Database design for a template based evaluation system - sql

Question

We are working on a database to store some evaluations we conduct. There are a few different types of evaluations and some have changed over time. Because of this we need to keep a record of exactly what an evaluation looked like when it was undertaken.
I figured that the best way to support this would be through a template style system.
With:
A table saving all possible options;
A table mapping options to a template;
An evaluations table mapping a participant to a template on a date/time; and
A table mapping evaluator comments to an option of an evaluation.
This is a skeleton for the design:
CREATE TABLE options (
id SERIAL PRIMARY KEY,
option TEXT NOT NULL
);
CREATE TABLE templates (
id SERIAL PRIMARY KEY,
name TEXT NOT NULL
);
CREATE TABLE template_options (
template INTEGER NOT NULL REFERENCES templates( id ),
option INTEGER NOT NULL REFERENCES options( id ),
UNIQUE ( template, option )
);
CREATE TABLE participants (
id SERIAL PRIMARY KEY,
name TEXT NOT NULL
);
CREATE TABLE evaluations (
id SERIAL PRIMARY KEY,
template INTEGER NOT NULL REFERENCES templates( id ),
participant INTEGER NOT NULL REFERENCES participants( id ),
date TIMESTAMP WITH TIME ZONE NOT NULL
);
CREATE TABLE evaluation_data (
template INTEGER NOT NULL REFERENCES templates( id ),
option INTEGER NOT NULL REFERENCES options( id ),
evaluator_comments TEXT NOT NULL,
);
The design is able to capture our data but doesn't restrict the options saved in evaluation_data to the subset specified in the evaluation's template's option mapping. We could probably enforce it with a trigger (we can definitely do it with application logic [we are doing so at the moment]) but are we going down the wrong path with this design?
Can anybody think of a better way to do it?
Edit:
Added an example of a potential trigger we would need to use to ensure valid options are enforced with this design.
CREATE FUNCTION valid_option() RETURNS trigger as $valid_option$
BEGIN
IF NOT NEW.option IN ( SELECT template_options.option
FROM template_options
INNER JOIN templates
ON template_options.template = templates.id
WHERE templates.id = ( SELECT evaluations.template
FROM evaluations
WHERE evaluations.id = NEW.evaluation ) ) THEN
RAISE EXCEPTION 'This option is not mapped for this evaluations template.';
END IF;
RETURN NEW;
END
$valid_option$ LANGUAGE plpgsql;
CREATE TRIGGER valid_option BEFORE INSERT ON evaluation_data FOR EACH ROW EXECUTE PROCEDURE valid_option();

Answer 1

Remember that you need two sets of tables. The first set containing the assessment, questions, answer alternatives, categories(?) needed to display the assessment to the participant. The second set of tables to record data about the evaluation (ie. the participant taking the assessment): which assessment, which questions, which answer alternatives and in which order they were presented, which answer they entered (are they allowed to answer the same question multiple times?), etc.
We're using the following structure (I've removed topic scoring since you didn't ask about it):
Models for presenting an assessment:
Assessment: assessment_name, passing_status, version
Question: assessment, question_number, question_type, question_text
AnswerAlternative: question, correct?, answer_text, points
Models for recording an evaluation (participant taking an assessment):
Progress: started_timestamp, finished_timestamp, last_activity, status (includes "finished")
Result: user, assessment, progress, currently_active, score, passing_grade?
Answer: result, question, selected_answer_alternative, answer_text, score
To achieve your goal, I would augment this by writing the generated evaluation to a table and pointing to it from Reault. You could also record the selection and presentation criteria so you can re-generate the assessment programmatically (ie. if you're selecting the questions from a larger question db and re-ordering the answer alternatives before presenting them to the participant).