对借书中常见的续借现象进行分析，续借可以延长持有书籍的时间，但存在续借之前被其他读者预约而使续借失效的可能性。
Renewing can extend the holding duration of the book, but is invalid if there is an order in advance from other readers before the renewing.
如果一个出版商可以通过这种方式“持有”多本书籍，就称之为一对多关系。
If one publisher can "have" multiple books in this way, it's called a one-to-many relation.
如果一个出版商可以通过这种方式“持有”多本书籍，就称之为一对多关系。
If one publisher can "have" multiple books in this way, it's called a one-to-many relation.
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