DAG structure / hard links / shared subtrees

[Jan Kybic <kybic@fel.cvut.cz>]

Dear org-mode users,

this is my first post, so let me first state that I am using org-mode
more and more for organizing my daily agenda and I find it really
useful.

I have a feature request. The structure of the org file is a tree. 
I wondered if it could be made a directed acyclic graph (DAG) instead. 
In other words, could a subtree be shared between two trees? In yet
another words, a kind of Unix directory structure with hard links.

One possible use case is as follows: I am preparing a meeting that
concerns several projects. I have my org file structured by projects. I
want to prepare an agenda for this meeting, which would contain the
issues to discuss from the projects. I want to be able choose the order
the issues. During the meeting, I want to add notes. Right now, I see the following
options:

a) I can copy the subtrees corresponding to issues from the projects. 
   However, if I later edit either of the copies, I would need to
   synchronize the changes manually.

b) I can make an internal link from the agenda to the issues. However,
   the agenda would then not contain the full detail of the issues, just
   a short part of the headline. During the meeting I would have to jump
   there and back.

c) I can create the meeting agenda dynamically, by assigning tags to
   projects and creating a sparse tree, e.g. from the Agenda
   buffer. However, this requires me to mark every issue to be discussed
   with a meeting-specific tag. I do not have much control over the order
   in which the issues appear. I cannot structure them. The generation
   takes time. And it is not straightforward to add new items to the
   meeting.

I am not familiar with the internals of the org-mode but I can envision
several possible implementations:

a) Enhance existing links so that they can be expanded in-place to show the
   whole subtree, not just a start of the headline. Ideally, it should
   be possible to make changes there but a read-only access would also help.

b) Physically copy "linked" trees to the new location. Make the copies
   share an Id but have a unique subId. Then when one of the copies is
   changed, the changes are propagated into other copies. I believe 
   a lot of the logic could be borrowed from org-mobile, which also
   performs synchronization.

What do you think, does it sound feasible? Is there any other way to
achieve what I want with org-mode? 

Thank you very much and keep up the good work.

Yours,

Jan


-- 
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Jan Kybic <kybic@fel.cvut.cz>               tel. +420 2 2435 5721 or 5877
http://cmp.felk.cvut.cz/~kybic                              ICQ 200569450