best practice?

Hi all

I'm currently involved in a project where a ressource

planning system is developed. We are using the

datetime.* libs for that purpose. 

Values of occupied ressources

are stored in a database. For a intersection wether a

ressource is free or occupied we are using

DateTime::SpanSet. But now the problem:

I have to be able to associate a database object 

with a given SpanSet which I create when retrieving

the data from the database. 

spans:

     [.n.][.n.][.n.]            -> new reservation

[.a.][.a.][.a.][.b.][.b.][.c.]  -> existing data

intersection gives conflicts with a & b which is correct
but i loose the context which of the dt objects belongs
to which data object.

First approach was to inherit from DateTime and
storing object references. But when I intersect_span
the sets, I'm loosing my references, seems that the dt
objects are newly created.

How can I solve that problem. If it is helpful I can
attach the inheritet DateTime code

Thank you very much for your help and sorry for the
bad english.

Regards Herbie