RE: comparing XML and RDF data models

In my opinion:

If you wish to query, without knowing the content in advance, then you
need a language like OWL (http://www.w3.org/TR/owl-guide/), where
entries have the capability to explain themselves and how they relate to
other entries.
SPARQL & RDF will fail on that as you still need to know what the
relations are by name (you must be aware of hasName and hasSensor in
your example before being able to query).

Cfr http://jowl.ontologyonline.org/
David Decraene.

-----Original Message-----
From: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org]
On Behalf Of Maciej Gawinecki
Sent: dinsdag 1 juli 2008 12:21
To: semantic-web@w3.org
Subject: comparing XML and RDF data models


In one of the article comparing two data models: XML and RDF I found a 
statement stating that (I'm loosely citing from my memory):

   Searching XML with XPath query expression is easy if you know the
   schema of the document being quiried. However, the same query will
not
   work any a document, which is differently structured, but contains
   equivalent information. This can be solved by usage of RDF model,
   which can be then queried with RDQL or SPARQL query.

Is that really true, that XPath-based XML search is limited due to its 
structure? Yes, that's why there is a great research on keyword-based 
quering of XML documents (not knowing schema in advance). But is it RDF 
really better for this issue ?

I will try to give a few example what I exactly mean. [Of course, I'm 
ommiting here the problem of knowning the name a tag/property/resource, 
only the structure can be different.] Let's see two XML documents:

   <Sensor>
     <name>Sensor220</name>
     <isLocatedNearBy>
       <Road>
         E330
       </Road>
     <isLocatedNearBy>
   </Sensor>

Here road value can be check through XPath expression: 
\\Sensor\isLocatedNearBy\Road

And let's see differently structured document (road defined by name 
property)

   <Sensor>
     <name>Sensor220</name>
     <isLocatedNearBy>
       <Road>
         <name>E330</name>
       </Road>
     <isLocatedNearBy>
   </Sensor>

With XPath expression: \\Sensor\isLocatedNearBy\Road\name

Or yet another one (road is ancestor tag to the sensor tag, not the
oposite)

   <Road>
     <name>E330</name>
     <hasSensor>
       <Sensor>
         <name>Sensor 220</name>
       </Sensor>
     </hasSensor>
   </Road>

XPath: \\Road\name

The same problem would be with RDF. Let see the first model

   :Sensor220 :isLocatedNearBy :Road_E330 .

WHERE clause of SPARQL query would be then like a

   ?s :isLocatedNearBy :Road_E330 .

For other version we define a road with a specific value of hasName 
property:

   :Sensor220 :isLocatedNearBy :RoadXXX .
   :RoadXXX :hasName "E330" .

the SPARQL query part:

   ?s :isLocatedNearBy ?r .
   ?r :hasName "E330" .

or by analogy to the third XML representation (road "has" a sensor, not 
the opposite):

   :RoadXXX :hasName "E330" .
   :RoadXXX :hasSensor :Sensor220 .

the SPARQL query part:

   ?r :hasName "E330" .
   ?r :hasSensor ?s .

Can someone comment it ?

Thanks,
Maciej

Received on Tuesday, 1 July 2008 10:51:24 UTC