Quaestor demo

This is a demo of the reasoning capabilities described elsewhere. To work through the demo, you need to have a Quaestor service running inside a Tomcat server: I'll take that to be running at http://localhost:8080/quaestor. You need at least Quaestor v0.3.

The Quaestor interface is documented on the front page of the Quaestor server. It uses the HTTP protocol commands to manipulate then query the server, so you need curl or some other tool which can generate HTTP GET, PUT and POST commands (the wget program can do POST, but not PUT). Or you can just talk HTTP yourself, using telnet.

1

The HTTP demo

First, create a new knowledgebase, with a PUT command. Call the knowledgebase `testing', and read a simple metadata string from stdin:

% curl --upload-file - \
    --header content-type:text/plain \
    http://localhost:8080/quaestor/kb/testing
My test knowledgebase
^D
%

Note that we have to tell Quaestor that the input is plain text. As an alternative, you can describe the new knowledgebase using RDF.

If you add the --verbose flag to the curl command line, you will see (instructive?) protocol chatter, as well as the 204 (no content) return code from the server.

Retrieving the URL http://localhost:8080/quaestor/kb, either using curl or in a web browser, will show you that you have created this knowledgebase. You can delete the knowledgebase with the HTTP DELETE operation, though you have to do this by hand, since curl doesn't support this:

% telnet localhost 8080
Trying ::1...
Connected to localhost.
Escape character is '^]'.
DELETE /quaestor/kb/testing HTTP/1.0

HTTP/1.1 204 No Content
Server: Apache-Coyote/1.1
Date: Thu, 13 Apr 2006 10:02:53 GMT
Connection: close

Connection closed by foreign host.
%

Now you can add to the knowledgebase the three sets of assertions contained in files access-control.owl, instances.n3 and identity.n3. Add these to the knowledgebase submodels ontology, people and identities respectively (the names are arbitrary, and you can use alternatives if you wish).

% curl --upload-file access-control.owl \
    http://localhost:8080/quaestor/kb/testing/ontology \
    --header content-type:application/rdf+xml
% curl --upload-file instances.n3 \
    'http://localhost:8080/quaestor/kb/testing/people?instances'
% curl --upload-file identity.n3 \
    http://localhost:8080/quaestor/kb/testing/identities
%

The two .n3 files are written in Notation 3; this is the default MIME type which Quaestor expects. The access-control.owl file, however, is written in the RDF/XML serialisation, and so we must add an appropriate Content-Type header to the upload. The instances.n3 file is uploaded with a ?instances query attached -- this tells the reasoner that these are assertions about individuals rather than types; this distinction is currently important.

If you now look again at http://localhost:8080/quaestor/kb you will see the knowledgebase and its submodels listed.

You can retrieve the individual submodels from the Quaestor service:

% curl http://localhost:8080/quaestor/kb/testing/people

will respond with the contents of the people submodel in the default Notation3 format (MIME type text/rdf+n3), and if you add --header accept:application/rdf+xml to the curl command, you'll get it in RDF/XML again. If you retrieve http://localhost:8080/quaestor/kb/testing you'll get the union of the three submodels.

There are several SPARQL queries in the demo for you to try. The query access-all.rq is:

prefix : <http://eurovotech.org/access-control.owl#>
select ?person
where { ?person a :CanSeeAllData }

You can post this file with an HTTP POST request:

% curl --header content-type:application/sparql-query \
    --data-binary @access-all.rq \
    http://localhost:8080/quaestor/kb/testing
[...]
%

This should respond with an XML document which conforms to the SPARQL response scheme. If you add --header accept:text/plain or --header accept:text/csv to the command, the reasoner will produce a response in the corresponding format. There are several other queries you can try:

access-flagged.rq

This query asks which individuals are in the flagged-data group

ask-norman.rq

This query asks the yes/no question of whether norman@astro.gla.ac.uk is allowed to see all the data.

construct-accessers.rq

This uses a SPARQL construct query to obtain a query result in RDF.

ask-badly.rq

This query is malformed (there's a missing angle bracket). The reasoner responds with an HTTP 400 status.

Finally, you can delete the knowledgebase with the HTTP DELETE command, as illustrated above.

2

The XML-RPC demo

Quaestor also has an XML-RPC interface, with an endpoint at http://localhost:8080/quaestor/xmlrpc, though it has rather less functionality at present.

The file xmlrpc-get-model.xml contains an XML-RPC method call:

<methodCall>
<methodName>get-model</methodName>
<params>
<param><value><string>testing</string></value></param>
</params>
</methodCall>

You can post this to the server as follows:

% curl --header content-type:text/xml \
    --data-binary @xmlrpc-get-model.xml \
    http://localhost:8080/quaestor/xmlrpc
%

and get a response which simply indicates that you should dereference another URL.

Slightly more useful is the query-model method, illustrated in xmlrpc-query-model.xml. This makes a SPARQL query against the model, and returns a URL which can be dereferenced to pick up the query results.

3

Links

There are SPARQL tutorials at http://www-128.ibm.com/developerworks/xml/library/j-sparql/ and http://jena.sourceforge.net/ARQ/Tutorial/.

The (rather informal) XML-RPC spec is at http://www.xmlrpc.com/spec.