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Re: RDF vs. relational databases

From: Chris Bizer <bizer@zedat.fu-berlin.de>
Date: Tue, 29 Aug 2006 18:43:16 +0200
Message-ID: <002501c6cb8a$3a49fa90$83ec2da0@named4gc1asnuj>
To: Sören Auer <auer@informatik.uni-leipzig.de>, <semantic_web@googlegroups.com>
Cc: "revi s." <reviswami78@yahoo.com>, <www-rdf-interest@w3.org>

My to cents.

I completely agree with Sören, that one strength of the RDF data model is 
its flexibility.

Two things that appear at least equality important to me and that are not 
provided by the relational model are globally unique identifiers and links.

By using globally unique identifiers, everybody can add information about a 
resource. By using links, you can refer from your resource to somebody 
else's resource. Meaning that you can set a link from one database 
(repository) to another, which clearly isn't possible with classical 
relational database technology.

Tim's tabulator browser [1] shows nicely how these links can be followed by 
using URI dereferencing and the good old rdf:seeAlso property. I also like 
Bastian's work on federated SPARQL queries [2], which shows how globally 
unique identifiers enable queries over multiple data sources. So the 
Semantic Web community is getting closer to having the access paradigms of 
the classical web - browse and search - also work for the Semantic Web.

Thus, I think where the RDF model really starts playing it strengths is data 
integration and data linkage. We are currently exploring data linkage in the 
context of D2R Server [3] , a tool for publishing the content of classical 
relational databases on the Web. D2R Server allows you to query relational 
databases with SPARQL. Currently, we are extending the server with URI 
dereferencing features, meaning that you can retrieve RDF representations of 
the objects in your relational database. This will allow you to set links 
between different relational databases, allow you to refer from your webpage 
or blog to an object within a relational database or use a tool like 
Tabulator to transparently browse from the content of one relational 
database to the content of another.

So my guess: If RDF is good for something, it is good for data integration 
and data linkage.



[1] http://www.w3.org/2005/ajar/About.html
[2] http://darq.sourceforge.net/
[3] http://www.wiwiss.fu-berlin.de/suhl/bizer/d2r-server/

----- Original Message ----- 
From: "Sören Auer" <auer@informatik.uni-leipzig.de>
To: <semantic_web@googlegroups.com>
Cc: "revi s." <reviswami78@yahoo.com>; <www-rdf-interest@w3.org>
Sent: Tuesday, August 29, 2006 4:39 PM
Subject: Re: RDF vs. relational databases

 From my point of view (next to the distribution aspect) flexibility is
a crucial difference between the RDF based Semantic Web representation
techniques and databases:

With databases schema changes are very time consuming operations - the
whole repository and keys have to be reorganized. Triple stores on the
contrary don't distinguish between data changes and ontology schema
changes - both are finally just additions or deletions of triples.
However, triple stores will probably never be able to compete with
optimized database schemas with respect to query speed. So if you need
high speed querying and you don't expect many schema changes use a
RDBMS, if you want to be very flexible with your schema/ontology use a
triple store. The RDF paradigm is also a bit more holistic in the sense
that everything from data, schema to metadata is encoded in triples,
while databases usually have different encoding techniques for each of


Received on Tuesday, 29 August 2006 16:43:29 UTC

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