hello james.
With HTTP pipelining those multiple GETs shouldn't have that much of a
negative impact, although I'll admit that in practice pipelining does
have potential problems.
But even without pipelining, after the first feed retrieval, I would
still expect those multiple GETs to be more effecient on subsequent
updates. Two small GETs to retrieve one new feed entry would seem more
efficient than one giant GET of a 20 entry feed when you only want the
latest entry (unless you're also supporting RFC3229+feed?)
I guess this does depend to a some extent on the nature of your data,
the frequency of updates, and the kind of clients you expect to have.
of course it does. and please not that everything i propose is entirely
optional, of course. if you want to do it old-style, then that's fine.
but in particular in the case of push with fat ping, there is a very
substantial difference between being able to receive the data in the
required format via push updates, or having to GET the alternate version
of every single update.
I still think you are going about it the wrong way. If the content-type
for Atom doesn't sufficiently distinguish between the types of feed you
want to serve for HTTP content negotiation to work, it seems to me you
should be looking at ways to extend the content-type (like the type
parameter that was proposed to distinguish between Atom entry documents
and Atom feed documents). Inventing a new form of content negotiation
that requires parsing links from the top of an Atom feed is just twisted.
i am not saying that i am proposing the perfect solution, and there are
certainly different ways of approaching the problem i am looking at. it
seems to me, however, that changing the way how this could be done in a
more perfect way would require a lot of very substantial changes to the
core of media types and HTTP content negotiation. it would be very nice
to have HTTP content negotiation doing this, but unfortunately, atom
sort of "hides" the "real content" (the /feed/entry/content) from
visibility on the HTTP level.
But the real problem may just be an inappropriate use of Atom as a
general purpose container format. If you have a client that prefers
content as RDF, why not give them a true RDF feed? Why RDF embedded in
Atom? That kind of misses the point of RDF. Even worse, if a client
prefers JSON, do you really think it makes sense to serve them that JSON
as base-64 encoded blobs inside an XML container? I can assure you that
nobody is going to thank you for that option.
saying that atom is inappropriate as a general purpose container format
is your opinion. i happen to think that atom is exactly that. afaik, RDF
does not have feeds, and if i as a service designer choose to model my
service in a RESTful way based on atom abstractions, then atom probably
is a very good way to represent that. serving RDF content as well would
just be a convenience feature for those who would prefer to get RDF
representations of what my service exposes.
here is something i wrote a while ago about atom as a general container:
http://dret.typepad.com/dretblog/2009/05/atoms-future-as-a-generalpurpose-format.html
you might not agree with what i am saying here, but there are more and
more services where feeds are used as the RESTful abstraction of the
service model, and this is the area i am looking at for the proposal i
have made.
If you served RDF clients a real RDF feed, and JSON clients a real JSON
format, then you could be using standard HTTP content negotiation - at
least for most cases. If you wanted to provide an "HTML friendly" feed
that was separate from the one with raw XML embedded, you'd still need a
way to differentiate between the two, but at that point I would think it
not worth the complication. I'd just make your feed content the raw XML,
include a short summary, and then an alternate link to a more detailed
HTML page if really necessary.
again, you're saying "real RDF feed" and "real JSON feed" and these are
not things i am aware of. it might be interesting to think of RDF and
JSON serializations of the atom data model, but this would actually be
very hard to do well because of atom's openness and support of XML
namespaces. it's a very different discussion anyway, but we are
currently in the process of encoding atom as an RDF ontology, and i can
tell that it's suprisingly complicated.
so my assumption is to have atom XML as the feed container so that there
is only one representation of the feed abstraction that can be handled
by intermediaries, value-added components (such as push frameworks), and
then make sure that various types on content can be transported in that
framework in a well-defined and flexible way.
cheers,
dret.
--
erik wilde | mailto:[email protected] - tel:+1-510-6432253 |
| UC Berkeley - School of Information (ISchool) |
| http://dret.net/netdret http://twitter.com/dret |
