I'm just surprised that it looks like the
names/descriptions are the key; what if you
repaint the BLUE cabinet in your wife MARY'S
BEDROOM red, or for that matter if you remarry and
MARY'S BEDROOM becomes LINDA'S BEDROOM?
Does the software update all occurrences
automatically, or am I misunderstanding?
m
----- Original Message -----
From: "Jay Jaeger" <cu...@charter.net>
To: <cctalk@classiccmp.org>
Sent: Friday, October 02, 2015 5:06 PM
Subject: Re: Thoughts on manual database design?
There are three columns named Location for a
reason.
There is the column Location in a table all by
itself. That is a list
of locations - not just for manuals, but,
eventually, for all of my
artifacts.
Then there is a table of Cabinets. Each Cabinet
has a single location
at any given time. But Cabinet by itself may
not be unique, so Location
comes along for the ride as part of the key for
the table of cabinets.
Manual artifacts (copies) are stored in
Cabinets. Yes, I *could* have
created a separate key for each Cabinet, and
stored that in the Manual
table and the Cabinet table (like I did to
relate Manuals to the other
tables), but that would have actually
complicated the design, so instead
I used the same concatenation which is the key
to the Cabinet table.
The database is defined such that Location is a
foreign key in Cabinet,
and the keys to Cabinet (tee hee) are a foreign
key in Manual_Artifact.
This allows the database to *guarantee* that
there is not any Manual
whose Cabinet does not exist or a Cabinet whose
Location does not exist.
It also allows the web applications to easily
populate pull down lists
without having to read through the entire
artifacts table. With a
database this small that probably doesn't matter
much, but if the table
had millions of rows it certainly would.
Type and manufacturer are handled the same way
for the same reason.
I could have made a more relationally pure
design by creating a separate
table of Artifacts and Cabinets, Cabinets and
Locations and so on. But
because each of those relationships is just one
to many and never many
to many, there was no point in my mind (purists
would probably
disagree). Not so for manuals and machines -
many manuals may apply to
a given machine, and a given manual may apply to
many machines, so that
had relation to be stored in a separate table.
Historial digression....
I have been doing database design essentially
like this from *before*
relational databases were well known and
commercially available, at
Wisconsin DOT, which developed its own database
system called File
Handler in the early 1970's, starting on an IBM
360/65 MP with 2MB of
core. It was written because the other DBMS's
at the time were either
too slow, to big or required taking too much of
the database too often
for reorganizations. (IBM's IMS, in
particular). DB2 did not yet
exist. Huge gamble management took on the
programmers that wrote it,
which paid off in millions of dollars saved in
computer capacity alone.
For a while, for performance reasons, we had a
"cheat" that could store
a one to many relation in a single column (which
we called a "repeating
group") that was done for our drivers database.
We broke them out into
separate tables when we upgraded to an Amdahl
470/V6 in 1976.
File Handler production before I started there
in 1975, I was the
primary DBA for it for about 7 years before I
moved on to other things.
It had features like row-level blank
compression, elimination of nulls
at the column level (a bitmap indicated which
columns were present), an
API which had a LALR compiler which parsed
queries (though for online
production we required them to be pre-compiled),
full (single phase)
commit with preempt detection including
redundant log and checkpoint
files in case the machine went down mid-commit
and so on. It used
techniques for indexing that would be
recognizable today. It was almost
its own OS: by the time we were done it had (in
order of development)
its own memory management ("KORMAN" aka
"Harvey"), task management and
program loading/content management ("CONMAN").
It supported the SMP
fully, though applications were usually written
to be single-threaded in
a given serially-reusable application instance -
though you could have
multiple instances of the same application
running. A man named Robert
Tomlinson wrote the query compiler, and used
some of his work on File
Handler for his advanced degree theses (at least
his PhD, for certain).
I was an EE student at the same time he was at
U. Wisconsin, though our
paths never crossed.
Florida DOT acquired the code from us in the
late 1970's, and
established it, with some assistance from
Wisconsin DOT staff, as their
motor vehicle and/or driver database system for
many years as well. I
have a copy of that instance of the code, and
have run the thing under
Hercules, just for giggles. Wisconsin DOT
retired the last vestige of
it just last year - it had a 40 year run, all
told.
JRJ
On 10/2/2015 1:38 PM, Mike Stein wrote:
Is that the way it's done these days, e.g. the
contents of the Location
field in three places, Location and Manual_Type
only containing one
field, no keys other than Manual_Key etc.?
Looks like I'll have to brush up on database
design... ;-)
m
----- Original Message ----- From: "Jay Jaeger"
<cu...@charter.net>
To: <cctalk@classiccmp.org>
Sent: Friday, October 02, 2015 11:59 AM
Subject: Re: Thoughts on manual database
design?
On 10/2/2015 12:04 AM, william degnan wrote:
Coming up with a schema that works with
multiple manufacturers is the
big
challenge.
Not sure it is that big a challenge.
Perfection is not required. Just
the ability to find stuff later. My schema
currently has manual
manufacturer - the original manufacturer of
the machine, and then each
artifact (copy of a manual) has a publisher.
Consider the case of Apollo which got bought
by HP.
For a DNxxxx machine, the machine manufacturer
is always Apollo. For a
400 or 700 series, the manufacturer is always
HP. However a given copy
of a manual may have been published by Apollo
(older) or HP (newer) -
with the very same number. The schema
supports that.
(New schema posted at
http://webpages.charter.net/thecomputercollection/misc/manualmodel.pdf
) .
JRJ
