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Re: /site-meta Support for URI-mapped Links

From: Alphonse Tan <alphonse.tan@gmail.com>
Date: Sun, 30 Nov 2008 09:56:47 +0800
Message-ID: <209322380811291756w396b1cd9v9060ef3f906c5bfe@mail.gmail.com>
To: www-talk@w3.org
Eran:

Gud day to you, i am just a self-learned web designer/web developer. i've
been up to my neck studying and trying to fit in w3 standards. But i can't
seem to catch up.

Question is where do i get, aside from w3.org(sorry guys), get some
standards just like what you outlined, readable in plain english. Not that I
am slow to understand, just that plain english guidelines more or less takes
out the chances of me thinking of something else..

Thanks and more power.

Alphonse
http://www.etnmultimedia.com


On Sun, Nov 30, 2008 at 9:36 AM, Eran Hammer-Lahav <hueniverse@gmail.com>wrote:

> A Bit of Background
>
> My involvement in the /site-meta proposal came directly out of my work on
> web discovery [1]. This goal is to provide a uniform and easily
> implementable method for locating resource descriptors.
>
> With the development of interoperability specifications comes the need to
> enable compliant services and resources to declare their conformance to
> these specifications. There is a growing need to describe resources in a
> way
> that does not depend on their internal structure (i.e. HTML, ATOM, XML,
> etc.) or even the availability of an HTTP-accessible representation of
> these
> resources served by an HTTP server).
>
> XRDS/XRD and POWDER are two descriptor formats, and OAuth, OpenID,
> OpenSocial, PortableContacts are some specifications with such discovery
> needs.
>
> ---
>
> After a long review [1] of the available methods for attaching descriptors
> to resources, three methods were identified as part of the solution:
>
> 1. <Link> Element in HTML, XHTML, ATOM, and other XML-based schemas with
> support for an equivalent element. Solves HTML/ATOM regardless of transport
> (which is still likely to be HTTP).
>
> 2. HTTP Link response-header [2]. Solves HTTP URIs with an HTTP
> representation available (if the resource is not HTTP-resolvable, it
> doesn't
> matter that the URI uses the HTTP scheme - there is no place to put the
> header).
>
> 3. Template-based mapping from the resource URI to the descriptor URI.
> Applicable to any URI scheme - basically the catch-all solution.
>
> In order to implement the URI-mapping method, we need to define (1) a
> vocabulary to deconstruct the resource URI, (2) a template format to
> construct the descriptor URI, (3) a filtering method to apply templates to
> specific URI schemes, and (4) a place to store these maps.
>
>
> Main Questions
>
> 1. Is /site-meta the correct location for storing such maps?
>
> * The main reason for the existence of these maps is that they describe the
> location (links) of resources without access to HTTP header (404 or
> non-http
> URIs), or where performance prohibit the inclusion of Link headers
> (http://yahoo.com<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2fyahoo.com>,
> http://google.com<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2fgoogle.com>
> ).
>
> * The maps define a site-wide link which is applied at an individual
> resource level, but is clearly related to the 'web site' as a whole.
>
> * The map can be viewed as a Link relationship where the 'href' attribute
> is
> replaced with a 'template' attribute which is used to constructed a Link
> for
> any given URI within that authority space (which is described by the
> /site-meta document).
>
> * If /site-meta is note the right place, it calls for /site-meta to link to
> another document which will include these maps. This of course require the
> definition of a new rel type and a new content type for the document
> listing
> the maps.
>
> * DNS has been suggested as an alternative location. A DNS approach suffers
> mainly form complexity and security (lack of DNS-SEC deployment).
>
> 2. If /site-meta is simplified to a text format with a list of Link headers
> (without the 'Link: ' prefix), how can such URI maps be included?
>
> * The original (unpublished) proposal included a new XML element next to
> <meta> called <resource-map> which will replace the 'href' attribute with
> 'template' attribute where the map is stored.
>
> * With the new proposed format [3] for /site-meta, there is no longer an
> 'href' attribute. Instead, the linked URI is listed as the first record in
> each line. Since there is not URI defined for maps, it is not clear how the
> new format can accommodate this in a clean way (start with a space? Include
> only key="value"; pairs?).
>
> 3. How rich should the common vocabulary for deconstructing and
> reconstructing the resource URI into the descriptor URI be?
>
> * The simplest proposal includes a single 'uri' variable which can be used
> in a template with a prefix/suffix combination:
>
>     http://meta.example.net?resource={uri}<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2fmeta.example.net%3fresource%3d%7buri%7d>
