Synthetic Feed issues:

["Bob Wyman" <bob@xxxxxxxx>]

	There is a trend towards more software that creates "synthetic
feeds." i.e. constructing secondary feeds based on the content of one
or more source feeds. Sebastian Paquet gives a good overview of the
various operations involved in constructing synthetic feeds in his
blog at: http://radio.weblogs.com/0110772/2003/09/11.html#a1098 .
Note: his note is basically a review of the relevant set operations
(union, intersection, etc.)
	I haven't been able to find a good discussion of the Atom
issues related to synthetic feeds. If such a discussion has taken
place, please point me to it. In the meantime, a few
comments/questions:
	Synthetic feeds can be very useful. However, processing of the
existing RSS feeds indicates a number of problems that arise when one
attempts to construct a synthetic feed from a combination of "source"
feeds that may contain previously generated synthetic feeds. The
problem is, of course, that if you are using synthetic feeds as the
input to a feed synthesizing process, it becomes very easy to generate
duplicate entries. i.e. you might get the "same" entry from two
synthetic feeds but consider them different because of reformatting
differences or simply because they come, most recently, from different
feeds.
	As one who is building software that synthesizes feeds, I
think it would be very useful to have a Feed attribute that states
that a feed is a secondary, synthetic feed rather than a primary
source. Has such an attribute been discussed and/or proposed in the
past? A simple Boolean attribute would do the trick (i.e.
atom:primary) although that might be a bit terse and difficult to
extend in the future...
	Also, I'm curious about the Feed attributes "author" and
"contributor" when applied to a synthetic feed. What should the
correct values be? Is the author the maintainer of the synthetic feed?
Or, should the "author" information be only in entries? If that is the
case, what should the synthesizer do if a source feed does not contain
an author attribute for some entry that is inserted into the
synthesized feed? 
	Similar questions apply to the "contributor" attribute. Should
the synthetic feed combine all the "authors" and "contributors" from
source feeds into the similar positions in the synthetic feed? Or,
should source "authors" and "contributors" be left to the individual
entries themselves? 
	Is a feed synthesizer allowed to make any changes to the
content of an entry? Some systems may wish to remove specific fields
from an entry to make an entry smaller, summarize the entry, insert
additional attributes, etc. If so, should the various attributes like
atom:id, atom:modified, etc. be changed? If atom:id must change, then
how does or can one indicate the source entry? (I can see how to
specify a link to an "alternate", but can't see how to point to an
"original" of which a current link might be an "alternate.")

		bob wyman