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Next: An encouraging note to hopeless DBA's
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External
Since: May 29, 2008
Posts: 7
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(Msg. 1) Posted: Thu May 29, 2008 2:30 pm
Post subject: Multiple tables refer to one -To use foreign keys or not?
Archived from groups: comp>databases>theory (more info?)
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As one of my first encounters with SQL (The RDBMS used is MySQL 5.1),
my colleague and I have designed the following (it's a part of a
catalog system for a museum):
We have an "attachments" table, which can refer to "works_of_art",
"people", "reproductions" (Let's say, more than three tables). So a
work of art can have attachments, a person can have a different
attachment, etc.
To be able to relate each object to its eventual attachments, one
solution I imagined is to put N foreign keys from each of the tables
referred in attachments (if my use of the verb refer is incorrect,
please do point it out). Let's say that, for now, there are no fields
exclusive to any of the referred tables, so creating different
attachment tables is not the best obvious choice.
The alternative solution we came up with was to use two fields in
"attachments" to identify the relations: one with the id of the
referred table, and one with the "type". So 'works of art' would be 0,
'people' would be 1... The reasoning behind the decision was that my
colleague felt that too many fields would remain empty with the first
solution, and that adding a new type of "attachee" was simpler/more
efficient than adding a new foreign key.
This solution doesn't strike me as the best. We want to use cakephp to
build the app that will use the database, and while this solution
would eventually work with some manual labour, I feel it grates
against it when the rest of the design does not. Since my knowledge of
SQL is tenuous at best, I wanted to listen to some informed opinions
about this before arguing again.
By all means, if this is a WTF, point it out, the reason, and possibly
an alternative.
Saludos,
Adriano |
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External
Since: May 29, 2008
Posts: 7
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(Msg. 2) Posted: Thu May 29, 2008 4:38 pm
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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External
Since: Oct 31, 2006
Posts: 177
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(Msg. 3) Posted: Thu May 29, 2008 5:37 pm
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Adriano Varoli Piazza wrote:
>On 29 mayo, 18:38, Bob Badour wrote:
>> I will cite Date's _Principle of Incoherence_ and ask whether you are
>> re-inventing EAV, yet again?
>
>Reading http://en.wikipedia.org/wiki/Entity-Attribute-Value_model ,
>but this doesn't look like the same problem at first glance. I'll try
>to wrap my head around the concept.
>Though it does seem to be an awful lot of work for this particular
>task.
>
>Thanks for the readup anyway, if it's the right solution, good, and if
>it's not, I'll avoid reinventing stuff in the future.
It is not the right solution. It is a hideous way to do it.
Sincerely,
Gene Wirchenko
Computerese Irregular Verb Conjugation:
I have preferences.
You have biases.
He/She has prejudices. >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: Jan 15, 2008
Posts: 1017
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(Msg. 4) Posted: Thu May 29, 2008 6:38 pm
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Adriano Varoli Piazza wrote:
> As one of my first encounters with SQL (The RDBMS used is MySQL 5.1),
> my colleague and I have designed the following (it's a part of a
> catalog system for a museum):
> We have an "attachments" table, which can refer to "works_of_art",
> "people", "reproductions" (Let's say, more than three tables). So a
> work of art can have attachments, a person can have a different
> attachment, etc.
>
> To be able to relate each object to its eventual attachments, one
> solution I imagined is to put N foreign keys from each of the tables
> referred in attachments (if my use of the verb refer is incorrect,
> please do point it out). Let's say that, for now, there are no fields
> exclusive to any of the referred tables, so creating different
> attachment tables is not the best obvious choice.
>
> The alternative solution we came up with was to use two fields in
> "attachments" to identify the relations: one with the id of the
> referred table, and one with the "type". So 'works of art' would be 0,
> 'people' would be 1... The reasoning behind the decision was that my
> colleague felt that too many fields would remain empty with the first
> solution, and that adding a new type of "attachee" was simpler/more
> efficient than adding a new foreign key.
>
> This solution doesn't strike me as the best. We want to use cakephp to
> build the app that will use the database, and while this solution
> would eventually work with some manual labour, I feel it grates
> against it when the rest of the design does not. Since my knowledge of
> SQL is tenuous at best, I wanted to listen to some informed opinions
> about this before arguing again.
>
> By all means, if this is a WTF, point it out, the reason, and possibly
> an alternative.
