Hello,

I have a beginner's question about modeling. The application I am
working on is a plant database. One of the critical features is that
it make it easy to represent symbiotic relationships (like the 3
sisters in Mexico, squash, beans and corn), and to discover potential
new relationships.

So I have a plant model with some core characteristics describing a
species. I would like to be able to assign certain attributes by which
a plant has relationships with other species, such as:

shade
fixes_nitrogen
scaffolding (corn provides a scaffold for beans to climb)
Micronutrients
etc.

These would be another table.
So far, easy.

Plants can have one of two types of relationships with these
characteristics. Either 'need' or 'provide'. So a plant could provide
shade and need scaffolding, while another needs shade and provides
scaffolding...

Question: can this be represented with just two tables, and if so, how
to go about it, or do I need to duplicate these characteristics in
'needs' and 'provides' tables? From the little I know about
polymorphic associations, this seems different.

Many thanks

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