A decision table in software engineering is a powerful tool used to model and document complicated logic.
In software development and testing, dealing with complex business rules or conditions can be challenging. This is where decision tables come into play. As described, they are used to model complicated logic, providing a structured way to represent rules based on various conditions and their resulting actions.
Essentially, a decision table works by mapping different combinations of conditions to corresponding actions.
Key Aspects of Decision Tables
Based on the provided reference and general understanding, a decision table offers several benefits and characteristics:
- Modeling Complicated Logic: They excel at representing rules where multiple conditions interact to determine an outcome.
- Showing Combinations: A significant advantage is that it shows that all possible combinations of conditions have been considered. This helps ensure comprehensive coverage, whether for requirements definition or test case design.
- Clarity on Failed Conditions: When conditions are not met, it is easy to see which rules are not applicable or what outcome results from specific unmet criteria.
- Cause-Effect Representation: A decision table can be described as cause-effect table, linking the "causes" (conditions) directly to the "effects" (actions).
- Handling Combination Inputs/Outputs: It is the best way to deal with combination inputs with their associated outputs, making it ideal for scenarios with interdependent variables.
Structure of a Decision Table
A typical decision table is divided into four main parts:
- Condition Stub: Lists all the conditions relevant to the decision-making process.
- Condition Entries: Shows the different combinations of values (true/false, yes/no, specific ranges, etc.) that each condition can take. Each column in this section usually represents a unique rule or scenario.
- Action Stub: Lists all the possible actions that can be taken.
- Action Entries: Indicates which actions are performed for each rule (combination of condition entries).
Example Decision Table: Online Order Discount
Let's consider a simple example for applying a discount to an online order based on two conditions: "Is Customer a Member?" and "Is Order Total > $100?".
| Conditions | Rule 1 | Rule 2 | Rule 3 | Rule 4 |
|---|---|---|---|---|
| Is Customer a Member? | Yes | Yes | No | No |
| Is Order Total > $100? | Yes | No | Yes | No |
| Actions | ||||
| Apply 10% Discount | X | |||
| Apply 5% Discount | X | |||
| No Discount | X | X | ||
| Send 'Thank You' Email | X | X | X | X |
In this table:
- Conditions are the rows in the top section.
- Actions are the rows in the bottom section.
- Rule 1 states: If the customer is a member AND the order total is > $100, THEN apply a 10% discount and send a 'Thank You' email.
- Rule 4 states: If the customer is NOT a member AND the order total is NOT > $100, THEN no discount is applied, but a 'Thank You' email is still sent.
This table clearly lays out all four possible combinations of the two conditions and the corresponding actions for each.
Benefits in Software Engineering
Decision tables are valuable for:
- Requirements Analysis: Helping business analysts clarify complex business rules and ensure all scenarios are covered.
- Development: Providing developers with a clear specification of the logic to implement.
- Testing: Serving as a basis for designing comprehensive test cases, ensuring that every rule and condition combination is tested.
They bring structure, clarity, and completeness to handling intricate logical dependencies.
