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Re: URIs and Named Graphs

From: Ioachim Drugus <sw@semanticsoft.net>
Date: Thu, 05 Jul 2007 11:24:10 -0700
Message-ID: <468D374A.1030204@semanticsoft.net>
To: Hans Teijgeler <hans.teijgeler@quicknet.nl>
CC: SW-forum <semantic-web@w3.org>, "Paap, Onno" <onno.paap@gmail.com>

Hi Hans,

I don't know about a generally accepted approach, but I will share how our group deals with this.

We focused on URLs and URNs as separate *identification spaces* within the URI identification space.
The URL space consists of *identities*, which do not need a context to identify (one-to-one) a resource. 
They are "context-free" with respect to identification

The URN space consists of *identifiers*, which make *abstraction* from the context and, 
in order to serve as *identities* they need a context.

Now, both spaces are governed by their relationships of order and the paths are denoted different manners. 
The paths in URL space are built by using "/". They usually do not talk about *paths* in URN - a URN is
defined as urn:NID:NSS, where NID is the Namespace ID and NSS is Namespace Specific 
String, or to put it simpler *urn:namespace:name*

The syntax does not allow to use a column within the namespace. But it says nothing about this regarding the name.
Based on this, we build urn names like  this - *urn:reality:domain:object:partition:fragment* 
And so, in the URN space you can also have *paths*.

Now, the only thing which remains is to define a *mapping* of the URN space into URI space which also "contextualize"
URNs with a base URL. We just "throw away" urn: prefix and replace everywhere the column with "/". 
Mapping can be defined different manners, but this mapping is good when you need to 
put into one directory all the software objects namespaced by the name of the directory.

Now, our idea about software which works with URIs, is that it should
use only URNs and only when "publishing on the web" they map URNs to URLs.

As to #, it serves for "attaching leaves" to a tree and a "leaf" cannot 
have branches. Therefore, I doubt that the standards will allow multiple 
# within one URI

Ioachim Drugus
Main Architect,
Semantic Soft

Hans Teijgeler wrote:
> Hi,
> We ran into a problem for which I ask advice from this esteemed forum.
> First some background information: we use the SW technologies in 
> conjunction with a generic data model to create a distributed data 
> base for each engineering project, involving large numbers (in the 
> hundreds) of quad stores per project.
> To give an example of using a data model "underneath" OWL: normally 
> you may see things like an <owl:Class rdf:ID="Car"/>.
> For us that would be: <part2:ClassOfInanimatePhysicalObject 
> rdf:ID="Car"/> where ClassOfInanimatePhysicalObject is an entity type 
> in our data model and an owl:Class.
> If an application has data that must be shared, that data is mapped at 
> the source from its proprietary format to ISO 15926-7 format, and 
> stored in a quad store that we call a "Fašade".
> Only "owned" data are stored, other data a fetched with SPARQL for 
> other Fašades.
> Data can be "handed over" to another Fašade, thus also handing over 
> custody for that data.
> Quad stores that participate in a given project are known to a "CPF" 
> server (Confederation of Participating Fašades), where we distrubute 
> SPARQL queries, consolidate query results, whilst controling access 
> rights.
> For the Fašades we use RAP, and want to use the 4th column of 
> their Named Graphs for dividing the quad store into partitions 
> like 'active data', 'archive', and the like. Actually we have nine 
> such partitions, but I won't annoy you with the details.
> We use URI#fragID's all over the place.
> The question is how we can dereference any such fragment identifiers 
> inside a particular partition without having to have nine endpoints 
> (which is costly and harder to manage).
> It would be nice if we could use composite fragment identifiers like 
> URI#partition#fragID, but the second hash # would not be allowed. If 
> we would use something like URI#partition__fragID that would be 
> well-formed, but hardly usable with generic browsers (I guess).
> Please shed some light on this.
> Regards,
> Hans
> ____________________
> OntoConsult
> Hans Teijgeler
> ISO 15926 specialist
> Netherlands
> +31-72-509 2005
> www.InfowebML.ws <blocked::http://www.infowebml.ws/>
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Received on Thursday, 5 July 2007 18:24:18 UTC

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