# Bayes network - independence of nodes

Let's say that the Bayes network consists of node K that represents knowledge. Since knowledge is evaluated using questions, each question is represented by the node related to the knowledge node (Q1, Q2). Regarding the types of questions, let's say there are inverse questions that are supposed to be related and form a cycle.

If it is ensured in the testing process that specific inverse question (e.g. Q2) is never asked if the corresponding question (e.g. Q1) is not answered correctly, is it allowed to drop one relation (Q2->Q1) and solve the cycle problem?

Bayesian networks need to be acyclic. You don't put an arrow on every related node. Because, it is always the case that if $$X$$ is related to $$Y$$, $$Y$$ is related to $$X$$. Otherwise it'd be an undirected graph, or a directed graph with every relation doubled. Conceptually, causal relations make more sense when building the graph. And, the builder of the graph makes assumptions. If the resulting graph violates the acyclic property, then Bayesian Networks might not be a good framework to solve the problem.
For your case, I think the following sentence describes $$P(Q_2|Q_1=0)=0$$ which is a causal dependence and maybe encoded as an arrow from $$Q_1$$ to $$Q_2$$, and the inverse one can be dropped.