RE: [xml-dev] Xlink Isn't Dead

["Michael Kay" <mike@saxonica.com>]

> 
>          If a styling language were able to say "this is a 
> link" and "that attribute is the link address" and other such 
> goodness, what else would be needed in core XML?

Look at what we've got:

parent/child relationships: fine so long as the data is hierarchic

ID/IDREF, with strange lexical rules on the form of an identifier, with no
ability to have more than one domain of identifiers in the same document,
with no ability to say what kind of thing an IDREF is supposed to identify,
and which is confined in scope to a single document.

key/keyref in XML Schema, which removes many of the constraints of ID/IDREF
but which is still, crucially, confined to intra-document relationships (and
whose specification is incomprehensible to mortals)

URIs, which mean anything you want them to mean: a semantic-free zone, but
one with ugly syntactic constraints

RDF, which is impractical for most applications and bears very little
relationship to XML.

What's needed is a mechanism for declaring and maintaining non-hierarchic
relationships between objects (elements) that allows:

* freedom of choice in the syntactic form of the identifier

* freedom of choice in the naming of identifiers 

* independence of document boundaries

* indirection between identifiers of objects and the addresses of the
documents containing them 

* indirection between identifiers of objects and their XML representations

* bi-directional (inverse) relationships

* flexibility in the management of referential integrity

* versioning

etc.

Michael Kay
http://www.saxonica.com/