A Decision Tables is a tool used to model complex decision-making processes. It helps in representing and analyzing rules, conditions, actions, and their interrelationships. Decision tables are widely used in software engineering, business rule analysis, and logic modeling, particularly when dealing with a large number of possible scenarios that can influence a decision. They provide a systematic approach to making decisions based on multiple conditions and actions.
Components of a Decision Table
A decision table is typically divided into four main components:
- Conditions:
- These are the inputs or criteria that influence the decision. Conditions can have binary (Yes/No) or multiple states.
- Example: “Is the customer a premium member?” or “Is the order above $100?”
- Actions:
- These are the outcomes or results that are performed based on the conditions. Actions are the possible responses or operations that follow the decision-making process.
- Example: “Apply discount,” “Reject order,” “Send confirmation email.”
- Condition Entries:
- This section specifies the possible values or states for each condition. A condition entry can either represent a specific state (e.g.,
TrueorFalse,YesorNo) or a list of possibilities in more complex scenarios.
- This section specifies the possible values or states for each condition. A condition entry can either represent a specific state (e.g.,
- Action Entries:
- This section defines which actions will be taken based on the various condition combinations. If the condition entries meet the criteria in a given rule, the corresponding action is triggered.
Structure of a Decision Table
A decision table typically consists of four quadrants:
- Condition Stub: This lists all the conditions that need to be checked.
- Action Stub: This lists all the actions to be performed if the conditions are met.
- Condition Entries: These specify all the possible combinations of conditions.
- Action Entries: These indicate which actions are triggered for each condition combination.
A simple example:
| Condition Stub | Condition 1 | Condition 2 | Condition 3 | Action Stub | Action 1 | Action 2 |
|---|---|---|---|---|---|---|
| Rule 1 | Yes | Yes | No | Action 1 | Apply Discount | No Discount |
| Rule 2 | Yes | No | Yes | Action 2 | Send Email | No Email |
| Rule 3 | No | Yes | Yes | Action 1 | Apply Discount | No Discount |
| Rule 4 | No | No | No | Action 2 | Send Email | No Email |
In this example:
- Condition 1 could represent “Is the customer a premium member?”
- Condition 2 could represent “Is the order value greater than $100?”
- Condition 3 could represent “Is the customer in a special promotion?”
- Action 1 could represent “Apply discount.”
- Action 2 could represent “Send email.”
Interpretation:
- Rule 1: If both Condition 1 and Condition 2 are
Yesand Condition 3 isNo, then Action 1 (Apply Discount) is executed. - Rule 2: If Condition 1 is
Yes, Condition 2 isNo, and Condition 3 isYes, then Action 2 (Send Email) is executed. - Rule 3: If Condition 1 is
No, Condition 2 isYes, and Condition 3 isYes, then Action 1 (Apply Discount) is executed. - Rule 4: If all conditions are
No, then Action 2 (Send Email) is executed.
Types of Decision Tables
There are two main types of decision tables based on how conditions and actions are organized:
- Limited Entry Decision Table:
- In this type, conditions are typically binary (Yes/No, True/False).
- Each rule is a combination of conditions, and actions are either performed or not, depending on the rule.
- Extended Entry Decision Table:
- This type allows for more complex decision-making with conditions that have multiple states, not just binary options.
- It can involve a larger number of rules and more complex combinations of actions.
Steps to Create a Decision Table
- Identify the Conditions:
- List all the conditions or criteria that affect the decision-making process.
- Each condition can have multiple values (for example, yes/no, true/false, high/low, etc.).
- List the Actions:
- Identify the actions or outcomes that should be executed based on the conditions.
- Each action is the result of one or more conditions being met.
- Fill in the Condition Entries:
- Determine all possible combinations of the conditions. For each combination, assign values to the corresponding condition entries.
- Define the Action Entries:
- For each combination of conditions, specify which actions should be executed.
- If the conditions in a rule are met, the corresponding actions are triggered.
- Review the Decision Table:
- Ensure that all possible condition combinations are covered, and the correct actions are specified.
Benefits of Using Decision Tables
- Clarity and Structure:
- Decision tables provide a clear, structured way of representing complex decision logic, making it easier to understand and communicate.
- Avoids Ambiguity:
- By mapping out all possible conditions and actions in a table, ambiguity is reduced, and all possible scenarios are accounted for.
- Error Reduction:
- Decision tables help identify missing conditions or conflicting rules, thus reducing errors in decision logic.
