[Design] RSS in Cosmo for event change notification

[Mitchell Kapor]

I propose we seriously look into developing a notification capability  
in Cosmo 0.4.  The main use case to be supported is notification of  
recent event changes via an RSS feed of a calendar published on Cosmo.

This is of particular use when a calendar has a reader who is NOT the  
writer of events, e.g., Esther keeps my calendar and adds  
appointments to it.  As it now stands, if I want to be sure whether  
an appointment has been finalized I either have to look through  
future weeks or ask Esther.  Neither of these methods are very  
efficient.  It would be easier if I simply received a notification  
that my calendar had changed.  Then I would know for sure.

Cosmo already has RSS support in 0.3.  The trick now is to make it  
useful with the least amount of work.  What is of interest are recent  
changes to the calendar.  It doesn't matter what the date of an event  
is, per se, but that it has been changed, i.e., added, deleted, or  
modified.

If Cosmo is able to keep track via a timestamp of event changes, that  
would be the basis of the feed.  In the simplest possible useful  
implementation (which is where I think we should start), Cosmo would  
maintain an RSS feed of, say, the last 7 days of changes.

My expectation is that this would be good enough to make it  
worthwhile to use any RSS reader to subscribe to this feed.  New  
changes would show up as unread items.  It's as simple as that.

One virtue of this approach is that it allows us to add useful  
functionality to the overall Chandler system at a rate more like the  
speed of web development and less like the usual rate of Chandler  
client development itself (which is slow because it's the nature of  
the beast).

Extended functionality:  The RSS reader is Chandler could be brought  
to a point of usefulness that it could be used rather than an  
external RSS readers.  This would be nice, but it is not necessary.   
Or could happen later.

There could be user control of the number of days of recent changes  
to be kept in the feed.  Again, nice but not necessary.

Another nice-to-have would be the ability to click on a link in the  
body of the feed item and be taken to the detail view of that event  
in Chandler (or Scooby).

Question:

Is it easy to develop a feed that somehow distinguishes between  
additions, modifications, and deletions?