MURATA Makoto | 1 Jun 08:52 1999

Re: Media types, fragment identifiers, and XPointer

I was expecting more response, but only Larry responded ;-)
#Thanks.  > Larry

Larry Masinter wrote:
> It would be good if we could extend the MIME registry of media
> types to include, where possibly, a description of how
> "fragment identifiers" apply to that media type.
> Currently this information is not in the media type registry,
> and fragment identifiers are, in practice, only used for HTML.

RFC2396 ("Uniform Resource Identifiers (URI): Generic Syntax"), which 
you co-authored, says:

   The semantics of a fragment identifier is a property of the data
   resulting from a retrieval action, regardless of the type of URI used
   in the reference.  Therefore, the format and interpretation of
   fragment identifiers is dependent on the media type [RFC2046] of the
   retrieval result.  The character restrictions described in Section 2
   for URI also apply to the fragment in a URI-reference.  Individual
   media types may define additional restrictions or structure within
   the fragment for specifying different types of "partial views" that
   can be identified within that media type.

   A fragment identifier is only meaningful when a URI reference is
   intended for retrieval and the result of that retrieval is a document
   for which the identified fragment is consistently defined.

text/html is defined by RFC1866 (HTML 2.0).  HTML 2.0 and its subsequent 
(Continue reading)

Chris Lilley | 1 Jun 13:57 1999

Re: Media types, fragment identifiers, and XPointer

MURATA Makoto wrote:

> Q1.  Do we need XPointers for every XML instance?

They should be available, even if that capability is not used by a
particular instance. Other instances may point to that instance, and
will use XPointer to do so.

A particular xml document type might not use XPointer itself,
internally, but other people linking to parts of that document might
well expect XPointers which *they* make to that document type, to work.

> I personally think that this is too much.  For example, I do not think we have
> use XPointers for RDF, which is in the XML syntax.

It is arguable that a later, refined syntax for RDF should use XPointer,
for compatibility with other XML applications.

> Q2.  Do we need XPointers only for human-readable documents that are rendered
>      by some browsers?
> I am not sure if the answer is Yes.  How do XLL experts in this ML feel?

SVG (which is human viewable, though non-viewing applicationsa re also
possible) uses XPointer and XLink for such things as referencing
graphical symbols, which are to be re-used, or for pointing to runs of
text which are to be presented graphically (for example, as text on a
curved path).
(Continue reading)

John Cowan | 1 Jun 16:52 1999

Re: Media types, fragment identifiers, and XPointer

Chris Lilley wrote:
> It is arguable that a later, refined syntax for RDF should use XPointer,
> for compatibility with other XML applications.

As currently defined, RDF uses bare ID values, which is a degenerate
form of XPointer that the (current) XLink WD blesses.


John Cowan		cowan <at>
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

Simon St.Laurent | 2 Jun 16:36 1999

Re: Media types, fragment identifiers, and XPointer

At 10:57 AM 5/28/99 +0900, MURATA Makoto wrote:
>It appears that media types, fragment identifiers, and XPointer are 
>actually related.

This is an important question that operates on several levels.  Fragment
identifiers (and supporting linking mechanisms) are a 'generic' tool that
can be used with any XML document.  On the other hand, not all applications
using XML will support fragment identifier processing.  XLink (ancient but
current draft, 3/98) suggests that regular #xxx identifiers be processed on
the client, and gives a query syntax for getting the fragment from the
server, but this infrastructure seems inadequate.

>XPointer is intended to be used as a fragment identifier.
>	"The locator for a resource is typically provided by means of a 
>	Uniform Resource Identifier, or URI. XPointers can be used as fragment 
>	identifiers in conjunction with the URI structure to specify a more precise 
>	sub-resource."
>I personally have expected that XPointer is usable for every XML document 
>no matter what the media type is.  But I am apparently wrong.  Do we need 
>a top-level media type "xml" or some convention such as "image/xml.vml" 
>so that XPointer can be used for any XML document?  Or, are "text/xml" and 
>"application/xml" enough?

XPointer should be usable for every document that is a well-formed XML
document, whatever the media type.  However, software is going to need to
know that the document is indeed XML to know how to interpret the
XPointer...  XPointer is an excellent example of a generic XML tool that
works with any XML document in a wide variety of of different situations.
(Continue reading)