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       <title>Henry - a DSP-driving SPARQL end-point</title>
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       <a href="http://dbtune.org/"><h1 style="font-size: 250%;">DBTune.org</h1></a>
       <div id="tagline">Henry - a DSP-driving SPARQL end-point<!-- - yves _at_ dbtune _dot_ org--></div>
       <h2><a name="intro" id="intro"></a>1. Introduction</h2>
       <p>
       This server hosts a <a href="http://www.w3.org/TR/rdf-sparql-query/">SPARQL</a>
       end-point able to perform audio processing tasks to answer a particular query.
       It builds on top of <a href="http://www.w3.org/TeamSubmission/n3/">N3</a> and <a href="http://www.cs.sunysb.edu/~kifer/dood/tr-tutorial.html">
       Transaction Logic</a>. More details to come.
       </p>
       <p>
       Henry therefore implements a Music-related <a href="http://www-personal.si.umich.edu/~rfrost/courses/SI110/readings/In_Out_and_Beyond/Semantic_Web.pdf">Semantic Web agent</a>:
       an agent processing machine-readable web content and audio content
       to publish new data.
       </p>
       <h2><a name="details" id="details"></a>2. Details</h2>
       <p>
       <a href="http://blog.dbtune.org/post/2007/12/12/HENRY%3A-A-small-N3-parser/reasoner-for-SWI-Prolog">Henry</a> was initally intended to be a small application
       on top of a <a href="http://www.swi-prolog.org/">SWI-Prolog</a> <a href="http://code.google.com/p/km-rdf/source/browse/trunk/n3/n3_dcg.pl">N3 parser</a>,
       interpreting parsed N3 rules as entailment rules within the <a href="http://e-culture.multimedian.nl/software/ClioPatria.shtml">SWI-Prolog
       Semantic Web server</a>.
       </p>
       <p>
       Now, Henry provides the ability to easily register new audio processing builtin predicates (which may be discovered at querying time).
       Henry works on top of a quad-store <i>m</i> and a binary store <i>b</i>.
       </p>
       <p>
       A simplistic version of the
       behavior of Henry is the following.
       When processing a SPARQL query <i>q</i>, Henry gets through the following steps:
       <ol>
       <li> For every newly appearing web identifier <i>i</i> in <i>q</i>, dereference it, and then:</li>
       <ul>
       <li>If the representation is RDF, store it in <i>m</i>. If <i>i</i> is a property and its representation
       links to a built-in implementation matching the current platform, get it ;</li>
       <li>If the representation is N3, store it in <i>m</i> and register the corresponding rules ;</li>
       <li>If the representation is of a known mime-type, cache it in <i>b</i> ;</li>
       </ul>
       <li> For every triple pattern <i>p</i> in <i>q</i>, the possible solutions are:</li>
       <ul>
       <li>Instantiations of <i>p</i> in <i>m</i> ;</li>
       <li>If <i>p</i> is in the head of a rule, solutions of step <i>2</i> with the body of the rule as <i>q</i> (plus a few extra things to deal
       with equivalency, lists, existentials in the head, etc.) ;</li>
       <li>If <i>p=(s_p,p_p,o_p)</i> where <i>p_p</i> is a built-in predicate, solutions derived using this built-in (update the state of <i>b</i> accordingly)</li>
       </ul>
       </ol>
       </p>
       <p>
       This implementation is still in the early stages, and still a bit experimental, it may perfectly die horribly :-) A look at
       the <a href="http://code.google.com/p/km-rdf/issues/list">issue tracker</a> may give insights on what is still buggy.
       Also, the server running this service is quite.... slow :)
       </p>
       <h2><a name="use" id="use"></a>3. Using this service</h2>
       <p>
       There is a raw SPARQL end point at <pre>http://dbtune.org/henry/sparql/</pre>.
       </p>
       <p>
       A <a href="http://dbtune.org/henry/store/">web interface</a> is also available. Get in the <b>Query database</b> page, make sure you choose <b>SPARQL</b>
       as your query language, and check that the entailment is set to <b>n3</b> (it should be the default, anyway).
       </p>
       <p>
       A query involving only builtins (no N3 rules) is the following. It computes MFCC models for two tracks and compute
       their Kullback-Leiber divergence:
       </p>
       <pre>
       select ?d
       where
+      {
       &lt;http://dbtune.org/audio/Den-Nostalia.ogg&gt; &lt;http://purl.org/ontology/dsp/cache&gt; ?local.
       ?local &lt;http://purl.org/ontology/dsp/aspl_decode&gt; ?sig.
       ?sig &lt;http://purl.org/ontology/vamp/qm-mfccparameters&gt; (?means1 ?vars1).
       &lt;http://dbtune.org/audio/Both-Axel.ogg&gt; &lt;http://purl.org/ontology/dsp/cache&gt; ?local2 .
       ?local2 &lt;http://purl.org/ontology/dsp/aspl_decode&gt; ?sig2.
       ?sig2 &lt;http://purl.org/ontology/vamp/qm-mfccparameters&gt; (?means2 ?vars2).
       ((?means1 ?vars1) (?means2 ?vars2)) &lt;http://purl.org/ontology/dsp/mfcc_kldiv&gt; ?d
+      }
       </pre>
       <p>
       This is a pretty huge query!
       But, using a simple <a href="http://code.google.com/p/km-rdf/source/browse/trunk/henry/dsp-n3/similarity.n3">N3 rule</a>, we can reduce that to the following query:
       </p>
       <pre>
       PREFIX sim: &lt;http://purl.org/ontology/similarity/&gt;
       SELECT ?sim
       WHERE
+      {
       (&lt;http://dbtune.org/audio/Den-Nostalia.ogg&gt; &lt;http://dbtune.org/audio/Both-Axel.ogg&gt;) sim:div ?sim
+      }
       </pre>
       <p>
       Another example is the following, computing key change events as specified by the <a href="http://purl.org/ontology/af/">Audio Features
       ontology</a>.
       using the <a href="http://www.elec.qmul.ac.uk/digitalmusic/downloads/index.html#qm-vamp-plugins">key
       detection Vamp plugin in the Queen Mary plugin set</a> and <a href="http://code.google.com/p/km-rdf/source/browse/trunk/henry/dsp-n3/vamp.n3">this N3
       rule</a>:
       </p>
       <pre>
       select ?start ?key where {
       &lt;http://dbtune.org/audio/Both-Axel.ogg&gt; mo:encodes ?sig.
       ?sig mo:time ?time.
       ?time tl:timeline ?tl.
       _:evt a af:KeyChange;
               event:time [tl:at ?start; tl:timeline ?tl] ;
               af:new_key ?key }
       </pre>
       <h2><a name="code" id="code"></a>4. Code</h2>
       <p>
       All the code is open source and available in our <a href="http://code.google.com/p/km-rdf">Google code project</a>.
       </p>
       <!--<h2><a name="missing" id="missing"></a>5. Things missing</h2>
       <p>Linked data access!! We are implementing the mechanism we use in <a href="http://sonictruths.net/dm.html#SBSimilarity">SBSimilarity</a>.</p>
       -->
       <!--<h2><a name="ack" id="ack"></a>5. Acknowledgements</h2>
       <p>
       Thanks to David Pastor who wrote the <a href="http://www.vamp-plugins.org/">Vamp</a> to <a href="http://www.swi-prolog.org/">SWI-Prolog</a>
       interface!
       </p>-->
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