>
> Saludos,
> Adriano
I will cite Date's _Principle of Incoherence_ and ask whether you are
re-inventing EAV, yet again? >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: Jan 15, 2008
Posts: 1017
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(Msg. 5) Posted: Thu May 29, 2008 10:11 pm
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Gene Wirchenko wrote:
> Adriano Varoli Piazza wrote:
>
>
>>On 29 mayo, 18:38, Bob Badour wrote:
>>
>>>I will cite Date's _Principle of Incoherence_ and ask whether you are
>>>re-inventing EAV, yet again?
>>
>>Reading http://en.wikipedia.org/wiki/Entity-Attribute-Value_model ,
>>but this doesn't look like the same problem at first glance. I'll try
>>to wrap my head around the concept.
>>Though it does seem to be an awful lot of work for this particular
>>task.
>>
>>Thanks for the readup anyway, if it's the right solution, good, and if
>>it's not, I'll avoid reinventing stuff in the future.
>
> It is not the right solution. It is a hideous way to do it.
And I want to make clear I wasn't accusing the OP of anything hideous. I
could not make enough sense of his post to tell what he was doing, and
some of it seemed suggestive of yet another reinvention of EAV. Not
enough to say for sure, though. >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: May 29, 2008
Posts: 7
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(Msg. 6) Posted: Fri May 30, 2008 3:29 am
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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On 30 mayo, 06:11, "Roy Hann" wrote:
> "Adriano Varoli Piazza" wrote in messagenews:1ff6aed6-4173-4f05-a723-96a3a9228344@z72g2000hsb.googlegroups.com...
> If I understand your intention correctly then I am sorry to say it probably
> is a WTF. I say "probably" because you actually describe two intentions..
> In one place you talk about relating objects (sic) to attachments, and
> immediately after that you talk about doing the opposite.
My bad. Attachments belong to objects, not otherwise (at least, not in
this design).
> I suspect you are uncomfortable with the idea of multiple attachment tables
> because superficially they would look the same (in the sense they'd have the
> same column names, each of the same type). That is a programmer's point of
> view. To a database designer they should appear to be VERY different and I
> suspect that if you look deep into the logic of what one is justified in
> doing with attachments for people versus attachments for works_of_art, those
> differences will become apparent. Once you see that you will be perfectly
> happy to have multiple attachment tables. The physical model would
> correspond closely to the logical model.
This is a _very_ useful and enlightening answer. Yet again, by your
words below...
> That makes life easy because it makes it hard to write a correctly formed
> query that executes correctly and yet gives a wrong or meaningless answer.
> Database design is not about making it easy to do correct things so much as
> it is about making it hard to inadvertently do wrong things, and rather
> paradoxically (it seems to me) that often ends up making correct things easy
> into the bargain.
>
> Having offered an opinion, I ought to say you'd be unwise to follow any
> specific advise you get from a newsgroup. We all have our own enthusiasms,
> prejudices, and preconceptions of what you are trying to do.
I'm trying to inform myself, and I have to do it on the run (i.e. not
enough time to do it right and study SQL properly, plenty to do it
over  ).
So I'll take my chances. Of course, I do try to think before I
implement anything.
Thanks.
Adriano >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: May 29, 2008
Posts: 7
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(Msg. 7) Posted: Fri May 30, 2008 3:33 am
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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On 29 mayo, 22:11, Bob Badour wrote:
> Gene Wirchenko wrote:
> > Adriano Varoli Piazza wrote:
>
> >>On 29 mayo, 18:38, Bob Badour wrote:
>
> >>>I will cite Date's _Principle of Incoherence_ and ask whether you are
> >>>re-inventing EAV, yet again?
>
> >>Readinghttp://en.wikipedia.org/wiki/Entity-Attribute-Value_model,
> >>but this doesn't look like the same problem at first glance. I'll try
> >>to wrap my head around the concept.
> >>Though it does seem to be an awful lot of work for this particular
> >>task.
>
> >>Thanks for the readup anyway, if it's the right solution, good, and if
> >>it's not, I'll avoid reinventing stuff in the future.
>
> > It is not the right solution. It is a hideous way to do it..
>
> And I want to make clear I wasn't accusing the OP of anything hideous. I
> could not make enough sense of his post to tell what he was doing, and
> some of it seemed suggestive of yet another reinvention of EAV. Not
> enough to say for sure, though.
A simple "Your post is very confusing, please clarify X, Y and Z"
would have been better.
Still, I'm not offended by people telling me I'm doing things the
worst way, or telling me what I wrote is confusing.
I half suspect it anyway. This is very new to me.
As I said, EAV is an interesting concept, and one I'd rather know, so
thanks for pointing it out, even if it's not related to this.
