队列和主题域的这一统一非常重要，有必要进行深入的研究。
This unification of the queue and topic domains is significant and deserves a closer look.
Alpha rule：对象的域集是主题域集的一个子集。
Alpha rule - Object's domain set is a subset of subject's domain set.
每当用户尝试通过主题访问对象时，此内核会在赋予对此对象的访问权限之前先验证这些主题域。
Whenever users try to access an object through subject, the kernel verifies the subject domains before granting access to an object.
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