Below I think I have worked out how one can in fact have a top20
feed, and
I show how this can be combined without trouble with the
<history:next ...>
link...
On 29 Jul 2005, at 13:12, Eric Scheid wrote:
On 29/7/05 7:57 PM, "Henry Story" <[EMAIL PROTECTED]> wrote:
1- The top 20 list: here one wants to move to the previous top 20
list and
think of them as one thing. The link to the next feed is not meant
to be
additive. Each feed is to be seen as a whole. I have a little
trouble still
thinking of these as feeds, but ...
What happens if the publisher realises they have a typo and need to
emit an
update to an entry? Would the set of 20 entries (with one entry
updated) be
seen as a complete replacement set?
Well if it is a typo and this is considered to be an insignificant
change then
they can change the typo in the feed document and not need to change
any updated
time stamps.
The way I see it, maybe a better way would be to have a sliding
window feed
where each entry points to another Atom Feed Document with it's own
URI, and
it is that second Feed Document which contains the individual items
(the top
20 list).
This is certainly closer to my intuitions too. A top 20 something is
*not* a feed.
Feed entries are not ordered, and are not meant to be thought of as
a closed
collection. At least this is my initial intuition. BUT....
I can think of a solution like the following: Let us imagine a top 20
feed where
the resources being described by the entries are the position in the
top list. So
we have entries with ids such as
http://TopOfThePops.co.uk/top20/Number1
http://TopOfThePops.co.uk/top20/Number2
http://TopOfThePops.co.uk/top20/Number3
...
Each of these resources describes the songs that is at a certain rank
in the top of
the pops chart. Each week the song in that rank may change. When a
change occurs in the
song at a certain rank the top 20 feed with id
http://TopOfThePops.co.uk/top20/Feed
will contain a new entry such as
<entry>
<title>Top of the pops entry number 1</title>
<link href="http://TopOfThePops.co.uk/top20/Number1/"/>
<id>http://TopOfThePops.co.uk/top20/Number1</id>
<updated>2005-07-05T18:30:00Z</updated>
<summary>Top of the pops winner for the week starting 5 July
2005</summary>
</entry>
A client that would subscribe to such a feed would automatically get
updates every
week for each of the top 20 resources. But the feed could be
structured exactly like
I suggest in 2.
So for a top 2 feed (20 is a bit to long for me)
<feed>
<title type="text">My top 2 Software Books</title>
<id>http://bblfish.net/blog/top2</id>
<history:prev>http://bblfish.net/blog/top2/
Archive-2005-07-18.atom</history:prev>
...
<entry>
<title>My Top 1 book</title>
<link href="http://bblfish.net/blog/top2/Number1/"/>
<id>http://bblfish.net/blog/top2/Number1</id>
<updated>2005-07-25T18:30:00Z</updated>
<summary>My top 1 book is Service Oriented Computing by Wiley</
summary>
</entry>
<entry>
<title>My Top 2 book</title>
<link href="http://bblfish.net/blog/top2/Number2/"/>
<id>http://bblfish.net/blog/top2/Number2</id>
<updated>2005-07-25T18:30:00Z</updated>
<summary>My second top book is "xml in a Nutshell"</summary>
</entry>
</feed>
The above representation of the http://bblfish.net/blog/top2 feed
points to the
archive feed http://bblfish.net/blog/top2/Archive-2005-07-18.atom
<feed>
<title type="text">My top 2 Software Books</title>
<id>http://bblfish.net/blog/top2</id>
...
<entry>
<title>My Top 1 book</title>
<link href="http://bblfish.net/blog/top2/Number1/"/>
<id>http://bblfish.net/blog/top2/Number1</id>
<updated>2005-07-18T18:30:00Z</updated>
<summary>My top 1 book is Java 2D Graphics</summary>
</entry>
<entry>
<title>My Top 2 book</title>
<link href="http://bblfish.net/blog/top2/Number2/"/>
<id>http://bblfish.net/blog/top2/Number2</id>
<updated>2005-07-18T18:30:00Z</updated>
<summary>My second top book is "xml in a Nutshell"</summary>
</entry>
</feed>
As you notice only the top1 has changed from the first week but not
the
second, and yet in both feeds there is an entry for both. A non
change can
sometimes be an important event. But this is really up to the feed
creator
to choose how to present his feeds. He could easily have had only had
the
entry for http://bblfish.net/blog/top2/Number1 in the first feed.
Looking at it this way, there really seems to be no incompatibility
between
a top 20 feed and the <history:next ...> link. My talk about archives
not
changing should be more precisely about archives not changing in any
significant way. And this advice could be moved to an implementors
section
and be encoded in HTTP by simply giving archive pages an infinitely long
expiry date.
Someone could subscribe to that second feed and poll for updates,
and all
they'll ever see are updates to the 20 items there, not the 20
items from
the next week/whatever.
The idea of feeds linked to feeds has lots of utility -- feeds of
comments
for one, and even a feed of feeds available on the site.
I completely agree. And remember for any two things there is at least
one way they
are related. And there are many different ways feeds can be related
to each other.
A feed may be an archival continuation of one - which is what the
<history:next ...>
link in my opinion addresses, but there are many other ways one can
relate feeds.
For example: this HTML page <http://www.nature.com/rss/> has an
equivalent
feed document <http://npg.nature.com/pdf/newsfeeds.rdf>, where each
item
links to the individual feeds for each publication. That feed
doesn't update
often, mostly because NPG doesn't add many new feeds to their site
all that
often. The URIs the entries of that feed link to are redirected to the
permanent URIs of the current issue (each issue has it's own feed
which is
the table of contents for that issue, with a distinct and separate
URI for
each issue).
Yes a feed can itself be an entry in another feed.
It's conceivable they could also provide a feed for each publication
pointing to the table of contents feeds of each issue. That is, a
feed with
an entry for each issue.
yes.
Of the above, the mechanism of a single URI which redirects to the
current
issue is a situation which would still need a flag indicating that the
appropriate thing to do is to not persist older entries.
I am starting to wonder whether this is really needed now that I have
looked
at the top20 example I gave above.
The other structure of feeds linking to feeds would require the
aggregator
be able to do something useful with such links, but this can be
generalised
and thus be useful for many purposes. As it is, right now with NNW
I can do
something useful with such a feed: drag & drop the item headline
link to my
subscriptions pane to subscribe to that feed and view the entries
therein.
I myself have no problem with feeds being entries, feeds pointing to
other
feeds, or anything like that. A feed is a resource. It can change. A
feed
is simply a set of state changes to resources. It is that general.
Both require coding effort.
e.
