Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!dptg!ulysses!andante!alice!debra
From: debra@alice.UUCP (Paul De Bra)
Newsgroups: comp.databases
Subject: Re: Ingres and referential integrities
Keywords: Ingres referential integrities
Message-ID: <9677@alice.UUCP>
Date: 25 Jul 89 13:59:58 GMT
References: <3081@rti.UUCP> <3225@rtech.rtech.com>
Reply-To: debra@alice.UUCP ()
Distribution: comp
Organization: AT&T, Bell Labs
Lines: 52

In article <3225@rtech.rtech.com> robf@squid.UUCP (Robert Fair) writes:
}Lynn writes:
}>I'm curious as to why Ingres doesn't provide referential integrities.
}>I'm aware that you can build in referential constraints through QBF
}>and VIFRED but not as part of the data definition. Does anyone know
}>why Ingres chose not to provide this part of the relational model?
}>
}>Thanks,
}>Lynn
}
}If you mean single-table constraints, INGRES has  had them for many
}years, for example:
}
}	CREATE INTEGRITY ON employee IS age>15 AND  age<75;
}
}will enforce the integrity that all employees are between 15 and 75.
}
}Starting with release 6, multi-table update integrity can be enforced by
}using database procedures, typically linked updates are coded using
}dbprocs similar to:
}
} [example procedure deleted]
}
}Robert Fair
}Relational Technology 
}Technical Support.

Well, it doesn't look good if RTI's technical support doesn't even know
what referential integrity means, does it?

Now, as far as i know, it means the following:
given for instance 2 relations:
EMP (EMPNO, DNO)      employees with their department
DEPT(DNO, MANAGER)    departments with their manager

Then referential integrity (given EMPNO is a key in EMP and DNO a key in
DEPT) would imply that EMP cannot contain a DNO which does not occur in
DEPT.

There should be no need for procedures or other low-level tricks to
enforce this constraint.

In a hierarchical database the link between the DNO's in EMP and in DEPT
would come natural, and referential integrity is therefore easy.
In a relational database there is no automatic link between the two
DNO's which makes it harder to implement referential integrity.

Paul.
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