Saludos
Adriano >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: Oct 31, 2006
Posts: 177
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(Msg. 8) Posted: Fri May 30, 2008 10:04 am
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Adriano Varoli Piazza wrote:
[snip]
>A simple "Your post is very confusing, please clarify X, Y and Z"
>would have been better.
A clear post in the first place would be even better. I have
things to do with my time. If my first impression of a post is that I
can not easily understand it, why should I bother with it?
>Still, I'm not offended by people telling me I'm doing things the
>worst way, or telling me what I wrote is confusing.
>I half suspect it anyway. This is very new to me.
>
>As I said, EAV is an interesting concept, and one I'd rather know, so
>thanks for pointing it out, even if it's not related to this.
I would rather no -- as in "NO WAY!" -- EAV.
sincerely,
Gene Wirchenko
Computerese Irregular Verb Conjugation:
I have preferences.
You have biases.
He/She has prejudices. >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: Oct 20, 2004
Posts: 156
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(Msg. 9) Posted: Fri May 30, 2008 10:11 am
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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"Adriano Varoli Piazza" wrote in message
> As one of my first encounters with SQL (The RDBMS used is MySQL 5.1),
> my colleague and I have designed the following (it's a part of a
> catalog system for a museum):
> We have an "attachments" table, which can refer to "works_of_art",
> "people", "reproductions" (Let's say, more than three tables). So a
> work of art can have attachments, a person can have a different
> attachment, etc.
>
> To be able to relate each object to its eventual attachments, one
> solution I imagined is to put N foreign keys from each of the tables
> referred in attachments (if my use of the verb refer is incorrect,
> please do point it out). Let's say that, for now, there are no fields
> exclusive to any of the referred tables, so creating different
> attachment tables is not the best obvious choice.
>
> The alternative solution we came up with was to use two fields in
> "attachments" to identify the relations: one with the id of the
> referred table, and one with the "type". So 'works of art' would be 0,
> 'people' would be 1... The reasoning behind the decision was that my
> colleague felt that too many fields would remain empty with the first
> solution, and that adding a new type of "attachee" was simpler/more
> efficient than adding a new foreign key.
>
> This solution doesn't strike me as the best. We want to use cakephp to
> build the app that will use the database, and while this solution
> would eventually work with some manual labour, I feel it grates
> against it when the rest of the design does not. Since my knowledge of
> SQL is tenuous at best, I wanted to listen to some informed opinions
> about this before arguing again.
>
> By all means, if this is a WTF, point it out, the reason, and possibly
> an alternative.
If I understand your intention correctly then I am sorry to say it probably
is a WTF. I say "probably" because you actually describe two intentions.
In one place you talk about relating objects (sic) to attachments, and
immediately after that you talk about doing the opposite.
I suspect you are uncomfortable with the idea of multiple attachment tables
because superficially they would look the same (in the sense they'd have the
same column names, each of the same type). That is a programmer's point of
view. To a database designer they should appear to be VERY different and I
suspect that if you look deep into the logic of what one is justified in
doing with attachments for people versus attachments for works_of_art, those
differences will become apparent. Once you see that you will be perfectly
happy to have multiple attachment tables. The physical model would
correspond closely to the logical model.
That makes life easy because it makes it hard to write a correctly formed
query that executes correctly and yet gives a wrong or meaningless answer.
Database design is not about making it easy to do correct things so much as
it is about making it hard to inadvertently do wrong things, and rather
paradoxically (it seems to me) that often ends up making correct things easy
into the bargain.
Having offered an opinion, I ought to say you'd be unwise to follow any
specific advise you get from a newsgroup. We all have our own enthusiasms,
prejudices, and preconceptions of what you are trying to do.
Roy >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: May 29, 2008
Posts: 7
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(Msg. 10) Posted: Fri May 30, 2008 11:00 am
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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On May 30, 2:04 pm, Gene Wirchenko wrote:
> Adriano Varoli Piazza wrote:
>
> [snip]
>
> >A simple "Your post is very confusing, please clarify X, Y and Z"
> >would have been better.
>
> A clear post in the first place would be even better. I have
> things to do with my time. If my first impression of a post is that I
> can not easily understand it, why should I bother with it?
All well and good, but why reply in that case?
Saludos,
Adriano >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: May 29, 2008
Posts: 7
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(Msg. 11) Posted: Fri May 30, 2008 11:05 am
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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On May 30, 2:10 pm, Bob Badour wrote:
> Adriano Varoli Piazza wrote:
> > On 29 mayo, 22:11, Bob Badour wrote:
>
> >>Gene Wirchenko wrote:
>
> >>>Adriano Varoli Piazza wrote:
>
> >>>>On 29 mayo, 18:38, Bob Badour wrote:
>
> >>>>>I will cite Date's _Principle of Incoherence_ and ask whether you are
> >>>>>re-inventing EAV, yet again?
