Re: ETag and resource representations

On 4 September 2013 00:19, Hubert A Le Van Gong <[email protected]> wrote:

> Hi Nicholas,
>
> I'm not sure why I should consider those as different resources. Isn't that
> what representations are for?

'representations' are different presentations/formats/content-types
showing the same (sub-)set of data. Page 2 does not contain the same
data as page 1, so isn't a different representation per the http
meaning of the noun, but a different resource. The entire library, if
not available via a single URL, is not a (HTTP) resource. (Someone
please correct me if I'm wrong there.)

> Besides, I'm not sure it makes it easier on the caching management side of
> things as those different resources are nonetheless linked (if an adult
> purchases a chid book, both the adult library and the child library
> resources are impacted).

The whole goal of a well-written web service is to improve a cache's
ability to make a match.
You said "The view of that resource (i.e. the list of books returned)
may vary based on the age of the reader (or any other criteria)."
How are you determining what 'view' to return, or put another way, how
do you decide on the "age of the reader"? Are readers users who have
to log in and get a cookie set? Or are readers just a target audience
for the book, and the client is asking for "children's books" through
some query string, the client's age being unknown?
If at the moment you're using something like Vary: Cookie to serve
different pages to different clients, then your resources are not
going to see any caches except the client's browser. Try to eliminate
this if at all possible, perhaps via 303 responses to avoid changing
the referring href.
If you are using query strings to change the books shown, then, as the
query string is part of the URL, and the URL is the minimal key
required to differentiate resources, a different URL means you are
requesting a different resource, and so the URI can be anything you
want, e.g. /childrens-books/ or /library?genre=children%39s

This isn't really relevant to Entity Tags but I thought I should bring it up.

-- 
Nicholas.