4 the FAQ: Are Commercial DBMS Truly Relational?
From: Kenneth Downs <firstinit.lastname_at_lastnameplusfam.net>
Date: Fri, 08 Oct 2004 12:04:32 -0400
Message-ID: <hqd6kc.4go.ln_at_mercury.downsfam.net>
It said often here that no commercially available DBMS is truly relational, but I haven't seen a succinct list of reasons. What are they?
Date: Fri, 08 Oct 2004 12:04:32 -0400
Message-ID: <hqd6kc.4go.ln_at_mercury.downsfam.net>
It said often here that no commercially available DBMS is truly relational, but I haven't seen a succinct list of reasons. What are they?
One that I have gleaned from lurking is that the DBMS's allow duplicates, as in:
CREATE TABLE AnyTable (col1 char(1), col2 char(1), col3 char(1)); INSERT INTO AnyTable (col1,col2,col3) VALUES ('A','B','C'); INSERT INTO AnyTable (col1,col2,col3) VALUES ('A','B','C');
The table create specifies no constraints, and so the next two insert statements are both allowed. The objection to this seems to be that the RDM requires an implied unique constraint on all columns of all tables. Because such a constraint is not present, they are not truly relational.
Is that right?
What are some of the other objections?
We could probably have the same discussion re: Structured Query Language is not relational.
-- Kenneth Downs Use first initial plus last name at last name plus literal "fam.net" to email meReceived on Fri Oct 08 2004 - 18:04:32 CEST