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| <h1 class="title">ARQ - JavaScript SPARQL Functions</h1> |
| |
| |
| <main class="d-flex flex-xl-row flex-column"> |
| |
| <aside class="text-muted align-self-start mb-3 p-0 d-xl-none d-block"> |
| <h2 class="h6 sticky-top m-0 p-2 bg-body-tertiary">On this page</h2> |
| <nav id="TableOfContents"> |
| <ul> |
| <li><a href="#requirements">Requirements</a></li> |
| <li><a href="#enabling-and-loading-javascript-functions">Enabling and Loading JavaScript functions</a></li> |
| <li><a href="#identifying-callable-functions">Identifying callable functions</a></li> |
| <li><a href="#using-javascript-functions">Using JavaScript functions</a> |
| <ul> |
| <li><a href="#arguments-and-function-results">Arguments and Function Results</a></li> |
| </ul> |
| </li> |
| <li><a href="#example">Example</a></li> |
| <li><a href="#use-with-fuseki">Use with Fuseki</a></li> |
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| <article class="flex-column me-lg-4"> |
| <p>ARQ supports writing |
| <a href="https://www.w3.org/TR/sparql11-query/#extensionFunctions">custom SPARQL functions</a> |
| in JavaScript. These functions can be used in FILTERs and for calculating |
| values to assign with AS in BIND and SELECT expressions.</p> |
| <p>XSD datatypes for strings, numbers and booleans are converted to the |
| native JavaScript datatypes. RDFterms that do not fit easily into |
| JavaScript datatypes are handled with a object class <code>NV</code>.</p> |
| <p>Applications should be aware that there are risks in exposing a script engine |
| with full computational capabilities through SPARQL. Script functions are only |
| as secure as the script engine environment they run in.</p> |
| <h2 id="requirements">Requirements</h2> |
| <p>ARQ requires a javascript engine such as <a href="https://www.graalvm.org/">GraalVM</a> to |
| be added to the classpath.</p> |
| <pre tabindex="0"><code> <properties> |
| <ver.graalvm>....</ver.graalvm> |
| ... |
| </code></pre><pre tabindex="0"><code> <dependency> |
| <groupId>org.graalvm.js</groupId> |
| <artifactId>js</artifactId> |
| <version>${ver.graalvm}</version> |
| </dependency> |
| |
| <dependency> |
| <groupId>org.graalvm.js</groupId> |
| <artifactId>js-scriptengine</artifactId> |
| <version>${ver.graalvm}</version> |
| </dependency> |
| </code></pre><h2 id="enabling-and-loading-javascript-functions">Enabling and Loading JavaScript functions</h2> |
| <p>JavaScript is loaded from an external file using the context setting |
| “<a href="http://jena.apache.org/ARQ#js-library%22">http://jena.apache.org/ARQ#js-library"</a>. This can be written as |
| <code>arq:js-library</code> for commands and Fuseki configuration files.</p> |
| <p>Access to the script engine must be enabled at runtime. |
| The Java system property to do this is <code>jena:scripting</code>.</p> |
| <p>Example:</p> |
| <pre><code>export JVM_ARGS=-Djena:scripting=true |
| sparql --set arq:js-library=SomeFile.js --data ... --query ... |
| </code></pre> |
| <p>and for MS Windows:</p> |
| <pre><code>set JVM_ARGS=-Djena:scripting=true |
| sparql --set arq:js-library=SomeFile.js --data ... --query ... |
| </code></pre> |
| <p>will execute on the data with the JavaScript functions from file |
| “SomeFile.js” available.</p> |
| <p>JavaScript functions can also be set from a string directly from within Java using constant |
| <code>ARQ.symJavaScriptFunctions</code> (“<a href="http://jena.apache.org/ARQ#js-functions%22)">http://jena.apache.org/ARQ#js-functions")</a>.</p> |
| <p><strong>WARNING:</strong> Enabling this feature exposes the majority of the underlying scripting engine directly to SPARQL queries so |
| may provide a vector for arbitrary code execution. Therefore it is recommended that this feature remain disabled for |
| any publicly accessible deployment that utilises the ARQ query engine.</p> |
| <h2 id="identifying-callable-functions">Identifying callable functions</h2> |
| <p>The context setting ““<a href="http://jena.apache.org/ARQ#scriptAllowList%22">http://jena.apache.org/ARQ#scriptAllowList"</a> is used to |
| provide a comma-separated list of function names, which are the local part of |
| the URI, that are allowed to be called |
| as custom script functions.</p> |
| <p>This can be written as <code>arq:scriptAllowList</code> for commands and Fuseki configuration files. |
| It is the java constant <code>ARQ.symCustomFunctionScriptAllowList</code></p> |
| <pre><code>sparql --set arq:js-library=SomeFile.js \ |
| --set arq:scriptAllowList=toCamelCase,anotherFunction |
| --data ... --query ... |
| </code></pre> |
| <p>and a query of:</p> |
| <pre><code>PREFIX js: <http://jena.apache.org/ARQ/jsFunction#> |
| |
| SELECT ?input (js:toCamelCase(?input) AS ?X) |
| { |
| VALUES ?input { "some woRDs to PROCESS" } |
| } |
| </code></pre> |
| <h2 id="using-javascript-functions">Using JavaScript functions</h2> |
| <p>SPARQL functions implemented in JavaScript are automatically called when a |
