sql - C. J. Date 的 "SQL and Relational Theory"中的关系理论

Question

我卡在了“SQL and Relational Theory”这本书的某一点上，它与关系属性可以采用的类型有关。问题是这样的:

There are exceptions to the rule that relational attributes can be of any type whatsoever, of which one is that if a relation R is of type T, then attributes of R cannot themselves be of type T.

为什么？是不是因为关系 R 的类型是“Relation [name]”，所以属性不能是这种类型？

Answer 1

考虑这样的事情:

create table address {
    id int,
    name varchar(20),
    details address -- the address relation has an attribute that is another of itself
}

定义 将无限递归。