Sheen
发表于 2009-2-5 19:50
不会把，真的是这样子的阿
menubada
发表于 2009-2-5 19:50
哈哈哈哈哈哈哈哈哈哈哈哈哈
garaa
发表于 2009-2-5 19:51
了解了，签到:)
woniuxu
发表于 2009-2-5 19:51
谢谢，签到哈
menubada
发表于 2009-2-5 19:51
oh,yeah,how are uniqueness constraints implemented in a typical object-oriented language?
wangkai057
发表于 2009-2-5 19:51
wo lai le,haha!!
menubada
发表于 2009-2-5 19:53
Usually the identification scheme would be responsible for checking the format of the strings used by its identifiers.
menubada
发表于 2009-2-5 19:53
Usually the identification scheme would be responsible for checking the format of the strings used by its identifiers.
menubada
发表于 2009-2-5 19:58
The second part of a uniqueness constraint states that an objects's identifier cannot be changed.This implies that,within a scheme, the same string cannot be switched from one object to another.This can be enforced by ensuring that identifiers cannot be deleted and that the mappings from the identifier are immutable--that is ,they are assigned for good.In reality some schemes do recycle identifiers,but only identifiers that have never been used can be recycled.
menubada
发表于 2009-2-5 19:59
The second part of a uniqueness constraint states that an objects's identifier cannot be changed.This implies that,within a scheme, the same string cannot be switched from one object to another.This can be enforced by ensuring that identifiers cannot be deleted and that the mappings from the identifier are immutable--that is ,they are assigned for good.In reality some schemes do recycle identifiers,but only identifiers that have never been used can be recycled.