>
> * A richer proposal includes 'uri' and all the terms listed in RFC 3986
> [4]:
>
>          foo://example.com:8042/over/there?name=ferret#nose
>          \_/   \______________/\_________/ \_________/ \__/
>           |           |            |            |        |
>        scheme     authority       path        query   fragment
>
> where authority can be further broken down into 'domain' and 'port'.
>
> * An even richer approach includes custom support for mailto URIs:
>
>     scheme:user@domain
>
> * Going nuts can include breaking the query into a list of key/value pairs,
> breaking the path into a list of path components ('/' separated), etc.
> There
> seems to be agreement that this is going too far.
>
> 4. Which URI Templates format to use?
>
> * Current IETF I-D draft [5] for URI templates has expired with very little
> community support or indication of changes from the authors.
>
> * A simpler (but still complex) straw man proposal [6] was posted to the
> URI
> list by R. Fielding but has not been submitted as a draft at this point.
>
> * For the majority of use cases using the above vocabulary (list variables
> excluded - i.e. No going nuts), all that is needed is a simple variable
> substitution mechanism (using {}) and some way to indicate whether a
> variable should or should not be percent encoded. A simple format can look
> like this:
>
>     Resource URI: http://example.com/resource<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2fexample.com%2fresource>
>     Template: http://meta.{domain}/map?{%uri}<https://mail.ex1.secureserver.net/owa/UrlBlockedError.aspx>
>     Descriptor URI:
> http://meta.example.com/map?http%3A%2F%2Fexample.net%2Fresource<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2fmeta.example.com%2fmap%3fhttp%253A%252F%252Fexample.net%252Fresource>
>
> Variables prefixed with '%' are percent-encoded before inserted into the
> template. The other proposals posted defines that all variables are percent
> encoded by default and left unchanged if prefixed by '+'. There is no real
> difference between the two approached.
>
> * An even simpler (but ugly) approach to the above example is define an
> encoded and unecoded variable for each term (i.e. 'uri' and 'encoded-uri').
>
> 5. To what level should the map be filtered or assigned to a subset of URIs
> under the same authority?
>
> * There are generally two kinds of filters that can be applied to URI maps.
> One is based on the URI scheme and is required for proper support for
> mapping both http and mailto URIs (an important use-case in the identity
> world, such as OpenID). This is due to the different vocabulary used for
> each scheme.
>
> * The other filter is based on the value of the path and potentially query
> parts. This seems as an overkill for the currently known use-cases. The
> assumption is that if there is such a need to provide descriptors to such
> complex use cases, these resources should either be separated into sub
> domains (each with a separate /site-meta document), or all maps should use
> just the 'uri' variable and use a CGI script to redirect to the proper
> descriptor.
>
>
> Proposal
>
> Include direct support for URI-maps in /site-meta. Use a Link record
> without
> the URI (basically a record with only key="value"; pairs) with two
> additional parameters: 'template' (to hold the URI template) and 'scheme'
> (to hold the optional scheme filter).
>
> The URI template will use a simple {} variable substitution with '+' prefix
> indicating that no percent encoding should be performed. The proposed
> vocabulary includes: uri, scheme, authority, domain, port, path, query,
> fragment, and username (for mailto URIs).
>
>
> EHL
>
> [1] http://www.hueniverse.com/hueniverse/2008/09/discovery-and-h.html<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2fwww.hueniverse.com%2fhueniverse%2f2008%2f09%2fdiscovery-and-h.html>
> [2] http://tools.ietf.org/html/draft-nottingham-http-link-header-02<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2ftools.ietf.org%2fhtml%2fdraft-nottingham-http-link-header-02>
> [3] http://lists.w3.org/Archives/Public/www-talk/2008NovDec/0002.html<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2flists.w3.org%2fArchives%2fPublic%2fwww-talk%2f2008NovDec%2f0002.html>
> [4] http://tools.ietf.org/html/rfc3986#section-3<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2ftools.ietf.org%2fhtml%2frfc3986%23section-3>
> [5] http://tools.ietf.org/html/draft-gregorio-uritemplate-03<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2ftools.ietf.org%2fhtml%2fdraft-gregorio-uritemplate-03>
> [6] http://lists.w3.org/Archives/Public/uri/2008Sep/0007.html<https://mail.ex1.secureserver.net/owa/redir.aspx?C=cc75fe81921d457583420bebbbebfc13&URL=http%3a%2f%2flists.w3.org%2fArchives%2fPublic%2furi%2f2008Sep%2f0007.html>
>
Received on Sunday, 30 November 2008 07:43:46 GMT

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