Re: advice in model design - principally

[_Sebastian_]

Hi Bruno,

thanks for you search hints, maybe mine (database table layout...) was
not the best choice for what I was looking for.
I will give it a go again with your suggestions.

Thx

seb

On Jan 16, 1:29 am, bruno desthuilliers
 wrote:
> On 15 jan, 13:05, _Sebastian_  wrote:
>
> > Hy all,
>
> > I'm trying to replicate a existing project database as a conceptual
> > test.
>
> > I started off with creating a few models and I thought about ways on
> > how I could link and/or organise them. As I'm just starting to learn
> > django and python and my basic database knowledge is restricted to MS
> > products I want to get some basic things right.
>
> > I'm talking not about the technical bits on how to write modules,
> > fields and stuff I am thinking about how to organise tables, the
> > underlying principles and rules.
>
> This is nothing specific to django (or almost, cf below). Google for
> "relational model" and "relational database design",  and "normal
> form". Once you have a normalized data model, there may be a couple
> Django-specific stuff - mostly, Django doesn't (yet) support compound
> primary keys (so you'll have to use a surrogate key), and some
> contribs (like generic) requires an integer primarry key, so better to
> stick to it even if you do have a natural primary key.
>
> > I head a search and came 
> > acrosshttp://publib.boulder.ibm.com/infocenter/idshelp/v10/index.jsp?topic=...
> > which I am reading now but I was wondering if you know a better site
> > to read about this sort of question?
>
> After a very quick look, it seems that the section about design might
> be a good start.
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Re: advice in model design - principally

[bruno desthuilliers]

On 15 jan, 13:05, _Sebastian_  wrote:
> Hy all,
>
> I'm trying to replicate a existing project database as a conceptual
> test.
>
> I started off with creating a few models and I thought about ways on
> how I could link and/or organise them. As I'm just starting to learn
> django and python and my basic database knowledge is restricted to MS
> products I want to get some basic things right.
>
> I'm talking not about the technical bits on how to write modules,
> fields and stuff I am thinking about how to organise tables, the
> underlying principles and rules.

This is nothing specific to django (or almost, cf below). Google for
"relational model" and "relational database design",  and "normal
form". Once you have a normalized data model, there may be a couple
Django-specific stuff - mostly, Django doesn't (yet) support compound
primary keys (so you'll have to use a surrogate key), and some
contribs (like generic) requires an integer primarry key, so better to
stick to it even if you do have a natural primary key.

> I head a search and came across 
> http://publib.boulder.ibm.com/infocenter/idshelp/v10/index.jsp?topic=...
> which I am reading now but I was wondering if you know a better site
> to read about this sort of question?

After a very quick look, it seems that the section about design might
be a good start.


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Re: advice in model design - principally

[Kenneth Gonsalves]

On Thursday 15 Jan 2009 6:04:13 pm _Sebastian_ wrote:
> Could you elaborate on what you mean with 'then break them a bit for
> speed'?

well, 3 normal forms is the ideal - but we live in a real world. So after 
normalising the database, it is often found that repeating a field, or adding 
a field that can be calculated from existing fields in a table speeds up 
things enormously without significantly compromising database integrity. So 
we do it. It may not be necessary in a smaller database, but may be needed in 
a bigger one. 

-- 
regards
KG
http://lawgon.livejournal.com

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Re: advice in model design - principally

[_Sebastian_]

Kenneth,

thank you for your reply.

Could you elaborate on what you mean with 'then break them a bit for
speed'?

 - seb

On Jan 15, 11:22 pm, Kenneth Gonsalves  wrote:
> On Thursday 15 Jan 2009 5:35:56 pm _Sebastian_ wrote:
>
> > I head a search and came across
> >http://publib.boulder.ibm.com/infocenter/idshelp/v10/index.jsp?topic=...
> >bm.ddi.doc/ddi27.htm
>
> basically you would need to read up on the first three normal forms, try to
> implement them and then break them a bit for speed if needed. Any site that
> describes the normal forms is ok for that - this one seems ok.
>
> --
> regards
> KGhttp://lawgon.livejournal.com
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Re: advice in model design - principally

[Kenneth Gonsalves]

On Thursday 15 Jan 2009 5:35:56 pm _Sebastian_ wrote:
> I head a search and came across
> http://publib.boulder.ibm.com/infocenter/idshelp/v10/index.jsp?topic=/com.i
>bm.ddi.doc/ddi27.htm

basically you would need to read up on the first three normal forms, try to 
implement them and then break them a bit for speed if needed. Any site that 
describes the normal forms is ok for that - this one seems ok.

-- 
regards
KG
http://lawgon.livejournal.com

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advice in model design - principally

[_Sebastian_]

Hy all,

I'm trying to replicate a existing project database as a conceptual
test.

I started off with creating a few models and I thought about ways on
how I could link and/or organise them. As I'm just starting to learn
django and python and my basic database knowledge is restricted to MS
products I want to get some basic things right.

I'm talking not about the technical bits on how to write modules,
fields and stuff I am thinking about how to organise tables, the
underlying principles and rules.

Is it better to have more tables with fewer rows and link them. Or
habe one large table...

For the purpose of my test the project db will consist of many
datasets for one project each. I would say that 90% of the Columns/
fields could be linked to a project number.
Would that mean they should all be in one table, 100 or more columns?
If not how should I organise them and link the separate tables?
How do I decide what should go into a extra table?
I know that it makes sense to have inn each project reoccurring
selections as a linked table, but what else is there to know?

I head a search and came across
http://publib.boulder.ibm.com/infocenter/idshelp/v10/index.jsp?topic=/com.ibm.ddi.doc/ddi27.htm
which I am reading now but I was wondering if you know a better site
to read about this sort of question?

Thanks in advance.

seb
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