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Re: (Possibly) core issue on identification with EPUB-WEB, packaging, fragments...

From: Brady Duga <duga@google.com>
Date: Mon, 01 Jun 2015 14:58:46 +0000
Message-ID: <CAH_p_eU_onvdpv2KEfa2VKueWbKfpznQKEQbEnMu8DjB_H4gHA@mail.gmail.com>
To: Nick Ruffilo <nickruffilo@gmail.com>, Ivan Herman <ivan@w3.org>
Cc: W3C Digital Publishing IG <public-digipub-ig@w3.org>, Ralph Swick <swick@w3.org>
If there is no package file, do these problems still exist? It seems like
that is mentioned in the original email, but I am not sure if any of these
cons apply to it.

On Mon, Jun 1, 2015 at 7:12 AM Nick Ruffilo <nickruffilo@gmail.com> wrote:

> What if we leave it up to the client/server to determine what the root of
> the package is and handle it approrpiately?
> So, an epub-web object (or whatever we call it) might live at :
> //my/item/awesome.epub
> To address a specific FILE in that, you go to
> //my/item/awesome.epub/text/chap2.html
> To get to a fragment, you just use # in reference to whatever the fragment
> is:
> //my/item/awesome.epub/text/chap2.html#first_header
> //my/item/awesome.epub#SomeCrazyTextRangeIdentifier
> If run on a server, it would be the server's job to extract the
> appropriate package files (when thinking about epub, the OPF for example)
> and provide that to the client, who can then determine the resources it
> needs and request them from the server.
> When run LOCALLY, the client will simply extract the package files
> directly.  Otherwise there is no duplication of work or resources, etc.
> There was a note about the fragment (things after the #) not being sent to
> the server.  If that is truly the case - and not just that the server
> ignores it - a DIFFERENT marker - what - i have no idea...
> -Nick
> On Mon, Jun 1, 2015 at 6:22 AM, Ivan Herman <ivan@w3.org> wrote:
>> Hi all,
>> my sincere apologies for the length of this mail, but I thougt it would
>> be worthwhile to get some issues written down to clarify our discussions...
>> On the F2F meeting I made the claim that the identifier/fragment issue
>> may be the most tricky one facing us around EPUB-WEB. I thought it is worth
>> writing this down; maybe somebody can also prove me wrong that this is not
>> such a complex issue after all. Actually, what is below is a summary of a
>> very short email/personal discussion Markus, Tzviya, and I had on the
>> matter after the F2F. (At some point it is probably worth writing down the
>> conclusions of this thread somewhere on the wiki.)
>> With that, here is where I see a real problem.
>> Let us consider a Packaged Document. The URL of this document is
>> http://www.example.org/doc. The document includes, among others, chapter
>> 2 in file chap2.html. This has a section whose ID is 'sec' (for the sake of
>> simplicity, I consider here the simplest and best known fragment used in an
>> HTML file, ie, using the @id attribute on a, say, <h1> element). The
>> question arising is: what is the full URI for that section? Or, to be more
>> exact, what is the full, *canonical* URI for that section, ie, a URI that
>> is independent on whether the document is off-line or on-line?
>> An Aside: How do URI-s work?
>> ----------------------------
>> Tzviya told me privately that not everyone on the group may know how
>> exactly URI-s and fragments work in browsers and on the Web. So maybe just
>> a few words may be relevant here. If you know this, my apologies, you can
>> just skip this part.
>> A URL consists of, roughly, two parts:
>> - A "primary" address that identifies the resource somewhere on the web.
>> Say, 'http://xyx.example.com/mydoc'
>> - A "fragment", that is added after the '#' sign, which identifies
>> something *within* the resource; say, 'mysection'
>> There are two steps in handling this to take into account:
>> - There can be *only one fragment id in a URL*, ie, only one occurence of
>> '#'. What is after the '#' is interpreted in accordance with a
>> corresponding specification that is bound to the media type of the resource
>> - A Web browser interprets the fragment locally. Ie, if it gets '
>> http://xyx.example.com/mydoc#mysection' it
>>         1. strips the fragment
>>         2. it issues a request, through the HTTP protocol, for '/mydoc'
>> to the 'http://xyx.example.com' server
>>         3. it gets the full resource and then uses the fragment (i.e.,
>> 'mysection') to identify something within the returned resource.
>> What is the URI with fragment for section 'sec' in a package?
>> -------------------------------------------------------------
>> (For the sake of this discussion I refer to the way the packaging
>> specification works in terms of fragments.)
>> 1. If http://www.example.org/doc refers to a real, physical package on
>> the Web, accessing 'sec' chap2.html, using the current fragment
>> specification in the packaging document, would be:
>> http://www.example.org/doc#url=/chap2.html;fragment=sec
>> meaning:
