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RE: URIs and Named Graphs

From: Hans Teijgeler <hans.teijgeler@quicknet.nl>
Date: Sun, 8 Jul 2007 09:46:11 +0200
To: "'Alan Ruttenberg'" <alanr@mumble.net>
Cc: "'SW-forum'" <semantic-web@w3.org>, "'Paap, Onno'" <onno.paap@gmail.com>, "Benjamins, Robin" <rxbenjam@bechtel.com>
Message-ID: <000001c7c134$118b4af0$6c7ba8c0@hans>

Hi Alan,

Of course I want to answer your questions!
I'll respond below.

Thanks for your help!
Hans 

-----Original Message-----
From: Alan Ruttenberg [mailto:alanr@mumble.net] 
Sent: Sunday, July 08, 2007 0:05
To: Hans Teijgeler
Cc: SW-forum; Paap, Onno
Subject: Re: URIs and Named Graphs

Hello Hans,

I'm trying to understand your scenario, and have some questions.

- Why would you have hundreds of quad stores instead of a single larger quad
store with more qualifications on the queries?
<HT> That has to do with data ownership. On a project we have a hierarchy of
data consolidation and integration, from many individual applications (e.g.
process simulation, stress analysis, pump sizing) via the responsible
discipline group on a project (e.g. Process Engineering) to the
consolidating project store, and then to the quad store of the plant
owner/operator. The latter may have many projects underway, and all projects
use and produce data that needs to be integrated. These apps, disciplines
and (sub)projects often are spread around the globe.
The data at a lower level in the hierarchy are usually not accessible to the
higher levels, because they are "work in progress" and should not be used by
anybody else. Data, and their custodianship, can be "handed over" to the
next level of consolidation. That hand-over involves a physical relocation
from one quad store to another. The URI changes, the fragment identifier
stays the same or gets a suffix, separated by a middle dot (00B7). We keep
track of that location by storing that in, you guessed it, a partition
"redirects" (one of the nine).
One other reason for the many quad stores is the situation that the
suppliers on a project (often in the hundreds) need to share their data with
many other customers.

- What motivates the uses if URI#fragIDs in the first place?
<HT> Our data model is close to 5NF, very generic and fine-grained. On a
refinery we have zillions of physical objects that all have their lifetime
information recorded. Any chunk of information is attributed to a "temporal
part" of the object involved, so we have zillions of objects with zillions
of temporal parts.

- SPARQL allows queries that span multiple named graphs - why would you need
to have different end points for the different partitions, which I
understand to be equivalent to named graphs?
<HT> I don't know whether or not that is equivalent. If we have the
partition "sent messages" we will have many triples in it, forming many
graphs that may or may not have any connection to other graphs in that same
partition. But all triples will have a URI for "sent messages" as their 4th
column. Would you still call that named graph?
I will ask Onno Paap (on cc), our "head techie", to respond on your "SPARQL
vs multiple named graphs" remark. That is out of my league :-(

- What would you expect the behavior to be for something like
URI#partition#fragID? The only behavior I am aware of for hashes is in the
context of http GET, where only the URI before the hash is sent as the
target of the GET. Do you depend on this behavior already? If so, to
accomplish what?
<HT> No, I was just wondering how we can fetch a particular fragment ID from
a particular "partition", and then dereference it.

- What do browsers have to do with the scenario?
<HT> Not much, only indirectly, granted.

You might not want to answer these questions - in that case consider them as
an indication of whether you are adequately communicating your problem to an
audience familiar with SW technologies, as I consider myself to be.
<HT> I hope I have improved on my communication skills :-)

Regards,
Alan


On Jul 5, 2007, at 7:57 AM, 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
> hans.teijgeler@quicknet.nl
>
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Received on Sunday, 8 July 2007 07:47:29 UTC

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