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Some SPARQL Tests on the proposed DR model

From: Phil Archer <parcher@icra.org>
Date: Mon, 26 Nov 2007 15:45:27 +0000
Message-ID: <474AEA17.9070004@icra.org>
To: Public POWDER <public-powderwg@w3.org>

Following on from the discussion on this list today, I thought I'd try 
and do some more due diligence by running some tests against some sample 
data.

I've created a data instance at [1] which, for those like me who prefer 
graphs to angle brackets, is graphed at [2] (and generating this graph 
is evidence that it's valid RDF!).

For good measure, I put the data into Protégé - no problem there, it 
loads OK [3]. However, the (Pellet) reasoner, didn't return a result. It 
got as far as warning that it didn't understand foaf:Document (which 
isn't in my test data but is in the FOAF vocabulary) and got no further. 
I wanted to see whether it would infer at least that the properties of 
'ResourceSafeForChildren' were inherited by 'ResourceOnExampleDotOrg' - 
well, not this time. I wondered about possible reasons for this - and 
the truth is I don't know why, especially as earlier experiments with 
Protégé worked fine - but my guess is that it's tied up with the fact 
that in the earlier experiments I defined the datatype property 
wdr:includeHost within the Protégé project. I need to play with this 
some more.

After loading Protégé I did make one change to the data instance though. 
I think the 'ResourceOnExampleDotOrg' class should be defined using 
'necessary and sufficient' structures rather than just necessary. The 
data in [1] says that any instance of the class will be available from 
the example.org host. However, it doesn't say that anything on that host 
is an instance of the class which is what we actually want it to say so 
you have to add a bit of extra code to make this true - I call this 
example3a [4], graphed at [5].

Note the 'equivalent Class' property in the revised 
ResourceOnExampleDotOrg class:

   <owl:Class rdf:ID="ResourceOnExampleDotOrg">
     <owl:equivalentClass>
       <owl:Class>
         <rdfs:subClassOf>
           <owl:Restriction>
             <owl:onProperty 
rdf:resource="http://www.w3.org/2007/05/powder#includeHost" />
             <owl:hasValue>example.org</owl:hasValue>
           </owl:Restriction>
         </rdfs:subClassOf>
       </owl:Class>
     </owl:equivalentClass>
   </owl:Class>

OK, let's try and get some data out of this. I'm hoping that Andrea and 
Stasinos will be able to write some rules that can use the data but my 
approach is to use SPARQL to get the data out and then I can process it 
using Boolean logic. Using [4] as my data source...

Query 1
=======
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX wdr: <http://www.w3.org/2007/05/powder#>
SELECT DISTINCT ?x
WHERE {
   ?x rdfs:subClassOf 
<http://www.fosi.org/archive/powder/example3a.owl#ResourceSafeForChildren> .
}

This assumes I know that I'm looking for all the sub classes of a known 
class, in this case 'resourceSafeForChildren'. Unsurprisingly, it 
returns the single result: 
http://www.fosi.org/archive/powder/example3a.owl#ResourceOnExampleDotOrg 
(see [6]).

I could then parse the ResourceOnExampleDotOrg to see what it meant.

Query 2
=======
Let's assume I know a little less. I know the structure of a DR (of 
course) and I can assume that the 'Resource Set' has necessary and 
sufficient conditions and therefore we need to take into account the 
equivalent class construct.

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX wdr: <http://www.w3.org/2007/05/powder#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
SELECT DISTINCT ?x ?description ?prop ?value
WHERE {
   ?x owl:equivalentClass ?y .
   ?y rdfs:subClassOf ?restriction .
   ?restriction owl:onProperty ?prop .
   ?restriction owl:hasValue ?value .
   ?x rdfs:subClassOf ?description
}

Run against example 3a we get this:

x: http://www.fosi.org/archive/powder/example3a.owl#ResourceOnExampleDotOrg	

description: 
http://www.fosi.org/archive/powder/example3a.owl#ResourceSafeForChildren	

prop: http://www.w3.org/2007/05/powder#includeHost

value: example.org

So far so good, but this is a very simple example. What if we make like 
a little more complicated?

