Re: DOCBOOK: Linking in DocBook (specifically for EBNF, but more generally as well)

[Terry Allen <tallen@sonic.net>]

Thanks, Eve.
| >Anyway, what is its relation to
| >Xlink?
| 
| XLink is an XML vocabulary that allows XML documents to contain 
| "standardized" linking markup.  It can be useful if recognized as-is by 
| browsers, but a lot of the time it is likely to be used in the formulation 
| of a higher-level language that has some linking in it.  You can think of 
| it, inaccurately, as letting XML documents "link to" other things.  (It's 
| inaccurate because some XLink links don't link the document they're in to 
| something else; they link remote things together.)  XLink links can 
| associate non-XML resources, even though the linking elements themselves 
| are always in an XML document.

So use of an xlink: attribute specifies the semantics of the link
but not the syntax?

| XPointer is a non-XML mini-language that gets used as fragment identifiers 
| on URIs, when the URI refers to something with an XML (text/xml or 
| application/xml) media type.  It is specifically designed to be extensible 
| and useful for other XML-based media types if they want to use it in 
| defining their own fragment ID languages.  XPointers can appear in non-XML 
| resources (e.g., HTML), even though they always address into an XML document.

Which is not to say you can't use another method, if you define it
and don't use URLs.  (Note that the URN WG did not agree that fragment
identifiers made sense with URNs, so there is no provision for them.)
Not that I'm suggesting it; the point is that the semantics of the
fragment ID are bound to the media type of the target, so you can't
make up your own syntax for fragment IDs (although queries are fair
game ...).

| >"#foo" doesn't seem like a shortcut to me, as it's relative-URL
| >syntax.  So now I'm worried.  Can you tell me where in the Xpointer
| >spec the proposed syntax is defined?
| 
| Actually, it's not related to whether a URL is relative.  Here's how things 
| break down:

"#foo" alone would be relative to the current document (whatever
that will end up meaning).

| As I think Norm has pointed out, the HTML #foo and the XPointer #foo aren't 
| exactly alike.  (This is actually discussed a bit in the spec itself.)  But 
| #foo in XPointer is exactly identical to IDREF.

I think I've got it now.  But I'd like to switch over consistently
throughout the DTD, and when tool support is ready.

regards, Terry