How Can a Database Schema Effectively Handle Conditional Questions in a Survey System?

Database Schema for Conditional Questions in a Survey System

The provided database schema, consisting of tables for Survey, Question, Answer, and PossibleAnswers, addresses the need for a simple survey system. However, to incorporate conditional questions, additional considerations are required.

Introducing Conditional Logic

The key to supporting conditional questions lies in linking the dataset to identify the relationships between questions and their respective answers. An additional table, QuestionDependency, can be introduced to define these dependencies.

QuestionDependency Table

The QuestionDependency table establishes the prerequisites for displaying certain questions. It includes the following columns:

• DependentQuestionID: ID of the question that is dependent on a previous answer.
• PrerequisiteQuestionID: ID of the question whose answer triggers the display of the dependent question.
• PrerequisiteAnswerID: ID of the specific answer to the prerequisite question that determines whether the dependent question is shown.

Example:

Consider the example where the question "What's your favourite cigarette brand?" (Question B) should only be displayed to individuals who answered "Yes" to "Do you buy cigarettes?" (Question A). The QuestionDependency table would have the following entry:

DependentQuestionID	PrerequisiteQuestionID	PrerequisiteAnswerID
2	1	1

Database Queries for Conditional Logic

To implement the conditional logic, the survey system would need to query the QuestionDependency table to determine which questions should be displayed based on the user's previous answers. This can be achieved using queries such as:

SELECT QuestionID
FROM Question
WHERE QuestionID NOT IN (
    SELECT DependentQuestionID
    FROM QuestionDependency
    WHERE PrerequisiteQuestionID = 1 AND PrerequisiteAnswerID = 2
)

This query would return a list of question IDs for questions that should be hidden from users who answered "No" to question A.

By incorporating the QuestionDependency table and implementing appropriate database queries, the proposed schema provides a flexible and effective way to support conditional questions in a survey system.

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