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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><b>Note:</b> This service is not currently available. This page is
retained for historical interest.</p>

<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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author	Chris Cannam
date	Wed, 08 Nov 2017 15:27:23 +0000
parents	d95267afa12a
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