Separate PK in Jxn Tbl?

"James A. Fortune" wrote in message
...
David Cressey wrote:

database, is qualitatively different from the design target of the
people
who write Access databases and applications.

If they ever get to the point where the complexity of what they are
doing
matches the complexity of what practitioners using SQL Server, Oracle,
or
DB2 are doing, or the complexity that database theorists are
addressing,
they will be forced to either learn or disprove what some of us know, or
think we know.

I don't have broad enough experience to dispute your argument. I
understand that people who specialize in SQL and deal with more complex
situations than most develop practices that make use of their more
intimate knowledge of SQL. However, I can't just take their word about
their decisions. I have to understand how those choices apply to what
I'm doing.

I agree, absolutely. What I was arguing against was the dismissal without
evaluation of what theorists have to offer.



Without making light of their potential contribution, I
avoid the specious argument that because a large company or IT
department does things a certain way or spends more money on the problem
makes their solution inherently correct. Plus, the complexity of the
problems they face often argue against their use in Access. Few Access
developers have the luxury to hire or supervise a full-time SQL
developer. If using multiple field natural keys causes a problem(s), a
full-time SQL developer has time to work with the SQL until the problem
is solved. SQL is only part of our job.


SQL isn't the silver bullet, either.

Maybe many Access programmers prefer a single key to limit the number of
fields that get corrupted :-).

In that case, I believe they are wrong.

"Roy Hann" wrote in message
...
"Brian Selzer" wrote in message
news

Constraints should always be checked by the DBMS, not by applications.

I agree very heartily with the first part of this statement, for the
reasons you give below. I disagree with the second part (as stated).
There is no reason why applications shouldn't also test what constraints
they can. The problem is that they should not have hand-coded
re-implementations of the constraints because those will get out of sync
with the database over time. What would be very nice is if one day it were
possible for applications to download the relevant constraints at
run-time, the way they presently download other metda-data.


That's a good point. I should have said instead, "Constraints should always
be /enforced/ by the DBMS, not by applications." It is often a good thing
for an application to do some checking because it can reduce the number of
round-trips, and maybe even some transaction rollbacks.

If you have two separate applications that manipulate the same table, and
one enforces one constraint while another enforces another, then all you
need to do to bypass one constraint is to use the other application!
What, then, is the point of even having the constraint?

Roy

"Sylvain Lafontaine" sylvain aei ca (fill the blanks, no spam please)
wrote in message ...
In my opinion, the only sound reason for using artificial keys is when
the values of a natural key do not permanently identify individuals in
the Universe of Discourse--that is, the micro-world that the database is
supposed to be a model of--and when there is a demonstrable requirement
for permanent identification. Any other use adds complexity for
complexities sake--in other words, for no particularly good reason.

Even in the very few cases were you think that a natural key will be a
true natural key, ie. it will be permanent and totally managed at 100%
(which mean no data entry error of any kind, no change of value because of
identity theft, etc., etc.); the privacy issues will forbid their use in
many cases. Many countries now forbid by law to ask for something such as
your social security number when you don't need it and when you need it,
to use it as a key instead of storing it confidentially (ie., by
encrypting it).


So, where does it say that there can only be one natural key on a table?

Even MS had problem with this in the past: the first version of the
algorithm for generating a GUIG was using the NIC number as part of its
algorithm. They had to remove it later and now, the generation of any
GUIG is totally random. The older algorithm is still available in Windows
under another name but MS warns that anyone using it might be doing so
illegally under the laws of their countries.

The same argument apply to things like RFID: how many of you would like to
see big corporation to know which medicaments you are bringing home or
your spouse to know that you have just bought a box of condom?


Why should it be a problem for my spouse to know that I just bought a box of
condoms? More often than not she is the one who lets me know that we need
them. Oh! Wait! I get it! That must be something those of you who can't
keep it in your pants worry about.

Using natural keys is like building a castle of cards: they might look
impressive but it doesn't take to much to bring them down.


Even with artificial keys, you still need natural ones. Without them, you
can have multiple values for a key that mean exactly the same thing, but
with no way to determine which, thereby rendering the key useless.

--
Sylvain Lafontaine, ing.
MVP - Technologies Virtual-PC
E-mail: sylvain aei ca (fill the blanks, no spam please)


"Brian Selzer" wrote in message
news

"James A. Fortune" wrote in message
...
David Cressey wrote:

database, is qualitatively different from the design target of the
people
who write Access databases and applications.

