[4.2.1功能分类](4.2.1%E5%8A%9F%E8%83%BD%E5%88%86%E7%B1%BB.md) [4.2.2应用分类](4.2.2%E5%BA%94%E7%94%A8%E5%88%86%E7%B1%BB.md) [4.2.3既按功能分类又按应用分类](4.2.3%E6%97%A2%E6%8C%89%E5%8A%9F%E8%83%BD%E5%88%86%E7%B1%BB%E5%8F%88%E6%8C%89%E5%BA%94%E7%94%A8%E5%88%86%E7%B1%BB.md) [4.2.4特殊情况](4.2.4%E7%89%B9%E6%AE%8A%E6%83%85%E5%86%B5.md)