>
> >>>>Readinghttp://en.wikipedia.org/wiki/Entity-Attribute-Value_model,
> >>>>but this doesn't look like the same problem at first glance. I'll try
> >>>>to wrap my head around the concept.
> >>>>Though it does seem to be an awful lot of work for this particular
> >>>>task.
>
> >>>>Thanks for the readup anyway, if it's the right solution, good, and if
> >>>>it's not, I'll avoid reinventing stuff in the future.
>
> >>> It is not the right solution. It is a hideous way to do it.
>
> >>And I want to make clear I wasn't accusing the OP of anything hideous. I
> >>could not make enough sense of his post to tell what he was doing, and
> >>some of it seemed suggestive of yet another reinvention of EAV. Not
> >>enough to say for sure, though.
>
> > A simple "Your post is very confusing, please clarify X, Y and Z"
> > would have been better.
>
> No, actually, it wouldn't have. You might have preferred it, but it
> would have done you a lot more harm than good.
Ok, then this was a better reply than your original one. Though I
don't understand how asking me to rephrase my problem (thus rethinking
it) would do more harm.
> The only really useful and helpful thing I can say is: You need to learn
> the fundamentals before you start designing databases. And learning the
> fundamentals has nothing to do with learning the SQL language.
Yes, this is clear. I have the impression, though, that learning some
of the fundamentals implies a bit of experience in most real-life
cases. I could be wrong.
Saludos
Adriano >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: Jan 15, 2008
Posts: 1017
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(Msg. 12) Posted: Fri May 30, 2008 2:10 pm
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Adriano Varoli Piazza wrote:
> On 29 mayo, 22:11, Bob Badour wrote:
>
>>Gene Wirchenko wrote:
>>
>>>Adriano Varoli Piazza wrote:
>>
>>>>On 29 mayo, 18:38, Bob Badour wrote:
>>
>>>>>I will cite Date's _Principle of Incoherence_ and ask whether you are
>>>>>re-inventing EAV, yet again?
>>
>>>>Readinghttp://en.wikipedia.org/wiki/Entity-Attribute-Value_model,
>>>>but this doesn't look like the same problem at first glance. I'll try
>>>>to wrap my head around the concept.
>>>>Though it does seem to be an awful lot of work for this particular
>>>>task.
>>
>>>>Thanks for the readup anyway, if it's the right solution, good, and if
>>>>it's not, I'll avoid reinventing stuff in the future.
>>
>>> It is not the right solution. It is a hideous way to do it.
>>
>>And I want to make clear I wasn't accusing the OP of anything hideous. I
>>could not make enough sense of his post to tell what he was doing, and
>>some of it seemed suggestive of yet another reinvention of EAV. Not
>>enough to say for sure, though.
>
> A simple "Your post is very confusing, please clarify X, Y and Z"
> would have been better.
No, actually, it wouldn't have. You might have preferred it, but it
would have done you a lot more harm than good.
> Still, I'm not offended by people telling me I'm doing things the
> worst way, or telling me what I wrote is confusing.
> I half suspect it anyway. This is very new to me.
>
> As I said, EAV is an interesting concept, and one I'd rather know, so
> thanks for pointing it out, even if it's not related to this.
>
> Saludos
> Adriano
The only really useful and helpful thing I can say is: You need to learn
the fundamentals before you start designing databases. And learning the
fundamentals has nothing to do with learning the SQL language. >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: Jan 15, 2008
Posts: 1017
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(Msg. 13) Posted: Fri May 30, 2008 4:51 pm
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Adriano Varoli Piazza wrote:
> On May 30, 2:04 pm, Gene Wirchenko wrote:
>
>>Adriano Varoli Piazza wrote:
>>
>>[snip]
>>
>>>A simple "Your post is very confusing, please clarify X, Y and Z"
>>>would have been better.
>>
>> A clear post in the first place would be even better. I have
>>things to do with my time. If my first impression of a post is that I
>>can not easily understand it, why should I bother with it?
>
> All well and good, but why reply in that case?
