| <!DOCTYPE html> |
| <html lang="en"> |
| <head> |
| |
| |
| <title>Apache Jena - Tutorial - Manipulating SPARQL using ARQ</title> |
| <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> |
| <meta name="viewport" content="width=device-width, initial-scale=1.0"> |
| |
| <link href="/css/bootstrap.min.css" rel="stylesheet" media="screen"> |
| <link href="/css/bootstrap-icons.css" rel="stylesheet" media="screen"><link rel="stylesheet" type="text/css" href="https://jena.apache.org/sass/jena.1b17c39a117e22b46db4c66f6395dc27c134a60377d87d2d5745b8600eb69722.css" integrity="sha256-GxfDmhF+IrRttMZvY5XcJ8E0pgN32H0tV0W4YA62lyI="> |
| <link rel="shortcut icon" href="/images/favicon.ico" /> |
| |
| </head> |
| |
| <body> |
| |
| <nav class="navbar navbar-expand-lg bg-body-tertiary" role="navigation"> |
| <div class="container"> |
| <div class="navbar-header"> |
| <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarNav" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation"> |
| <span class="navbar-toggler-icon"></span> |
| </button> |
| <a class="navbar-brand" href="/index.html"> |
| <img class="logo-menu" src="/images/jena-logo/jena-logo-notext-small.png" alt="jena logo">Apache Jena</a> |
| </div> |
| |
| <div class="collapse navbar-collapse" id="navbarNav"> |
| <ul class="navbar-nav me-auto mb-2 mb-lg-0"> |
| <li id="homepage" class="nav-item"><a class="nav-link" href="/index.html"><span class="bi-house"></span> Home</a></li> |
| <li id="download" class="nav-item"><a class="nav-link" href="/download/index.cgi"><span class="bi-download"></span> Download</a></li> |
| <li class="nav-item dropdown"> |
| <a href="#" class="nav-link dropdown-toggle" role="button" data-bs-toggle="dropdown" aria-expanded="false"><span class="bi-journal"></span> Learn <b class="caret"></b></a> |
| <ul class="dropdown-menu"> |
| <li class="dropdown-header">Tutorials</li> |
| <li><a class="dropdown-item" href="/tutorials/index.html">Overview</a></li> |
| <li><a class="dropdown-item" href="/documentation/fuseki2/index.html">Fuseki Triplestore</a></li> |
| <li><a class="dropdown-item" href="/documentation/notes/index.html">How-To's</a></li> |
| <li><a class="dropdown-item" href="/documentation/query/manipulating_sparql_using_arq.html">Manipulating SPARQL using ARQ</a></li> |
| <li><a class="dropdown-item" href="/tutorials/rdf_api.html">RDF core API tutorial</a></li> |
| <li><a class="dropdown-item" href="/tutorials/sparql.html">SPARQL tutorial</a></li> |
| <li><a class="dropdown-item" href="/tutorials/using_jena_with_eclipse.html">Using Jena with Eclipse</a></li> |
| <li class="dropdown-divider"></li> |
| <li class="dropdown-header">References</li> |
| <li><a class="dropdown-item" href="/documentation/index.html">Overview</a></li> |
| <li><a class="dropdown-item" href="/documentation/query/index.html">ARQ (SPARQL)</a></li> |
| <li><a class="dropdown-item" href="/documentation/io/">RDF I/O</a></li> |
| <li><a class="dropdown-item" href="/documentation/assembler/index.html">Assembler</a></li> |
| <li><a class="dropdown-item" href="/documentation/tools/index.html">Command-line tools</a></li> |
| <li><a class="dropdown-item" href="/documentation/rdfs/">Data with RDFS Inferencing</a></li> |
| <li><a class="dropdown-item" href="/documentation/geosparql/index.html">GeoSPARQL</a></li> |
| <li><a class="dropdown-item" href="/documentation/inference/index.html">Inference API</a></li> |
| <li><a class="dropdown-item" href="/documentation/ontology/">Ontology API</a></li> |
| <li><a class="dropdown-item" href="/documentation/permissions/index.html">Permissions</a></li> |
