Just mulling on this now.

If you have a start and end value for each element then you could plot each element on an xy chart. Then to get the ones you want you could select an area on the chart which matches your criteria.

Now my copy of 'Mastering Algorithm with Perl' has chapters on both graphs and sets. This might be a fruitful line of study.

On the database front Postgres has lots of builtin coordinate functions - although you're better off in Perl me thinks.

I should have taken CS instead of Physics - alas I can be of no more help until I hav eread up some more...