Because in some rare instances one can help the other person by
replying. I have no idea how open minded, intellectually honest and
responsible you are until I broach the subject of the incoherence. >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: Jan 15, 2008
Posts: 1017
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(Msg. 14) Posted: Fri May 30, 2008 4:58 pm
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Adriano Varoli Piazza wrote:
> On May 30, 2:10 pm, Bob Badour wrote:
>
>>Adriano Varoli Piazza wrote:
>>
>>>On 29 mayo, 22:11, Bob Badour wrote:
>>
>>>>Gene Wirchenko wrote:
>>
>>>>>Adriano Varoli Piazza wrote:
>>
>>>>>>On 29 mayo, 18:38, Bob Badour wrote:
>>
>>>>>>>I will cite Date's _Principle of Incoherence_ and ask whether you are
>>>>>>>re-inventing EAV, yet again?
>>
>>>>>>Readinghttp://en.wikipedia.org/wiki/Entity-Attribute-Value_model,
>>>>>>but this doesn't look like the same problem at first glance. I'll try
>>>>>>to wrap my head around the concept.
>>>>>>Though it does seem to be an awful lot of work for this particular
>>>>>>task.
>>
>>>>>>Thanks for the readup anyway, if it's the right solution, good, and if
>>>>>>it's not, I'll avoid reinventing stuff in the future.
>>
>>>>> It is not the right solution. It is a hideous way to do it.
>>
>>>>And I want to make clear I wasn't accusing the OP of anything hideous. I
>>>>could not make enough sense of his post to tell what he was doing, and
>>>>some of it seemed suggestive of yet another reinvention of EAV. Not
>>>>enough to say for sure, though.
>>
>>>A simple "Your post is very confusing, please clarify X, Y and Z"
>>>would have been better.
>>
>>No, actually, it wouldn't have. You might have preferred it, but it
>>would have done you a lot more harm than good.
>
> Ok, then this was a better reply than your original one. Though I
> don't understand how asking me to rephrase my problem (thus rethinking
> it) would do more harm.
It doesn't matter how many times one rephrases things if one lacks the
basic understanding required for coherent analysis. Even if the result
sounds coherent, it's probably accidental, and the chances for mutual
comprehension are extremely low.
>>The only really useful and helpful thing I can say is: You need to learn
>>the fundamentals before you start designing databases. And learning the
>>fundamentals has nothing to do with learning the SQL language.
>
> Yes, this is clear. I have the impression, though, that learning some
> of the fundamentals implies a bit of experience in most real-life
> cases. I could be wrong.
Fundamentals first. Experience later. A person can work in this field
for 20 years and gain a year's experience 20 times, or a person can work
in this field for 20 years and gain 20 years experience.
Sadly, one can find too many of the former and too few of the latter. In
fact, the former abound. >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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External
Since: Nov 15, 2007
Posts: 1217
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(Msg. 15) Posted: Sun Jun 01, 2008 3:13 am
Post subject: Re: Multiple tables refer to one -To use foreign keys or not? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Adriano Varoli Piazza wrote:
>We have an "attachments" table, which can refer to "works_of_art",
>"people", "reproductions" (Let's say, more than three tables). So a
>work of art can have attachments, a person can have a different
>attachment, etc.
What is an attachment? I can understand the works of art, people and reproductions
but I don't know what you mean by attachment.
Tony
--
Tony Toews, Microsoft Access MVP
Please respond only in the newsgroups so that others can
read the entire thread of messages.
Microsoft Access Links, Hints, Tips & Accounting Systems at
http://www.granite.ab.ca/accsmstr.htm
Tony's Microsoft Access Blog - http://msmvps.com/blogs/access/ >> Stay informed about: Multiple tables refer to one -To use foreign keys or not? |
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semantics of foreign keys: domain specific inequality? - I'm trying to figure out how to deal with the relative importance of tables involved in a foreign-key relationship. My actual problem is one of generating HTML pages directly from database schemas (think of ruby-on-rails, django, etc.), and doing it in ...
Multiple keys and transition constraints - Given a relation schema R {A, B, C}, where A and B are each candidate keys. If the current extension is r {{A:1, B:9, C:3} {A:2, B:8, C:4}} and the proposed extension is r' {{A:1, B:8, C:4} {A:2, B:9, C:3}} is only A different? Or are both ...
Multiple-Attribute Keys and 1NF - I am still fighting with the theoretical underpinning for 1NF. As such, any comments would be greatfully accepted. The reason for my concern is that there /seems/ instances where 1NF is insufficient. An example occurred to me while I was wiring up a..
Multiple Parent Tables (or Multiple Inheritence, or - Hi, It seems to be a common enough problem, but it doesn't seem to ever be properly addressed in data modelling books, and from reading on the web its clear that other people have had this problem as well as had multiple solutions presented, but its.. |
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