[Zope] Permission-problem or bad design?

[Petter Holmström]

Hello list,

I've run into a rather interesting design problem that I don't know how 
to solve.

I'm creating a group calendar (in Plone). There are two kinds of event 
objects, an Event object and an Event Reference object. They are used in 
the following way:

Person A organizes a meeting to which he invites persons B and C. He 
then creates an Event object i his calendar and Event Reference objects 
in B's and C's calendars. The Event Reference contains all the fields of 
the event object (marked as read-only) plus two editable fields, one 
reference field to the original event object and a boolean field 
(accept/reject). Both the event objects the reference objects use the 
same view-page. So far no problems.

Now every event can be either public, semi-public ("busy") or private. 
This means that even though A has marked the event as semi-public, B and 
C must have full read-rights to the event. What's more, if B marks his 
reference as public, visitors must be able to get full read-rights to 
A's event through B's event reference. I've figured I'd need some kind 
of object-based security and not user-based, i.e. instead of giving the 
B-user rights to A's event I'd give the B-user's event rights to A's event.

Phew. This sure sounds complicated. :-) Perhaps some ascii-art will make 
it clearer:

[A's calendar]
  |
  +--- Base Event <-+------+---(busy)------> anonymous user *)
                    |      |
                 (public)  |
[B's calendar]     |      |
  |                 |      |
  +--- Reference >--+------|---(public) ---> anonymous user **)
                           |
                         (public)
[C's calendar]            |
  |                        |
  +--- Reference >---------+---(private) --> anonymous user ***)


*) Anonymous user has limited rights to A's base event.

**) Anonymous user has full read rights to B's reference, which gets its 
data from A's base event, to which the anonymous user has limited rights.

***) Anonymous user has no rights at all to C's reference.


I really don't know how to achieve this with the current security model 
of zope. Is there a better way to solve this problem? Did you even 
understand my dilemma?

Thanks,

-Petter-