Re: How to force two entities to point to the same lookup value

Giraffe wrote:

> Hi all,
>
> Please bear with me I've tried to make my question as terse as possible,
> whilst not appearing confusing (hopefully I've not failed in this regard).
>
> I'm trying to store a Chart configuration in an Oracle database
> (although I'm hoping that my choice of database will not lead to a
> solution specific to it, since so far my database is not platform, or
> database specific).
>
> One of these chart entities has two or more axes (one x and at least one
> y) related to it, and each axis relates to zero or more plot entities
> (which store plot information such as plot type, line or columns/bars
> etc). these plot entities relate to a specific item of data that can be
> plotted (and relates to a Unit table).
>
> So far I have
>
> relations-> Chart (1-3) Axis (0-many) Plot (Many-1) DataItem
>
> (I'm assuming I've got this relationship right)
>
> How can I now insert a relationship with a Unit entity so that I can
> ensure that Axis and Plot can refer to any unit in the unit relation *so
> long as its the same Unit*. I'd like to enforce at a relational level a
> limitation so that any number of plots can be configured for a specific
> axis so long as they are all of the same unit. For instance income and
> outgoings can both be related to an axis since they share the same unit
> of currency. But weight and income cannot be plots that relate to one
> axis since there are two units here and an axis can refer to only one unit.
>
> It's easy to enforce this in my application but I was hoping to somehow
> put in some kind of constraint at the database level to stop people
> setting up charts with an axis that allows income, weight, and time to
> all be plotted on the same axis.
>
> Perhaps someone has stored a chart configuration in a database before
> and can offer me some insight.
>
> Many thanks,

You may have a pragmatic argument for relaxing irreducibility and simplicity in your choice of candidate key for Axis. Received on Sat Aug 12 2006 - 17:41:04 CEST