Store multiple objects (tables...) in one file?

[Michael Gerbracht <smartmails@arcor.de>]

I am currently developing a program that can handle multiple tables and
graphs. I would like to be able to save the whole project in one file.

I would like to use the open document format but I wonder whether there is
some kind of meta format definition which allows you to save multiple
tables and graphs in one JAR file.
Or is there a way to save multiple tables (each having multiple sheets) in
one ODS file, for example?

If there is no official solution for this, do you know of anybody else who
has implemented something like that?

Thank you very much,
Michael Gerbracht