W3C home > Mailing lists > Public > public-owl-wg@w3.org > December 2007

imports and absolute URIs

From: Jeremy Carroll <jjc@hpl.hp.com>
Date: Fri, 21 Dec 2007 16:08:23 +0000
Message-ID: <476BE4F7.5090703@hpl.hp.com>
To: "Web Ontology Language ((OWL)) Working Group WG" <public-owl-wg@w3.org>


I keep running the following analogy in my head, and it doesn't quite 
work, which does show that the imports issue has a little more content 
than I have been making out ...

Analogy
=======

Xiao-Wei wants to publish a Web page in HTML, with a picture of his 
family, as a PNG image.

He gets out his camera and takes the photo, transfers the image to his 
PC, converts the format.

He then starts up his text editor, writes his html page, and adds
   <img src="family.png">
and looks at the page in his Web browser (looking at #
file://localhost/tmp/mypage.html
)
when he is satisfied he uploads both files (the HTML file, and the PNG 
file) to a Web server,at example.org, and everything works (looking at
http://www.example.org/xiao-wei/mypage.html
)

He does the same with his ontology files, and it doesn't work.

Returning to the HTML, PNG files,
example.org start to recommend that he uses the html base element to 
declare a base URI for his HTML files. He does this, and he finds that 
his previous edit/preview cycle stops working, because the preview of 
the local HTML file uses the image file from the Web, rather than from 
his local machine.

-----

Carefully thinking through when the ontology edit/upload stops working, 
it is with the addition of an xml:base, or when we refer to an entity 
defined in one of the ontologies using an absolute URI (typical through 
a namespace).

This is required (rather than using local URIs) because of the decision 
that XML Namespaces must be absolute URIs and not local ones.

Which is the topic of another current thread
see e.g.

http://lists.w3.org/Archives/Public/semantic-web/2007Dec/0117

====

There is a mess here, in how to move a group of files that reference 
each other using absolute references from location A to location B on 
the web.

OWL imports is an instance of this problem, because while the imports 
can and should be done using relative refs, at various points absolute 
references are needed.

I don't believe we should be solving that problem in this group.

I think a good practice, for low-tech tools, would be to have near the 
top of each of the files a single XML entity definition that gives the 
'top' of the logical hierarchy. As you move the docs around, you would 
need to change that.

I would expect many tools would want to be more sophisticated.


Jeremy
Received on Friday, 21 December 2007 16:09:00 GMT

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