// 知識節點
const nodeSchema = {
  id: 'string',
  title: 'string',
  content: 'string',
  prerequisites: ['nodeId'],
  relatedNodes: ['nodeId'],
  exercises: ['exerciseId'],
  difficulty: 'number'
};

// 練習
const exerciseSchema = {
  id: 'string',
  nodeId: 'string',
  type: 'string', // multiple_choice, open_ended, etc
  question: 'string',
  options: ['string'], // for multiple choice
  correctAnswer: 'string',
  explanation: 'string'
};

// 使用者進度
const userProgressSchema = {
  userId: 'string',
  completedNodes: ['nodeId'],
  exerciseResults: [{
    exerciseId: 'string',
    score: 'number',
    attempts: 'number'
  }],
  skills: {
    [skillName]: 'number' // 技能熟練度
  }
};