| URI starting “<a href="http://jena.apache.org/ARQ/jsFunction#%22">http://jena.apache.org/ARQ/jsFunction#"</a> used.</p> |
| <p>This can conveniently be abbreviated by:</p> |
| <pre><code>PREFIX js: <http://jena.apache.org/ARQ/jsFunction#> |
| </code></pre> |
| <h3 id="arguments-and-function-results">Arguments and Function Results</h3> |
| <p><code>xsd:string</code> (a string with no language tag), any XSD numbers (integer, |
| decimal, float, double and all the derived types) and <code>xsd:boolean</code> are |
| converted to JavaScript string, number and boolean respectively.</p> |
| <p>SPARQL functions must return a value. When a function returns a value, |
| it can be one of these JavaScript native datatypes, in which case the |
| reverse conversion is applied back to XSD datatypes. For numbers, the |
| conversion is back to <code>xsd:integer</code> (if it has no fractional part) or |
| <code>xsd:double</code>.</p> |
| <p>The JavaScript function can also create <code>NodeValue</code> (or <code>NV</code>) objects |
| for other datatypes by calling Java from within the JavaScript script |
| engine of the Java runtime.</p> |
| <p>URIs are passed as <code>NV</code> object and are available in JavaScript as a string.</p> |
| <p>The class <code>NV</code> is used for all other RDF terms.</p> |
| <p>Returning JavaScript <code>null</code> is the error indicator and a SPARQL |
| expression error (<code>ExprEvalException</code>) is raised, like any other |
| expression error in SPARQL. That, in turn, will cause the whole |
| expression the function is part of to evaluate to an error (unless |
| a special form like <code>COALESCE</code> is used). In a <code>FILTER</code> that typically |
| makes the filter evaluate to “false”.</p> |
| <h2 id="example">Example</h2> |
| <p>Suppose “functions.js” contains code to camel case words in a string. |
| For example, “some words to process " becomes “someWordsToProcess”.</p> |
| <pre><code>// CamelCase a string |
| // Words to be combined are separated by a space in the string. |
| |
| function toCamelCase(str) { |
| return str |
| .split(' ') |
| .map(cc) |
| .join(''); |
| } |
| |
| function ucFirst(word) { |
| return word.charAt(0).toUpperCase() + word.slice(1).toLowerCase(); |
| } |
| |
| function lcFirst(word) { |
| return word.toLowerCase(); |
| } |
| |
| function cc(word,index) { |
| return (index == 0) ? lcFirst(word) : ucFirst(word); |
| } |
| </code></pre> |
| <p>and the query <code>Q.rq</code></p> |
| <pre><code>PREFIX js: <http://jena.apache.org/ARQ/jsFunction#> |
| |
| SELECT ?input (js:toCamelCase(?input) AS ?X) |
| { |
| VALUES ?input { "some woRDs to PROCESS" } |
| } |
| </code></pre> |
| <p>which results in:</p> |
| <pre><code>-------------------------------------------------- |
| | input | X | |
| ================================================== |
| | "some woRDs to PROCESS" | "someWordsToProcess" | |
| -------------------------------------------------- |
| </code></pre> |
| <h2 id="use-with-fuseki">Use with Fuseki</h2> |
| <p>The context setting can be provided on the command line starting the |
| server, for example:</p> |
| <pre><code>export JVM_ARGS=-Djena:scripting=true |
| fuseki --set arq:js-library=functions.js \ |
| --set arq:scriptAllowList=toCamelCase \ |
| --mem /ds |
| </code></pre> |
| <p>or it can be specified in the server configuration file <code>config.ttl</code>:</p> |
| <pre><code>PREFIX : <#> |
| PREFIX fuseki: <http://jena.apache.org/fuseki#> |
| PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> |
| PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> |
| PREFIX ja: <http://jena.hpl.hp.com/2005/11/Assembler#> |
| |
| [] rdf:type fuseki:Server ; |
| # Set the server-wide context |
| ja:context [ |
| ja:cxtName "arq:js-library" ; |
| ja:cxtValue "/filepath/functions.js" |
| ] ; |
| ja:context [ |
| ja:cxtName "arq:scriptAllowList" ; |
| ja:cxtValue "toCamelCase" |
| ] ; |
| . |
| |
| <#service> rdf:type fuseki:Service; |
| rdfs:label "Dataset"; |
| fuseki:name "ds"; |
| fuseki:serviceQuery "sparql"; |
| fuseki:dataset <#dataset> ; |
| . |
| |
| <#dataset> rdf:type ja:DatasetTxnMem; |
| ja:data <file:D.trig>; |
| . |
| </code></pre> |
| <p>and used as:</p> |
| <pre><code>export JVM_ARGS=-Djena:scripting=true |
| fuseki --conf config.ttl |
| </code></pre> |
| |
| </article> |
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| <nav id="TableOfContents"> |
| <ul> |
| <li><a href="#requirements">Requirements</a></li> |
| <li><a href="#enabling-and-loading-javascript-functions">Enabling and Loading JavaScript functions</a></li> |
| <li><a href="#identifying-callable-functions">Identifying callable functions</a></li> |
| <li><a href="#using-javascript-functions">Using JavaScript functions</a> |
| <ul> |
| <li><a href="#arguments-and-function-results">Arguments and Function Results</a></li> |
| </ul> |
| </li> |
| <li><a href="#example">Example</a></li> |
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