On Nov 22, 2005, at 3:19 , Dennis Veatch wrote:
> I had thought just adding some fields called topsoil_start/
> topsoil_end,
> gravel_start/gravel_end, etc. But them I'm left with how to take
> those values
> and give to total depth for each layer and total depth of the well.
>
> But I'm not sure that is the best way to handle this.
>
> Does anyone have some other suggestions?
This is similar in concept to temporal intervals. You might want to
look at "Temporal Data and the Relational Model" by Date, Darwen, and
Lorentzos for general theory, and "Developing Time-Oriented Database
Applications" by Richard Snodgrass for implementations in SQL. The
latter is available as a PDF download (the book itself is out of print):
http://www.cs.arizona.edu/people/rts/tdbbook.pdf
Hope this helps!
Michael Glaesemann
grzm myrealbox com