>>         1. The client retrieves the package http://www.example.org/doc
>>         2. Unpackages the package in a local cache (or equivalent)
>>         3. It interprets the fragment 'url=/chap2.html;fragment=sec' by
>> (per the current specification of packaging) by
>>                 3.1. identifying the 'part' within the package, yielding
>> 'chap2.html'
>>                 3.2. 'chap2.html' is an HTML file; because the server
>> knows how to identify something within the file with a fragment, ie, it
>> gets to section 'sec'
>> It is important to realize that, in this model, the 'unpackaging' is done
>> by the client (the browser i.e., the reading system)
>> 2. If the package is just 'virtual', ie, all documents are on the Web,
>> then there is of course a much simpler approach. The URL of the section is
>> http://www.example.org/doc/chap2.html#sec
>> meaning
>>         1. The client retrieves the HTML document
>> http://www.example.org/doc/chap2.html
>>         2. It knows how to identify something within the HTML file with a
>> fragment, ie, it gets to section 'sec'
>> Back to the original question: what is the 'canonical' URI with fragment?
>> -------------------------------------------------------------------------
>> It should be one of the two above. However, both have issues:
>> A. http://www.example.org/doc/chap2.html#sec
>> Pro: this is the 'natural', Web way.
>> Con 1: *if* the document is, in fact, a real package then there are two
>> possible approaches to handle this:
>> Con 1.1: The *server* handles the unpackaging. Ie, it should be in
>> position to analyze the URL it receives, realize that there is a 'package'
>> in between and do an unpackaging. What this would mean is that the client
>> would have to make requests for all chapters separately, which is not
>> optimal (although it can of course be cached)/
>> Con 1.2: The *client* handles unpackaging. This would require a different
>> server-client protocol, namely:
>>         1. The client issues a request to '
>> http://www.example.org/doc/chap2.html'
>>         2. The server returns 'http://www.example.org/doc/' as a package
>> instead of the original chap2.html file (ie, the server should know that
>> this is part of a package through some redirection)
>>         3. The client should then unpack and locate the chap2.html file
>> in the package
>>         4. the fragment should be identified and handled.
>> Steps 1-2-3 is not the current practice on the Web in terms of Web
>> Architecture: a client does not 'decompose' the 'primary' part of a URL
>> (beyond separating the server's identification from the part within that
>> server). It is unclear whether changing that is a viable/acceptable for the
>> browsers, and for the overal Web Architecture; it certainly requires a
>> discussion with the TAG.
>> Con 2: If the URL is, in fact, a file:///... type one, this means that,
>> for that case, the unpackaging must be done on the client. Ie, there may be
>> duplication of functionality with the server and the client, which is not
>> optimal.
>> B.  http://www.example.org/doc#url=/chap2.html;fragment=sec
>> Pro: this works for a package.
>> For a document on the Web, it may also work if there is a 'conceptual'
>> entity on the Web for the document. I.e., http://www.example.org/doc
>> returns some sort of an information to the client that this is, fact, a
>> 'virtual' package, and then the server can issue a new request to
>> http://www.example.org/doc/chap2.html and take it from there.
>> (Note that, regardless of the original issue, having a 'conceptual'
>> package handle for a document may not be a bad thing!)
>> Con: The URL form is (much) more complex, and may be in danger of being
>> ignored for documents that are on the Web only.
>> Personally, I do not have a clear solution in my head. Hence this mail,
>> trying to see how we can move on...
>> Let me also add another remark, coming originally from Tzviya, just to
>> add it to the mix: "We need to think about situations such as multiple
>> authors creating one package or peer review (one or many authors + one or
>> many editors submit article + data set to journal for review. It undergoes
>> peer review by one or many reviewers. Journal rejects the article.
>> Something happens to the reviews, and the package is submitted to a second
>> journal) and so on.) In scenarios like this, the concept of versioning and
>> revisioning are a lot more important. It may be covered by OA. I don’t know
>> that we can resolve versioning with an identifier."
>> (Again, apologies to be so verbose…)
>> Ivan
>> ----
>> Ivan Herman, W3C
>> Digital Publishing Activity Lead
>> Home: http://www.w3.org/People/Ivan/
>> mobile: +31-641044153
>> ORCID ID: http://orcid.org/0000-0003-0782-2704
> --
> - Nick Ruffilo
> @NickRuffilo
> http://Aerbook.com
> http://ZenOfTechnology.com <http://zenoftechnology.com/>
Received on Monday, 1 June 2015 14:59:31 UTC

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