- Easy Maintenance:
- When business rules or conditions change, it is easier to modify the decision table than to change multiple decision-making algorithms.
- Test Case Generation:
- Decision tables can be used to generate test cases for validating that the system behaves as expected under all possible conditions.
Example: Decision Table for Loan Approval
Consider the following scenario where a bank uses a decision table to determine whether a loan application is approved or rejected based on the applicant’s credit score and monthly income.
- Condition 1: Credit score is above 700?
- Condition 2: Monthly income above $5000?
Actions:
- Action 1: Approve loan
- Action 2: Reject loan
| Condition Stub | Condition 1 (Credit Score > 700) | Condition 2 (Income > $5000) | Action Stub | Action 1 (Approve Loan) | Action 2 (Reject Loan) |
|---|---|---|---|---|---|
| Rule 1 | Yes | Yes | Action 1 | Approve | |
| Rule 2 | Yes | No | Action 2 | Reject | |
| Rule 3 | No | Yes | Action 2 | Reject | |
| Rule 4 | No | No | Action 2 | Reject |
Interpretation:
- Rule 1: If the credit score is above 700 and the monthly income is above $5000, the loan is approved.
- Rule 2: If the credit score is above 700 but the monthly income is below $5000, the loan is rejected.
- Rule 3: If the credit score is below 700 but the monthly income is above $5000, the loan is rejected.
- Rule 4: If both the credit score is below 700 and the monthly income is below $5000, the loan is rejected.
Advanced Use Case: Decision Table for Shipping Cost Calculation
For an e-commerce platform, the shipping cost calculation could depend on conditions like the total order value, delivery method, and whether the customer is a premium member.
- Condition 1: Is the order value above $100?
- Condition 2: Is the delivery method standard or express?
- Condition 3: Is the customer a premium member?
Actions:
- Action 1: Free shipping
- Action 2: Standard shipping fee
- Action 3: Express shipping fee
| Condition Stub | Condition 1 (Order > $100) | Condition 2 (Delivery Method) | Condition 3 (Premium Member) | Action Stub | Action 1 (Free Shipping) | Action 2 (Standard Shipping Fee) | Action 3 (Express Shipping Fee) |
|---|---|---|---|---|---|---|---|
| Rule 1 | Yes | Standard | Yes | Action 1 | Free Shipping | ||
| Rule 2 | Yes | Express | Yes | Action 1 | Free Shipping | ||
| Rule 3 | Yes | Standard | No | Action 2 | Standard Fee | ||
| Rule 4 | Yes | Express | No | Action 3 | Express Fee | ||
| Rule 5 | No | Standard | Yes | Action 2 | Standard Fee | ||
| Rule 6 | No | Express | Yes | Action 3 | Express Fee | ||
| Rule 7 | No | Standard | No | Action 2 | Standard Fee | ||
| Rule 8 | No | Express | No | Action 3 | Express Fee |
Suggested Questions
Basic Conceptual Questions
- What is a decision table, and why is it used in decision-making?
- A decision table is a tabular representation of decision logic, used to model complex decision-making processes by organizing conditions and actions. It helps in systematically evaluating different combinations of conditions and determining the corresponding actions. It is particularly useful when many conditions interact to determine the outcomes.
- List and explain the four main components of a decision table.
- Condition Stub: Lists the conditions or criteria that influence the decision.
- Action Stub: Lists the actions or outcomes that are triggered by specific condition combinations.
- Condition Entries: Specifies the possible states or values of the conditions (e.g., Yes/No, True/False).
- Action Entries: Specifies the actions to be taken for each combination of conditions.
- Differentiate between a limited entry decision table and an extended entry decision table.
- Limited Entry Decision Table: The conditions are binary (Yes/No, True/False) and thus lead to simpler, more straightforward decision tables.
- Extended Entry Decision Table: The conditions can have multiple states (e.g., Low, Medium, High) and can involve more complex decision-making processes with a larger number of possible outcomes.
- How can decision tables help reduce ambiguity in decision-making processes?
- Decision tables provide a clear and structured way to represent decision logic, reducing ambiguity by explicitly defining which actions should be taken under all possible combinations of conditions. This eliminates misinterpretation or inconsistency in decision-making.
- What is the role of condition entries and action entries in a decision table?
- Condition Entries: Represent the possible values or states of each condition. They show the criteria that need to be checked.
