Re: database systems and organizational intelligence

From: Dawn M. Wolthuis <dwolt_at_tincat-group.com>
Date: Wed, 26 May 2004 16:58:18 -0500
Message-ID: <c933tu$63u$1_at_news.netins.net>


"Alan" <alan_at_erols.com> wrote in message news:2hkd28Fe0ou7U1_at_uni-berlin.de...
> See inline =====>>>>>
>
> "Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message
> news:c92r6d$23i$1_at_news.netins.net...
> > "Alan" <alan_at_erols.com> wrote in message
> > news:2hk09hFdml8oU1_at_uni-berlin.de...
> > > Your comment below is a joke, I hope.
> > >
> > > A functional dependency is a property of the SEMANTICS or MEANING of
the
> > > attributes. It occurs at the "business" level. It is something that
> > business
> > > people can tell you. Like (a not perfect example, but easy to
> understand):
> > > Each person in our company has a Social Security Number, and each
Social
> > > Security Number (SSN) identifies one and only one person. So, in the
> > > miniworld of our company, we know that the value of an employee's SSN
> > > uniquely determines the employee's name. Before any entities or
tables
> > are
> > > created, before any code is written. A functional dependency is a
> > constraint
> > > between two sets of attributes within the miniworld of the database
(our
> > > company).
> > >
> > > "Functional" in this context means "unique". It has nothing to do with
> > > functions as you are thinking of them.
> >
> > When you write down a functional dependency with the little arrow in it,
> > just what does that arrow mean? I was thinking it was a mapping from
one
> to
> > the other. And what's another word for a mapping? Function, perhaps?
> I've
> > never known "functional" to mean "unique" -- is that your own personal
> > definition or is there some industry use of the term in this way?
>
>
> =====>>>>> The "-->" It means "uniquely determines," which is described
> above. Or, by example:
>
> ssn --> emp_name

Perhaps a look at the def of a function in the cdt glossary might help. If I have a domain of ssn's and for each ssn, it uniquely determines the emp_name, then that would be a mapping from ssn's to emp_name and, therefore, a function on the domain of ssn's to the range of emp_names.

> > > It has zero, nothing, nada, zip to do with code. Nothing at all.
> Nothing.
> >
> > It's all code.
> > It's all data.
>
> =====>>>>> Code can be data (when stored in a database, such as the way
> Oracle stores user-defined stored procedures, but data is not code. Data
can
> be used in code, either as a variable or a constant.

If a student's GPA is never stored in the database, but all of the data required to derive the GPA are stored values, then if I query the database using a stored procedure or UDF or virtual field (by whatever name you want to call derived data) to request SELECT GPA FROM MY_VIEW; (for example), then am I requesting the GPA data from the system or not? I realize there is some terminology here and we can make various definitions, but I would suggest that I'm requesting the GPA data from the system, even though it isn't stored there. To retrieve the GPA, I need to mix data and functions on that data.

It's all data
It's all functions

--dawn Received on Wed May 26 2004 - 23:58:18 CEST

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