Add data models.

drafts/data_flows.rst

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+Mapping model use cases to matrix models (Room, Message, etc)
+=============================================================
+
+To think about:
+ - Do we want to support the idea of forking off new rooms from existing ones? This
+   and forums could benefit from it.
+
+Bug tracking UI
+---------------
+::
+
+ Projects => Rooms
+ Issues => Message Events
+ Comments => Message Events (relates_to key)
+
+Projects:
+ - Unlikely that there will be 100,000s of issues, so having to pull in all the issues for a project is okay.
+ - Permissions are usually per project and this Just Works.
+ - New issues come in automatically and Just Work.
+ - Can have read-only members
+
+Issues:
+ - Don't really want 1 Room per Issue, else you can have thousands of Rooms PER PROJECT, hence choice for    
+   Issues as Messages. Don't need to join a room for each issue.
+ - Idea of issue owner is clear (sender of the message)
+ - Updating issues requires an additional event similar to comments (with ``relates_to``)? Could possibly
+   be state events? Don't really want all the history if say the priority was changed 1000 times, just want
+   the current state of the key.
+
+Comments:
+ - Additional event with ``relates_to`` key.
+
+
+Forum
+-----
+::
+
+ Forum => Room (with pointers to Board Rooms)
+ Boards => Room (with pointers to Thread Rooms)
+ Threads => Room
+ Messages => Message Events
+
+Forum:
+ - Contains 10s of Boards.
+ - Contains special Message Events which point to different rooms f.e Board.
+
+Boards:
+ - Contains 100s of Threads.
+ - Contains special Message Events which point to different rooms f.e. Thread.
+
+Threads:
+ - Contains 100s of Messages.
+
+Can't do this nicely with the current Federation API because you have loads of
+Rooms and what does posting a message look like? Creating a thread is done by..?
+The user who is posting cannot create the thread because otherwise they would be
+the room creator and have ultimate privileges. So it has to be created by a bot
+of some kind which ties into auth (Application services?). To follow a board,
+you need a bot to join the Board Room and then watch it for changes... 
+
+Fundamental problem with forums is that there is only 1 PDU graph per room and
+you either have to pull in lots of graphs separately or one graph and filter it
+separately to get to the desired sub set of data. You have to subscribe into a
+lot of graphs if you subscribe to a board... If you have the entire board...
+good luck scrollbacking a particular thread.
+
+
+Google+ Community
+-----------------
+::
+
+ Community => Room (with pointers to Category Rooms)
+ Category => Room
+ Post => Message Events
+ Comment => Message Events (relates_to key)
+
+Community:
+ - Contains 10s of categories.
+ - Contains special Message Events which point to different rooms f.e Category.
+ - Moderators of the community are mods in this room. They are in charge of making
+   new categories and the subsequent rooms. Can get a bit funky if a mod creates a
+   category room without the same permissions as the community room... but another
+   mod can always delete the pointer to the buggy category room and make a new one.
+ - Do we want to support the idea of forking off new rooms from existing ones? This
+   and forums could benefit from it.
+
+Category:
+ - Contains 1000s of posts.
+ - Same permissions as the community room. How to enforce? Fork off the community
+   room?
+
+Posts:
+ - Contains 10s of comments.
+
+This is similar to forums but you can more reasonably say "screw it, pull in the
+entire community of posts."
+