Rational XDE,有关数据库建模中non-identity和identity关系的区别？

[heavenkiller]

有什么区别呢？生成的代码都是一样的。
CREATE TABLE User (
ID SMALLINT IDENTITY NOT NULL,
Name VARCHAR ( 100 ) NOT NULL
)
GO

CREATE TABLE Channel (
ID SMALLINT IDENTITY NOT NULL,
ChannelName SMALLINT NOT NULL,
InChargeUser SMALLINT NOT NULL
)
GO

ALTER TABLE User
ADD CONSTRAINT Use_Constraint3 UNIQUE NONCLUSTERED (
ID
)
GO

ALTER TABLE User
ADD CONSTRAINT Use_Constraint4 PRIMARY KEY NONCLUSTERED (
ID
)
GO

ALTER TABLE Channel
ADD CONSTRAINT Cha_Constraint2 PRIMARY KEY NONCLUSTERED (
InChargeUser,
ID
)
GO

ALTER TABLE Channel
ADD CONSTRAINT Cha_Constraint1 UNIQUE NONCLUSTERED (
ID
)
GO

ALTER TABLE Channel
ADD CONSTRAINT Cha_Constraint3 FOREIGN KEY (
InChargeUser
)
REFERENCES User (
ID
)
ON DELETE CASCADE
GO


在处键约束上都是
ALTER TABLE Channel
ADD CONSTRAINT Cha_Constraint3 FOREIGN KEY (
InChargeUser
)
REFERENCES User (
ID
)
ON DELETE CASCADE
GO
两者的意义是不同的，但是为什么实现是一样的呢？
我用的是Rational XDE，请高手指教!