《北史·列传·卷三十》
郑玄注释说：在内城则聘请老师担任抚养和教育的任务，为了使公卿大臣的子弟能得以学习；外城则设有太学，配有负责教育的官员。
郑氏注： 内则设师保以教，使国子学焉；外则有太学庠序之官。 
Zheng Xuan's commentary states: In the inner city, teachers were engaged for the purpose of nurturing and educating the young, in order that the sons of the dukes and ministers might have an opportunity to learn; in the outer city there was the Imperial University, staffed by officials in charge of education.