| <li><a class="dropdown-item" href="/documentation/extras/querybuilder/index.html">Query Builder</a></li> |
| <li><a class="dropdown-item" href="/documentation/rdf/index.html">RDF API</a></li> |
| <li><a class="dropdown-item" href="/documentation/rdfconnection/">RDF Connection - SPARQL API</a></li> |
| <li><a class="dropdown-item" href="/documentation/rdfstar/index.html">RDF-star</a></li> |
| <li><a class="dropdown-item" href="/documentation/shacl/index.html">SHACL</a></li> |
| <li><a class="dropdown-item" href="/documentation/shex/index.html">ShEx</a></li> |
| <li><a class="dropdown-item" href="/documentation/tdb/index.html">TDB</a></li> |
| <li><a class="dropdown-item" href="/documentation/tdb2/index.html">TDB2</a></li> |
| <li><a class="dropdown-item" href="/documentation/query/text-query.html">Text Search</a></li> |
| </ul> |
| </li> |
| |
| <li class="nav-item dropdown"> |
| <a href="#" class="nav-link dropdown-toggle" role="button" data-bs-toggle="dropdown" aria-expanded="false"><span class="bi-journal-code"></span> Javadoc <b class="caret"></b></a> |
| <ul class="dropdown-menu"> |
| <li><a class="dropdown-item" href="/documentation/javadoc.html">All Javadoc</a></li> |
| <li><a class="dropdown-item" href="/documentation/javadoc/arq/">ARQ</a></li> |
| <li><a class="dropdown-item" href="/documentation/javadoc/fuseki2/">Fuseki</a></li> |
| <li><a class="dropdown-item" href="/documentation/javadoc/geosparql/">GeoSPARQL</a></li> |
| <li><a class="dropdown-item" href="/documentation/javadoc/jena/">Jena Core</a></li> |
| <li><a class="dropdown-item" href="/documentation/javadoc/permissions/">Permissions</a></li> |
| <li><a class="dropdown-item" href="/documentation/javadoc/extras/querybuilder/">Query Builder</a></li> |
| <li><a class="dropdown-item" href="/documentation/javadoc/shacl/">SHACL</a></li> |
| <li><a class="dropdown-item" href="/documentation/javadoc/tdb/">TDB</a></li> |
| <li><a class="dropdown-item" href="/documentation/javadoc/text/">Text Search</a></li> |
| </ul> |
| </li> |
| </ul> |
| <form class="d-flex" role="search" action="/search" method="GET"> |
| <div class="input-group"> |
| <input class="form-control border-end-0 border m-0" type="search" name="q" id="search-query" placeholder="Search...." aria-label="Search" style="width: 10rem;"> |
| <button class="btn btn-outline-secondary border-start-0 border" type="submit"> |
| <i class="bi-search"></i> |
| </button> |
| </div> |
| </form> |
| <ul class="navbar-nav"> |
| <li id="ask" class="nav-item"><a class="nav-link" href="/help_and_support/index.html" title="Ask"><span class="bi-patch-question"></span><span class="text-body d-none d-xxl-inline"> Ask</span></a></li> |
| |
| <li class="nav-item dropdown"> |
| <a href="#" title="Get involved" class="nav-link dropdown-toggle" role="button" data-bs-toggle="dropdown" aria-expanded="false"><span class="bi-megaphone"></span><span class="text-body d-none d-xxl-inline"> Get involved </span><b class="caret"></b></a> |
| <ul class="dropdown-menu"> |
| <li><a class="dropdown-item" href="/getting_involved/index.html">Contribute</a></li> |
| <li><a class="dropdown-item" href="/help_and_support/bugs_and_suggestions.html">Report a bug</a></li> |
| <li class="dropdown-divider"></li> |
| <li class="dropdown-header">Project</li> |
| <li><a class="dropdown-item" href="/about_jena/about.html">About Jena</a></li> |
| <li><a class="dropdown-item" href="/about_jena/architecture.html">Architecture</a></li> |
| <li><a class="dropdown-item" href="/about_jena/citing.html">Citing</a></li> |
| <li><a class="dropdown-item" href="/about_jena/team.html">Project team</a></li> |
