Re: database systems and organizational intelligence
Date: Thu, 27 May 2004 03:45:16 GMT
Message-ID: <gvdtc.22728$4%3.3430_at_nwrdny01.gnilink.net>
Top-posting - please don't shoot me.
The definitions, examples, and explanations I've given of functional
dependency are either quoted directly or paraphrased slightly from
"Fundamentals of Database Systems" 3rd Ed. by Elmasri & Navathe. This text
is used in Masters programs at major universities.
GPA as you have described is an example of "derived" data. It is based on data already stored. Of course code and functions (which are just pre-written chunks of code) are needed to extract data, but that does not mean that code and data are the same thing. You are essentially saying that driving a car and directions to a destination are the same thing. Directions are data (information, actually), driving is code (specific actions taken to affect a certain result). They are two different things.
Or, try this (wish I had thought of this sooner)... data:noun/code:verb, or more accurately, data:subject/code:predicate.
The cdt glossary was written by whom? They have what credentials?
Lather, rinse, repeat.
"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message
news: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 Thu May 27 2004 - 05:45:16 CEST