Example 3b [7, graphed at 8] is the same as 3a but with a slightly 
extended Resource Set thus:

<owl:Class rdf:ID="ResourceOnExampleDotOrg">
   <owl:equivalentClass>
     <owl:Class>
       <owl:intersectionOf rdf:parseType="Collection">
         <owl:Restriction>
           <owl:onProperty 
rdf:resource="http://www.w3.org/2007/05/powder#includeHost" />
           <owl:hasValue>example.org</owl:hasValue>
         </owl:Restriction>
         <owl:Restriction>
           <owl:onProperty 
rdf:resource="http://www.w3.org/2007/05/powder#pathStartsWith" />
           <owl:hasValue>foo</owl:hasValue>
         </owl:Restriction>
       </owl:intersectionOf>
     </owl:Class>
   </owl:equivalentClass>
</owl:Class>

That is, everything on example.com with a path starting with foo. Query 
2 yields no information at all since now the includeHost and 
pathStartsWith data is a level down due to the Collection. We need to 
keep what we've got on an optional query and see what else we can do.

Query 3
=======
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX wdr: <http://www.w3.org/2007/05/powder#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
SELECT DISTINCT ?x ?prop ?value ?description
WHERE {
   ?x owl:equivalentClass ?y .
   ?y owl:intersectionOf ?bn .
   ?bn rdf:first ?restriction .
   ?restriction ?prop ?value .
   ?x rdfs:subClassOf ?description
}

This is the query needed to run against a Resource Set that has a 
Collection. It yields some of the information needed - it tells us that:

1. We have a Collection that is an intersection
2. The first property/value pair is includeHost/example.org

We now need to run a second query

Query 3A
========
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX wdr: <http://www.w3.org/2007/05/powder#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
SELECT DISTINCT ?x ?prop ?value ?description
WHERE {
   ?x owl:equivalentClass ?y .
   ?y owl:intersectionOf ?bn .
   ?bn rdf:rest ?bn2
   ?bn2 rdf:first ?restriction .
   ?restriction ?prop ?value .
   ?x rdfs:subClassOf ?description
}

Notice that an extra line has been inserted (?bn rdf:rest ?bn2). We'd 
need to iterate this kind of query until we got a null result telling us 
we'd reached the end of the Collection. It's a bit of a pain but it's 
the way SPARQL works. There may be smarter way??

Processing-wise I think you'd have to start with query 3. If you got 
data, do 3A and iterate until you got no more data. If you got no data 
from query 3, do query 2.

We'll need to do more such tests but that's a start...

Phil.


[1] http://www.fosi.org/archive/powder/example3.owl
[2] http://www.w3.org/RDF/Validator/ARPServlet.tmp/servlet_5895.png
[3] http://www.fosi.org/archive/powder/example3.png
[4] http://www.fosi.org/archive/powder/example3a.owl
[5] http://www.w3.org/RDF/Validator/ARPServlet.tmp/servlet_5907.png
[6] 
http://librdf.org/query?uri=http%3A%2F%2Fwww.fosi.org%2Farchive%2Fpowder%2Fexample3a.owl&query=PREFIX+rdf%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F1999%2F02%2F22-rdf-syntax-ns%23%3E%0D%0APREFIX+rdfs%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F2000%2F01%2Frdf-schema%23%3E%0D%0APREFIX+foaf%3A+%3Chttp%3A%2F%2Fxmlns.com%2Ffoaf%2F0.1%2F%3E%0D%0APREFIX+wdr%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F2007%2F05%2Fpowder%23%3E%0D%0ASELECT+DISTINCT+%3Fx%0D%0AWHERE+%7B%0D%0A++%3Fx+rdfs%3AsubClassOf+%3Chttp%3A%2F%2Fwww.fosi.org%2Farchive%2Fpowder%2Fexample3a.owl%23ResourceSafeForChildren%3E+.%0D%0A%7D%0D%0A%0D%0A&language=sparql&Run+Query=Run+Query&.cgifields=language&.cgifields=json&.cgifields=raw
[7] http://www.fosi.org/archive/powder/example3b.owl
[8] http://www.w3.org/RDF/Validator/ARPServlet.tmp/servlet_6063.png
Received on Monday, 26 November 2007 15:45:57 GMT

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