Dear Simon,
I wish I could point you to a good book. C.J. Date is a good author,
but I don't know for beginners.
On the web, you could start at
http://www.aisintl.com/case/datamdl.html
This will give you some background, tho it's really meant for data
modellers & covers some theoretical distinctions whose subleties
escape everyone else....
Check their nice bibliography. Relational stuff is basically the same
as in 1970. http://www.aisintl.com/case/biblio.html
Access help doesn't cover any methodological foundations.
It's really not too hard, and this site is small & logical, if
subtle.
And a primary key? Relational data is organised in rows of values for
what you're interested in, e.g. images. Every row has a value or
place marker for a "column" or data field, e.g. "frame number" or
"subject".
The primary key for an image could be "Roll number, frame number"
If you have the roll number and frame number, you've identified the
image, assuming you assign roll numbers uniquely.
You could make up keys, like image-ID and assign a value to each
image and look it up by that.
If you've tracked the exact date, time & place, that probably
uniquely identifies the image.
Your choice, depending on your judgement of what's simplest, least
likely to change, shortest, and most available.
The primary key of one table is used by other tables to look up the
rows in the first table. In the second table, the primary key of the
the first table is stored & called a "foreign key"
See also:
www.lebow.drexel.edu/Gefen/mis632week4.pdf
and
mis.bus.sfu.ca/bus362/pdf/362-2000-3-L08.pdf
You design a DB by deciding what you're interested in (data),
identifying all the interdependencies, and separating the data out
into tables where each field that isn't part of the primary key is
completely "determined" by the value of the primary key, the whole
key, and nothing but the key.
This process is called "Normalization"
Tom
On 7 Feb 2001, at 22:39, sayeth Simon Evans <sje@xxxxxxxxxxxxxxxxxx>
> Hello Tom,
>
> I was intrigued by your post. My knowledge of databases is very limited. I'm
> trying to suss out primary keys. I have heard of them at work, but how would
> you use them across tables in this context? Perhaps I'd better get a book on
> databases.
>
> Any (straightforward) enlightenment would be appreciated. I'm a computer
> tech but only tend to learn as I need stuff. Looks like I need to understand
> databases...
>
> Thanks,
>
> Simon E.
>
-----------------------------------(no spam please)
Tom Trottier <TomATrottier@ home.com> ICQ: 57647974
Abacurial Information Technology Consulting
400 Slater St. Suite 415, Ottawa ON Canada K1R 7S7
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