| <li><a class="dropdown-item" href="/about_jena/contributions.html">Related projects</a></li> |
| <li><a class="dropdown-item" href="/about_jena/roadmap.html">Roadmap</a></li> |
| <li><a class="dropdown-item" href="/about_jena/security-advisories.html">Security Advisories</a></li> |
| <li class="dropdown-divider"></li> |
| <li class="dropdown-header">ASF</li> |
| <li><a class="dropdown-item" href="https://www.apache.org/">Apache Software Foundation</a></li> |
| <li><a class="dropdown-item" href="https://www.apache.org/foundation/sponsorship.html">Become a Sponsor</a></li> |
| <li><a class="dropdown-item" href="https://www.apache.org/licenses/LICENSE-2.0">License</a></li> |
| <li><a class="dropdown-item" href="https://www.apache.org/security/">Security</a></li> |
| <li><a class="dropdown-item" href="https://www.apache.org/foundation/thanks.html">Thanks</a></li> |
| </ul> |
| </li> |
| |
| |
| |
| |
| <li class="nav-item" id="edit"><a class="nav-link" href="https://github.com/apache/jena-site/edit/main/source/documentation/query/manipulating_sparql_using_arq.md" title="Edit this page on GitHub"><span class="bi-pencil-square"></span><span class="text-body d-none d-xxl-inline"> Edit this page</span></a></li> |
| </ul> |
| </div> |
| </div> |
| </nav> |
| |
| <div class="container"> |
| <div class="row"> |
| <div class="col-md-12"> |
| |
| <div id="breadcrumbs"> |
|
|
|
|
|
|
|
|
|
|
|
|
| <ol class="breadcrumb mt-4 p-2 bg-body-tertiary">
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| <li class="breadcrumb-item"><a href='/documentation'>DOCUMENTATION</a></li>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| <li class="breadcrumb-item"><a href='/documentation/query'>QUERY</a></li>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| <li class="breadcrumb-item active">MANIPULATING SPARQL USING ARQ</li>
|
|
|
|
|
|
|
|
|
| </ol>
|
|
|
|
|
|
|
| |
| </div> |
| <h1 class="title">Tutorial - Manipulating SPARQL using ARQ</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="#inserting-values-simple-prepared-statements">Inserting values (simple prepared statements)</a></li> |
| <li><a href="#making-a-query-from-scratch">Making a Query from Scratch</a></li> |
| <li><a href="#navigating-and-tinkering-visitors">Navigating and Tinkering: Visitors</a></li> |
| <li><a href="#transforming-the-algebra">Transforming the Algebra</a></li> |
| </ul> |
| </nav> |
| </aside> |
| <article class="flex-column me-lg-4"> |
| <p>When you’ve been working with SPARQL you quickly find that static |
| queries are restrictive. Maybe you want to vary a value, perhaps add a |
| filter, alter the limit, etc etc. Being an impatient sort you dive in to |
| the query string, and it works. But what about <a href="http://xkcd.com/327/">little Bobby |
| Tables</a>? And, even if you |
| sanitise your inputs, string manipulation is a fraught process and |
| syntax errors await you. Although it might seem harder than string |
| munging, the ARQ API is your friend in the long run.</p> |
| <p><em>Originally published on the <a href="https://web.archive.org/web/20151107135044/http://researchrevealed.ilrt.bris.ac.uk/?p=35">Research Revealed project |
| blog</a></em></p> |
| <h2 id="inserting-values-simple-prepared-statements">Inserting values (simple prepared statements)</h2> |
| <p>Let’s begin with something simple. Suppose we wanted to restrict the |
| following query to a particular person:</p> |
| <pre><code> select * { ?person <http://xmlns.com/foaf/0.1/name> ?name } |
| </code></pre> |
| <p><code>String#replaceAll</code> would work, but there is a safer way. |