- Action Entries: Define the actions that are performed when the corresponding condition combinations are met.
Intermediate Application-Based Questions
- Consider the following conditions for an online store’s discount policy:
- Condition 1: Is the customer a premium member? (Yes/No)
- Condition 2: Is the order value above $100? (Yes/No)
- Action 1: Apply a 10% discount
- Action 2: Apply a 5% discount
- Action 3: No discount
- Rule 1: If the customer is a premium member and the order value is above $100, a 10% discount is applied.
- Rule 2: If the customer is a premium member and the order value is not above $100, a 5% discount is applied.
- Rule 3: If the customer is not a premium member and the order value is above $100, a 5% discount is applied.
- Rule 4: If neither condition is met, no discount is applied.
- Explain how you would convert a set of business rules for an employee bonus system into a decision table. The conditions are:
- Condition 1: Is the employee’s performance rating above 4? (Yes/No)
- Condition 2: Is the employee’s work tenure more than 5 years? (Yes/No)
- Action 1: Award bonus
- Action 2: No bonus
- Rule 1: If the performance rating is above 4 and the tenure is more than 5 years, a bonus is awarded.
- Rule 2: If the performance rating is above 4 (regardless of tenure), a bonus is awarded.
- Rule 3: If the performance rating is below 4 and the tenure is more than 5 years, no bonus is awarded.
- Rule 4: If both conditions are not met, no bonus is awarded.
- How does a decision table help in generating test cases for software testing? Provide an example.
- A decision table helps by listing all possible condition combinations and their corresponding actions. These combinations serve as test cases to ensure that the software behaves as expected under all scenarios. For example, in an online payment system, you could use a decision table to test various combinations of payment methods (credit card, PayPal, etc.) and whether the transaction is approved or rejected.
Advanced Scenario-Based Questions
- You are designing a decision table for an online loan approval system. The conditions are as follows:
- Condition 1: Is the applicant’s credit score above 700? (Yes/No)
- Condition 2: Does the applicant have a steady monthly income? (Yes/No)
- Condition 3: Is the applicant applying for a loan greater than $50,000? (Yes/No)
- Action 1: Approve loan
- Action 2: Reject loan
- Action 3: Request more information
- Rule 1: If the credit score is above 700, income is steady, and the loan is above $50k, approve the loan.
- Rule 2: If the credit score is above 700 and income is steady, approve the loan even if the loan is not above $50k.
- Rule 3 & 4: If the credit score is above 700 but income is not steady, request more information.
- Rules 5 to 8: If the credit score is not above 700, reject the loan regardless of the other conditions.
Advanced Logic Questions
- What are the advantages of using decision tables over decision trees in some complex decision-making scenarios?
- Decision tables provide a more compact and easier-to-read representation of decision logic compared to decision trees, especially when there are multiple conditions and actions. They can represent conditions in a tabular format, which is easier to compare and analyze. In contrast, decision trees can become unwieldy and difficult to interpret when dealing with many conditions.
- Describe how you would handle conflicting actions in a decision table. How do you prioritize actions when multiple actions are triggered by a condition combination?
- In a decision table, conflicting actions can be handled by establishing clear priorities for each action, using predefined business rules or logic. One approach is to assign a priority level to each action and apply the highest-priority action in case of conflicts. Another approach is to ensure that actions are mutually exclusive or logically consistent.
- Explain the process of simplifying a decision table. How can a decision table be reduced to minimize redundant rules or actions?
- Simplifying a decision table involves identifying and removing redundant conditions or actions. This can be done by analyzing the conditions and actions to find any patterns or duplicates. For example, if multiple rows lead to the same action, they can be merged into one. This reduces the size and complexity of the table while preserving its decision logic.
- Consider a scenario where there are multiple rules, but some of them are contradictory (i.e., one rule suggests one action, and another suggests the opposite). How would you handle such conflicts in a decision table?
- Conflicting actions should be resolved through prioritization or clarifying business rules. If two rules conflict, one may need to be modified or removed, or an additional condition may be required to distinguish between the two cases. In some systems, a conflict resolution mechanism can be added to decide the correct action.
Practical Questions
- You are tasked with developing a decision table for a credit card approval system. The conditions and actions are as follows:
- Condition 1: Is the applicant’s annual income above $30,000? (Yes/No)
- Condition 2: Does the applicant have a good credit score? (Yes/No)
- Action 1: Approve card
- Action 2: Reject card
- Action 3: Approve with a lower credit limit
Draw the decision table and explain how you would implement it in a software system.
