “no” denotes “don’t care,” and X denoted “perform action.” According to Table, orders are approved if the credit limit is not exceeded, or if the credit limit is exceeded but past experience is good, or if a special arrangement has been made. If none of these conditions hold, the order is rejected.
The (Y, N, –) entries in each column of the condition entry quadrant from a decision rule. If more than one decision rules has identical (Y, N, –) entries, the table is said to be ambiguous. Ambiguous pairs of decision rules that specify identical actions are said to be redundant, and those specifying different actions are contradictory. Contradictory rules permit specification of non deterministic and concurrent actions. Table illustrates redundant rules (R3 and R4) and contradictory rules (R2 and R3, and R2 and R4).
Advantages of Decision Table
The various advantages of decision table are depicted as follows :
(I) Consistency in decisions making
- Decision rules are clearly structured
- Documentation is easily prepared, changed or updated
- Managers can be relieved from decision-making
- Easy to use
- Facilitate more compact documentation
- Communication is easier between manager and analysis
- Easier to follow a particular path down one column than through complex and lengthy flowcharts.
- Easier to draw or modify in comparison to flowcharts.
Disadvantages of Decision Table
The various disadvantages of decision table are as follows :
- Does not depict the flow
- Cannot list all the alternatives
- Not easy to translate it
- Impose an additional burden