| <code>QueryExecutionFactory</code> in most cases lets you supply a <code>QuerySolution</code> |
| with which you can prebind values.</p> |
| <pre><code> QuerySolutionMap initialBinding = new QuerySolutionMap(); |
| initialBinding.add("name", personResource); |
| qe = QueryExecutionFactory.create(query, dataset, initialBinding); |
| </code></pre> |
| <p>This is often much simpler than the string equivalent since you don’t |
| have to escape quotes in literals. (Beware that this doesn’t work for |
| <code>sparqlService</code>, which is a great shame. It would be nice to spend some |
| time remedying that.)</p> |
| <h2 id="making-a-query-from-scratch">Making a Query from Scratch</h2> |
| <p>The previously mentioned limitation is due to the fact that prebinding |
| doesn’t actually change the query at all, but the execution of that |
| query. So what how do we really alter queries?</p> |
| <p>ARQ provides two ways to work with queries: at the syntax level (<code>Query</code> |
| and <code>Element</code>), or the algebra level (<code>Op</code>). The distinction is clear in |
| filters:</p> |
| <pre><code> SELECT ?s { ?s <http://example.com/val> ?val . FILTER ( ?val < 20 ) } |
| </code></pre> |
| <p>If you work at the syntax level you’ll find that this looks (in pseudo |
| code) like:</p> |
| <pre><code> (GROUP (PATTERN ( ?s <http://example.com/val> ?val )) (FILTER ( < ?val 20 ) )) |
| </code></pre> |
| <p>That is there’s a group containing a triple pattern and a filter, just |
| as you see in the query. The algebra is different, and we can see it |
| using <code>arq.qparse --print op</code></p> |
| <pre><code> $ java arq.qparse --print op 'SELECT ?s { ?s <http://example.com/val> ?val . FILTER ( ?val < 20 ) }' |
| (base <file:///...> |
| (project (?s) |
| (filter (< ?val 20) |
| (bgp (triple ?s <http://example.com/val> ?val))))) |
| </code></pre> |
| <p>Here the filter contains the pattern, rather than sitting next to it. |
| This form makes it clear that the expression is filtering the pattern.</p> |
| <p>Let’s create that query from scratch using ARQ. We begin with some |
| common pieces: the triple to match, and the expression for the filter.</p> |
| <pre><code> // ?s ?p ?o . |
| Triple pattern = |
| Triple.create(Var.alloc("s"), Var.alloc("p"), Var.alloc("o")); |
| // ( ?s < 20 ) |
| Expr e = new E_LessThan(new ExprVar("s"), new NodeValueInteger(20)); |
| </code></pre> |
| <p><code>Triple</code> should be familiar from jena. <code>Var</code> is an extension of <code>Node</code> |
| for variables. <code>Expr</code> is the root interface for expressions, those |
| things that appear in <code>FILTER</code> and <code>LET</code>.</p> |
| <p>First the syntax route:</p> |
| <pre><code> ElementTriplesBlock block = new ElementTriplesBlock(); // Make a BGP |
| block.addTriple(pattern); // Add our pattern match |
| ElementFilter filter = new ElementFilter(e); // Make a filter matching the expression |
| ElementGroup body = new ElementGroup(); // Group our pattern match and filter |
| body.addElement(block); |
| body.addElement(filter); |
| |
| Query q = QueryFactory.make(); |
| q.setQueryPattern(body); // Set the body of the query to our group |
| q.setQuerySelectType(); // Make it a select query |
| q.addResultVar("s"); // Select ?s |
| </code></pre> |
| <p>Now the algebra:</p> |
| <pre><code> Op op; |
| BasicPattern pat = new BasicPattern(); // Make a pattern |
| pat.add(pattern); // Add our pattern match |
| op = new OpBGP(pat); // Make a BGP from this pattern |
| op = OpFilter.filter(e, op); // Filter that pattern with our expression |