Decision Table:
| Condition Stub | Condition 1 (Income > $30,000) | Condition 2 (Good Credit Score) | Action Stub | Action 1 (Approve Card) | Action 2 (Reject Card) | Action 3 (Lower Credit Limit) |
|---|---|---|---|---|---|---|
| Rule 1 | Yes | Yes | Action 1 | Approve card | ||
| Rule 2 | Yes | No | Action 3 | Approve with lower credit limit | ||
| Rule 3 | No | Yes | Action 2 | Reject card | ||
| Rule 4 | No | No | Action 2 | Reject card |
Explanation:
- Rule 1: If the income is above $30,000 and the credit score is good, approve the card.
- Rule 2: If the income is above $30,000 but the credit score is not good, approve the card with a lower credit limit.
- Rule 3: If the income is below $30,000 but the credit score is good, reject the card.
- Rule 4: If neither condition is met, reject the card.
Implementation: In a software system, this decision table can be implemented using if-else conditions or a rule engine. Each row of the decision table corresponds to a decision rule that can be checked programmatically based on the applicant’s income and credit score.
True/False and Multiple-Choice Questions
- True or False: Decision tables can only handle binary (Yes/No) conditions.
- False: Decision tables can handle conditions with multiple states, not just binary values. Extended entry decision tables allow for multiple states per condition (e.g., Low, Medium, High).
- Which of the following is a correct statement about decision tables?
- A) They can only be used for decision-making in software systems.
- B) They represent complex decision logic in a systematic manner.
- C) They are only used in mathematical modeling.
- D) They have no practical application in business rule management.
- Answer: B) They represent complex decision logic in a systematic manner.
- What is the main advantage of using a decision table in business rule analysis?
- A) It simplifies complex decision-making by clearly presenting all possible conditions and actions.
- B) It provides a flowchart of the decision process.
- C) It reduces the need for testing.
- D) It replaces all manual decision-making.
- Answer: A) It simplifies complex decision-making by clearly presenting all possible conditions and actions.
Case Study Analysis
- Given a case study of a car rental service that provides discounts based on the customer’s age, membership status, and rental duration, draw a decision table to represent the discount policy, where:
- Condition 1: Is the customer a member? (Yes/No)
- Condition 2: Is the customer under 25 years old? (Yes/No)
- Condition 3: Is the rental duration more than 5 days? (Yes/No)
The actions are:
- Action 1: Apply 10% discount
- Action 2: Apply 5% discount
- Action 3: No discount
Decision Table:
| Condition Stub | Condition 1 (Member) | Condition 2 (Under 25) | Condition 3 (Duration > 5 days) | Action Stub | Action 1 (10% Discount) | Action 2 (5% Discount) | Action 3 (No Discount) |
|---|---|---|---|---|---|---|---|
| Rule 1 | Yes | Yes | Yes | Action 1 | Apply 10% discount | ||
| Rule 2 | Yes | Yes | No | Action 2 | Apply 5% discount | ||
| Rule 3 | Yes | No | Yes | Action 1 | Apply 10% discount | ||
| Rule 4 | Yes | No | No | Action 2 | Apply 5% discount | ||
| Rule 5 | No | Yes | Yes | Action 2 | Apply 5% discount | ||
| Rule 6 | No | Yes | No | Action 3 | No discount | ||
| Rule 7 | No | No | Yes | Action 2 | Apply 5% discount | ||
| Rule 8 | No | No | No | Action 3 | No discount |
Explanation:
- Rule 1: If the customer is a member, under 25 years old, and rents for more than 5 days, a 10% discount is applied.
- Rule 2: If the customer is a member, under 25 years old, but rents for 5 days or less, a 5% discount is applied.
- Rule 3: If the customer is a member, over 25 years old, and rents for more than 5 days, a 10% discount is applied.
- Rule 4: If the customer is a member, over 25 years old, and rents for 5 days or less, a 5% discount is applied.
- Rule 5: If the customer is not a member, under 25 years old, and rents for more than 5 days, a 5% discount is applied.
- Rule 6: If the customer is not a member, under 25 years old, and rents for 5 days or less, no discount is applied.
- Rule 7: If the customer is not a member, over 25 years old, and rents for more than 5 days, a 5% discount is applied.
- Rule 8: If the customer is not a member, over 25 years old, and rents for 5 days or less, no discount is applied.