If they ever get to the point where the complexity of what they are
doing
matches the complexity of what practitioners using SQL Server, Oracle,
or
DB2 are doing, or the complexity that database theorists are
addressing,
they will be forced to either learn or disprove what some of us know,
or
think we know.

I don't have broad enough experience to dispute your argument. I
understand that people who specialize in SQL and deal with more complex
situations than most develop practices that make use of their more
intimate knowledge of SQL. However, I can't just take their word about
their decisions. I have to understand how those choices apply to what
I'm doing. Without making light of their potential contribution, I
avoid the specious argument that because a large company or IT
department does things a certain way or spends more money on the problem
makes their solution inherently correct. Plus, the complexity of the
problems they face often argue against their use in Access. Few Access
developers have the luxury to hire or supervise a full-time SQL
developer. If using multiple field natural keys causes a problem(s), a
full-time SQL developer has time to work with the SQL until the problem
is solved. SQL is only part of our job.

It has been nice to see posters in microsoft.public.access such as Jamie
Collins and Ken Sheridan, who seem to have a lot of standard SQL
experience, branch off into other issues that Access programmers face. I
think their understanding of those issues can help us differentiate
between purely SQL issues and Microsoft implementation issues. We all
agree that Microsoft has made questionable design decisions in Access,
but the possibility of inclusion of unbound forms or of AutoNumber
primary keys might not be part of that list, as some have suggested. I
have enough experience to say that using unbound forms in Access and
using artificial keys did not cause any problems when scaling an Access
application up to an ASP solution using SQL Server. For something more
complicated perhaps there are subtle issues that arise that merit our
attention.

Table level constraints also raise an issue. At the table level, there
is no VBA code run to ensure that any constraints (e.g., on the natural
keys themselves) are enforced. Thus, a set of natural keys is
sufficient to specify the key constraint. Any artificial key becomes
superfluous. The possibility of separate applications using the same
table, brought up by David Fenton, brings up the interesting possibility
that the applications have separate, possibly disparate constraints. In
disparate constraint situations not all of the constraints can be at the
table level, although they can be specified at the query level in each
application rather than via code.


Constraints should always be checked by the DBMS, not by applications.
If you have two separate applications that manipulate the same table, and
one enforces one constraint while another enforces another, then all you
need to do to bypass one constraint is to use the other application!
What, then, is the point of even having the constraint?

Maybe many Access programmers prefer a single key to limit the number of
fields that get corrupted :-). Perhaps an enumeration of sticky
situations encountered by those using multiple field natural keys would
help us understand why some avoid them. Maybe better solutions to those
sticky problems would encourage developers to stay with natural keys
more often.


In my opinion, the only sound reason for using artificial keys is when
the values of a natural key do not permanently identify individuals in
the Universe of Discourse--that is, the micro-world that the database is
supposed to be a model of--and when there is a demonstrable requirement
for permanent identification. Any other use adds complexity for
complexities sake--in other words, for no particularly good reason.

James A. Fortune

Quoth Roy Hann:
What would be very nice is if one day it were possible for applications to
download the relevant constraints at run-time, the way they presently
download other metda-data.

Dataphor does this.
--
Jon

"Jon Heggland" wrote in message
...
Quoth Roy Hann:
What would be very nice is if one day it were possible for applications
to download the relevant constraints at run-time, the way they presently
download other metda-data.

Dataphor does this.

You don't think I was clever enough to come up with the idea all by myself
do you? :-)

I admire what Dataphor set out to do. But having been forced to adopt SQL
against my will a long time ago, I am under no illusion that anything better
than SQL will ever catch on. The best hope is that embedded SQL might be
less stupid in future.

Roy

Quoth Roy Hann:
"Jon Heggland" wrote in message
...
Quoth Roy Hann:
What would be very nice is if one day it were possible for applications
to download the relevant constraints at run-time, the way they presently
download other metda-data.
Dataphor does this.

You don't think I was clever enough to come up with the idea all by myself
do you? :-)

Why not? It's a pretty simple idea, really.

I admire what Dataphor set out to do. But having been forced to adopt SQL
against my will a long time ago, I am under no illusion that anything better
than SQL will ever catch on.

