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From:Martijn Tonies Date:October 29 2003 7:31am
Subject:Re: Is MySQL Relational? (was: Foreigner keys in MySQL?)
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Hi,

> For decades, people have debated in comp.databases.theory and elsewhere
how
> a 'relational database' should be defined.
>
> Codd's original 1970 paper sketches the relational algebra as a query
> language of a relational database, though Codd is not very precise about
> what the query language exactly should be. The paper also mentions
integrity
> constraints. Relations in the 1970 paper are defined as mathematical sets,
> that is, no duplicate rows in tables or any query results are allowed.
>
> Thus, no SQL database is Codd-1970-relational, because SQL allows
duplicate
> rows.
>
> Codd's 12 rules, from about 1987, demand that a 'relational database' must
> satisfy several strict conditions. For example, any view 'theoretically
> updateable should be updateable with the data manipulation language'.

Mainly because "views" and "tables" are pretty much the same in the theory.

> No existing database is even close to being Codd-12-relational.

Indeed.

> On the other hand, for example, Elmasri and Navathe in their university
> textbook define a 'relational database' less strictly, and mention
Microsoft
> Access and Oracle as examples of an 'RDBMS'.
>
> Thus, MySQL apparently is Elmasri-Navathe-relational, but not
> Codd-1970-relational. The same holds for DB2, Oracle, and MS SQL Server.

I guess it also comes down to what you're used to work with. If you're used
to using domains, check constraints etc, you might consider any database
engine that doesn't have these, a "lesser" database engine.

Luckily - as said before - things are improving.


With regards,

Martijn Tonies
Database Workbench - developer tool for InterBase, Firebird & MS SQL Server.
Upscene Productions
http://www.upscene.com

Thread
Foreigner keys in MySQL?Juliana Gubert Ehrensperger28 Oct
  • RE: Foreigner keys in MySQL?Michael McTernan28 Oct
  • Re: Foreigner keys in MySQL?Peter Brawley28 Oct
  • Re: Foreigner keys in MySQL?bluejack28 Oct
    • Re: Foreigner keys in MySQL?Martijn Tonies28 Oct
      • Is MySQL Relational? (was: Foreigner keys in MySQL?)bluejack28 Oct
        • Re: Is MySQL Relational? (was: Foreigner keys in MySQL?)Martijn Tonies28 Oct
      • Re: Foreigner keys in MySQL?shrek-m@gmx.de28 Oct
RE: Foreigner keys in MySQL?John Griffin28 Oct
Re: Is MySQL Relational? (was: Foreigner keys in MySQL?)jeffrey_n_Dyke28 Oct
  • Re: Is MySQL Relational? (was: Foreigner keys in MySQL?)Saqib Ali28 Oct
RE: Is MySQL Relational? (was: Foreigner keys in MySQL?)Saqib Ali28 Oct
Re: Is MySQL Relational? (was: Foreigner keys in MySQL?)bluejack28 Oct
Re: Is MySQL Relational? (was: Foreigner keys in MySQL?)Heikki Tuuri28 Oct
  • RE: Is MySQL Relational? (was: Foreigner keys in MySQL?)Mike Brando28 Oct
    • Re: Is MySQL Relational? (was: Foreigner keys in MySQL?)Martijn Tonies29 Oct
Re: Is MySQL Relational? (was: Foreigner keys in MySQL?)Peter Brawley28 Oct
Re: Is MySQL Relational? (was: Foreigner keys in MySQL?)Martijn Tonies29 Oct