Thanks Kevin, I'm still not clear on this. You mentioned below that I'd need three tables in addition to 'plant', but I see:
plant, characteristic, provides, needs, provides_characteristics, and needs_characteristics. Am I right that this means that each characteristic must be duplicated for the provides and needs relationships it will have with 'plant' and their is no way of keying two relationships with plant off the same table? On Jun 1, 5:33 pm, kevinpfromnm <[email protected]> wrote: > it sounds like what you are describing would need 3 additional tables > in addition to the plants table. > plant > > characteristic > > provides join > needs join > > plant has many provides_characteristics and many provides through > provides characteristics > plant has many needs characteristics and many needs through needs > characteristics > > then you can start looking at a characteristic and seeing what plants > have and need it relatively easily. otherwise, you can add a flag on > a single join table that tells whether it's a provides or a needs... I > think the 4 table approach though will be easier to write views and > such for as there is a clear functional division between the provides > and needs relationships, even if the data difference is negligible. > > On Jun 1, 2:40 pm, Ronbo <[email protected]> wrote: > > > 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 -- You received this message because you are subscribed to the Google Groups "Hobo Users" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/hobousers?hl=en.