Well, Dataphor databases are typically built on top of SQL databases.
Just tell management that Dataphor is really just a presentation layer
on top of SQL.

The best hope is that embedded SQL might be less stupid in future.

If that was my best hope, i think I would quit being a database engineer.
--
Jon

"Jon Heggland" wrote in message
...
Quoth Roy Hann:
The best hope is that embedded SQL might be less stupid in future.

If that was my best hope, i think I would quit being a database engineer.

I admire your optimism. Can we agree to meet again in this very place 20
years from now to discuss how it went? :-)

Roy

"Brian Selzer" wrote in message
news

"Roy Hann" wrote in message
...
"Brian Selzer" wrote in message
news

Constraints should always be checked by the DBMS, not by applications.

I agree very heartily with the first part of this statement, for the
reasons you give below. I disagree with the second part (as stated).
There is no reason why applications shouldn't also test what constraints
they can. The problem is that they should not have hand-coded
re-implementations of the constraints because those will get out of sync
with the database over time. What would be very nice is if one day it
were
possible for applications to download the relevant constraints at
run-time, the way they presently download other metda-data.


That's a good point. I should have said instead, "Constraints should
always
be /enforced/ by the DBMS, not by applications." It is often a good thing
for an application to do some checking because it can reduce the number of
round-trips, and maybe even some transaction rollbacks.

I think that if an application does some checking, it will also do some
enforcing.

I think you might have been aiming at something like the following:

The DBMS should always enforce the constraints that it can enforce, rather
than relying on applications to refrain from writing data that violates the
constraints.

Note that the above is silent on what applications should or should not do
regarding constraints.

-CELKO- wrote:

Thank you. You made my point. I was only wrong on the non-English
speaking programmers. It doesn't appear to be a famous failure, more
like a internal problem exacerbated by management.

It is a good classic screw up, with blame for everyone!

1) ACCESS programmer builds desktop app on his own that looks good for
his immediate needs.

Obviously a dedicated person that takes some initiative.

2) Management sees the app and wants to deploy it all over the
company. Hey, why design anything new when we have it already?

Dilbert's pointy headed boss comes to the rescue.

3) ACCESS programmer claims it will deploy and and management believes
him.

The programmer is correct.

4) It does not scale, it does not interface with mainframe apps,
external apps, etc. It has no documentation, etc.

Management decides unwisely to not spend money to upgrade it or redefine
it to meet goals. Programmer has a life and a job and doesn't have time
to write documentation. Mgt is too cheap to provide him with a
technical writer or someone to do bug testing. This is obviously not an
important project.

5) ACCESS programmer now has a career being the only guy who can keep
the sinking boat up. Never mind how many times a week it has to be re-
booted or how much data is lost.

Programmer skill level may come into play. Feature creep may come into
play. Management thought on project is nil. Something for nothing and
the chicks for free.

6) Neither the programmer nor management will scream for help and ask
for a budget. Management would look stupid; programmer would lose his
job and power

You get what you pay for.

I can't fault the programmer. He made something to make his job easier.
Mgt glommed onto it but wasn't willing to invest in it.

I asked before, are you on the committee that oversees the project? If
so, look in the mirror.

"David Cressey" wrote in message
news:wOFoj.5442$4f.4907@trndny06...

"Brian Selzer" wrote in message
news

"Roy Hann" wrote in message
...
"Brian Selzer" wrote in message
news
Constraints should always be checked by the DBMS, not by applications.

I agree very heartily with the first part of this statement, for the
reasons you give below. I disagree with the second part (as stated).
There is no reason why applications shouldn't also test what
constraints
they can. The problem is that they should not have hand-coded
re-implementations of the constraints because those will get out of
sync
with the database over time. What would be very nice is if one day it
were
possible for applications to download the relevant constraints at
run-time, the way they presently download other metda-data.


That's a good point. I should have said instead, "Constraints should
always
be /enforced/ by the DBMS, not by applications." It is often a good
thing
for an application to do some checking because it can reduce the number
of
round-trips, and maybe even some transaction rollbacks.

I think that if an application does some checking, it will also do some
enforcing.

I think you might have been aiming at something like the following:

The DBMS should always enforce the constraints that it can enforce, rather
than relying on applications to refrain from writing data that violates
the
constraints.

Note that the above is silent on what applications should or should not do
regarding constraints.


Yes.