Permaculture Database

[Rich Morris <mailinglists@pfaf.org>]

jedd wrote:
> On Thursday 05 April 2007 9:41 am, Paul Cereghino wrote:
> > This has been repeated by others.  I know I am confused and others may
> > be as well.  Is there a specific table and relationship structure that
> > you db-designers think of when I say hierarchy?  Are there basic
> > alternative models of adding attributes to objects that need to be
> > selected among?!
> >
> > for example..... [The Chicken]
> >
> > what are the different data structure choices... not for describing the
> > relationship of the chicken to other objects... but of describing the
> > characteristics of the chicken.... size, longevity, lifeform, breed, etc...
>
>  The latter isn't hierarchical - the attributes of the object are
>  what you're talking about there - average | max life, size ranges,
>  egg productivity, feed requirements, placidity, etc.
>
>  I'm not a db expert, but I can't conceive of creating a schema
>  that would be inherently hierarchical.
>
>  The nature of family/genus/species is hierarchical, f.e., but the way
>  you'd represent it in a db isn't, at least not to my mind.  I'm
>  intending to write some thoughts up about schema design soon,
>  anyway, as it happens.
>
>  Oh, when you say adding attributes to objects, do you mean the
>  values of those attributes, or adding new attributes?  The problem
>  with the latter is that although the db can be designed to cope with
>  this (though it takes a lot of effort to abstract things out to do so)
>  the application suite that uses that db needs to know the attributes,
>  so it can start doing sensible things with the data (attributes and
>  values).  Adding attributes typically is a couple of lines of SQL,
>  but a non-trivial change at the application layer.

It depends how you define your tables. Having an attribute a a column in 
a table would make things hard to expand. Having a separate table for 
attributes

plant_id | attribute_name | attribute_value

makes things much easier to expand.

        Rich

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