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Re: Follow up on our conference call on 7/11...

From: Kingsley Idehen <kidehen@openlinksw.com>
Date: Thu, 17 Jul 2008 14:24:17 -0400
Message-ID: <487F8E51.30009@openlinksw.com>
To: ashok.malhotra@oracle.com
CC: "Ezzat, Ahmed" <Ahmed.Ezzat@hp.com>, "public-xg-rdb2rdf@w3.org" <public-xg-rdb2rdf@w3.org>

ashok malhotra wrote:
>
> Hello Ahmed:
> Thank you for starting this thread.
>
> In my view, there are situations where you want to translate the data 
> to RDF and then store it and query it
> but, if the data is very large and/or changes frequently a better 
> approach is to leave the data in the native
> database and create a virtual RDF representation for it -- which I 
> call a semantic cover. The semantic
> cover can then be queried with SPARQL and the SPARQL queries 
> translated to queries over the native
> databases.
For sake of clarification etc.

What Ashok calls a "Semantic Cover" is exactly the same as what describe 
as an "RDF View".  As you can see, we are both using different labels 
for an identical concept: Data Views.

Views have been an intrinsic part of Database Technology since the 
beginning of time, they may be transient or full materialized. Thus, you 
can look at this whole realm of RDB to RDF (or SQL to RDF) as an 
exercise in Data View generation.

Warehouses are fully materilized Views.
>
> It should also be possible to enrich the semantic cover with 
> additional semantics but exactly how this would
> be done needs to be worked out.
>
In a consensus sense yes. But this is something we've implemented in 
Virtuoso base on our world view of this subject matter.
> A recommendation that our XG may want to make to the W3C is to start 
> work on a language that would map
> relational data to RDF. The mapping may be used to translate the data 
> to RDF and store it in a RDF database
> or it could be used to create a virtual mapping as discussed above.
>
> We have heard a number of presentations on quick default mappings of 
> Relational data to RDF. But we also
> need the ability to customize these mappings and add additional 
> semantics.
>
> This approach starts with the Relational database schema. An 
> alternative approach may be to create an ontology
> first and then create (distributed) SQL queries to answer questions 
> about the ontologies.
>
> Ahmed, does that cover what you had in mind?
>
> All, please respond to this note so we can start coming to a shared 
> understanding as to what we should
> recommend to the W3C.

Made my contribution :-)

Kingsley
>
> All the best, Ashok
>
>
> Ezzat, Ahmed wrote:
>> Hello,
>> This is a question that I would be interested in hearing your 
>> reaction and views about.
>> In a multiple data sources environment where some of them are huge 
>> like data warehouses, it seems like transforming all data sources 
>> into RDF then querying that RDF store using SPARQL is going to put 
>> too much pressure on the RDF store beyond reasonable. In addition all 
>> changes in these data sources need to be reflected in the RDF store 
>> as soon as possible. In the above paragraph I am ignoring the notion 
>> of local and domain Ontologies.
>> An alternative I am exploring is to decompose the user query into set 
>> of subqueries (SQL and Search) operations to the relevant data 
>> sources (i.e., context) ŕ transform the results into RDF using local 
>> Ontologies then resolve differences using the domain ontology ŕ apply 
>> the SPARQL query on the union of the RDF graphs after reconciliation. 
>> Even this approach is far better from RDF storage point of view 
>> (i.e., scalability), it seems like response time can be less than 
>> desirable?
>> Comments and thoughts including additional alternatives…
>> Regards,
>> Ahmed
>> /*Ahmed K. Ezzat, Ph.D.*//* */
>> *HP Fellow*, *Business Intelligence Software Division
>> **Hewlett-Packard Corporation** *
>> 19333 Vallco Parkway, MS 4502, Cupertino, CA 95014-2599*
>> **Office*: *Email*: _Ahmed.Ezzat@hp.com_ <mailto:Ahmed.Ezzat@hp.com> 
>> *Tel*: 408-285-6022 *Fax*: 408-285-1430
>> *Personal*: *Email*: _AhmedEzzat@aol.com_ <mailto:AhmedEzzat@aol.com> 
>> *Tel*: 408-253-5062 *Fax*: 408-253-6271
>>
>> ------------------------------------------------------------------------
>>
>
>


-- 


Regards,

Kingsley Idehen	      Weblog: http://www.openlinksw.com/blog/~kidehen
President & CEO 
OpenLink Software     Web: http://www.openlinksw.com
Received on Thursday, 17 July 2008 18:25:01 GMT

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