The job of a relational DBMS (was: Sql request)

From: Ben Finney <>
Date: Tue, 01 Dec 2009 08:50:34 +1100
Message-ID: <>

joel garry <> writes:

> On Nov 27, 3:12 pm, Ben Finney <>
> wrote:
> > and then use a function or user application to process the relation
> > into whatever output text you like for the report. Turning relations
> > into reports isn't the job of the DBMS.
> So what is the job of the DBMS?

The job of a relational DBMS is to implement the relational model, by implementing a logical set of rlations in a physical database implementation, and to provide an interface to applications for managing and querying the relations in that database. The output of those operations should be either status messages or new relations.

> From wikipedia (just 'cause it was the first thing that popped up in
> google, you are welcome to cite others):

I'm paraphrasing my understanding of the writings of E. F. Codd, C. J. Date, and Hugh Darwen.

> "A Database Management System (DBMS) is a set of computer programs
> that controls the creation, maintenance, and the use of the database
> with computer as a platform or of an organization and its end users."

That seems fair, since it's not restricted to relational DBMS. I wasn't specific before about the fact that we're talking about *relational* database management systems behaviour, but I believe that's been the topic consistently through this thread.

> Turning relations into reports may or may not be the job of the
> database

It's not; the job of the database is to be an implementation of a data model. As you imply by making the distinction, DBMS ≠ database.

> but by definition it quite well can be the job of the Database
> Management System.

Not the relational DBMS. A DBMS might do *more* than the job of a relational DBMS, but the distinction I'm making is that one should not expect to find that behaviour in a relational DBMS since that's not its job.

> There are some things apps may do better, and some things the DBMS may
> do better. Which things may be debatable, but saying either should do
> all or neither is wrong.

The output of a query into a relational DBMS should always be a relation (or a status message). It's up to the application to use non-relational means to turn that relation into whatever other form it requires.

> Can't a function be part of the DBMS?

A non-relational function shouldn't be part of a relational DBMS, no. An application can *store* its non-relational functions in the *database*, of course, and access them there; but database ≠ DBMS.

 \          “Those who write software only for pay should go hurt some |
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_o__)                                                                  |
Ben Finney
Received on Mon Nov 30 2009 - 15:50:34 CST

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