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RE: Two link questions

• To: 'Gustaf Liljegren' <gustaf.liljegren@b...>, xml-dev@l...
• Subject: RE: Two link questions
• From: Eckenberger Axel <Extern.Eckenberger@k...>
• Date: Wed, 16 Jul 2003 09:48:21 +0200

Gustaf,

> I have two questions about links.
> 
> 1. The most common link pattern is the one-to-one link. If I 
> got it right, there's no need to separate one-to-many from 
> many-to-one, because that's controlled by the link's 
> direction. How about many-to-many? Do you ever need a 
> many-to-many link?

XLink specifies two link types, single and extended. 

The single link is the most common link, unidirectional from the source
document to another document. 

The extended link offers a bit (slight understatement :-) ) more
flexibility. It allows the author to define multiple locations (i.e.
sections of the sourcedocument specified by an Xpointer expression) and
resources (i.e. hrefs to another resource in the web - documents,
web-services, functions, etc.). Furthermore, it allows the author to specify
any unidirectional link (i.e. an arc) between the locations and resources.

This allows to build up database like relations between the locations and
resources and, like in databases, it depends on the application which links
are sensible and which are not. A sample for a many to many link migt be a
network of information items (e.g. documents) which shows the
interdependence of the items.

 multiple unidirectional links from a internal (within the source document
and specified by an XPointer expression) or external (within or outside the
document and specified by a href). The multiple unidirectional links (i.e.
the arcs) can form in their sum 1:1, 1:n, and m:n links.

> 2. I'd like to know more about link-bases, but it seem so 
> elusive and XLink doesn't say much about it. Is there a good 
> place to start?

Linkbases are basically just a list of extended links that are held in a
separate document and where the ling source and link targed do not know
anything about the fact that they are linked together. I agree with you that
the spec does not say much about it, especially as there is a problem
locating the link base that is relevant for a given document. On the other
side linkbases have a great potential to deliver a exchangable context under
which a relation between resources is viewed.

Axel

If you are interested there is a presentation at htt://www.metalogic.de
(Info/Download - Samples und Präsentationen) which I held at the XML-ONE
2001 in Munich, sadly it's in German :-)

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