| op = new OpProject(op, Arrays.asList(Var.alloc("s"))); // Reduce to just ?s |
| Query q = OpAsQuery.asQuery(op); // Convert to a query |
| q.setQuerySelectType(); // Make is a select query |
| </code></pre> |
| <p>Notice that the query form (<code>SELECT, CONSTRUCT, DESCRIBE, ASK</code>) isn’t |
| part of the algebra, and we have to set this in the query (although |
| SELECT is the default). <code>FROM</code> and <code>FROM NAMED</code> are similarly absent.</p> |
| <h2 id="navigating-and-tinkering-visitors">Navigating and Tinkering: Visitors</h2> |
| <p>You can also look around the algebra and syntax using visitors. Start by |
| extending <code>OpVisitorBase</code> (<code>ElementVisitorBase</code>) which stubs out the |
| interface so you can concentrate on the parts of interest, then walk |
| using <code>OpWalker.walk(Op, OpVisitor)</code> |
| (<code>ElementWalker.walk(Element, ElementVisitor)</code>). These work bottom up.</p> |
| <p>For some alterations, like manipulating triple matches in place, |
| visitors will do the trick. They provide a simple way to get to the |
| right parts of the query, and you can alter the pattern backing BGPs in |
| both the algebra and syntax. Mutation isn’t consistently available, |
| however, so don’t depend on it.</p> |
| <h2 id="transforming-the-algebra">Transforming the Algebra</h2> |
| <p>So far there is no obvious advantage in using the algebra. The real |
| power is visible in transformers, which allow you to reorganise an |
| algebra completely. ARQ makes extensive use of transformations to |
| simplify and optimise query execution.</p> |
| <p>In Research Revealed I wrote some code to take a number of constraints |
| and produce a query. There were a number of ways to do this, but one way |
| I found was to generate ops from each constraint and join the results:</p> |
| <pre><code> for (Constraint con: cons) { |
| op = OpJoin.create(op, consToOp(cons)); // join |
| } |
| </code></pre> |
| <p>The result was a perfectly correct mess, which is only barely readable |
| with just three conditions:</p> |
| <pre><code> (join |
| (join |
| (filter (< ?o0 20) (bgp (triple ?s <urn:ex:prop0> ?o0))) |
| (filter (< ?o1 20) (bgp (triple ?s <urn:ex:prop1> ?o1)))) |
| (filter (< ?o2 20) (bgp (triple ?s <urn:ex:prop2> ?o2)))) |
| </code></pre> |
| <p>Each of the constraints is a filter on a bgp. This can be made much more |
| readable by moving the filters out, and merging the triple patterns. We |
| can do this with the following <code>Transform</code>:</p> |
| <pre><code> class QueryCleaner extends TransformBase |
| { |
| @Override |
| public Op transform(OpJoin join, Op left, Op right) { |
| // Bail if not of the right form |
| if (!(left instanceof OpFilter && right instanceof OpFilter)) return join; |
| OpFilter leftF = (OpFilter) left; |
| OpFilter rightF = (OpFilter) right; |
| |
| // Add all of the triple matches to the LHS BGP |
| ((OpBGP) leftF.getSubOp()).getPattern().addAll(((OpBGP) rightF.getSubOp()).getPattern()); |
| // Add the RHS filter to the LHS |
| leftF.getExprs().addAll(rightF.getExprs()); |
| return leftF; |
| } |
| } |
| ... |
| op = Transformer.transform(new QueryCleaner(), op); // clean query |
| </code></pre> |
| <p>This looks for joins of the form:</p> |
| <pre><code> (join |
| (filter (exp1) (bgp1)) |
| (filter (exp2) (bgp2))) |
| </code></pre> |
| <p>And replaces it with:</p> |
| <pre><code> (filter (exp1 && exp2) (bgp1 && bgp2)) |
| </code></pre> |
| <p>As we go through the original query all joins are removed, and the |
| result is:</p> |
| <pre><code> (filter (exprlist (< ?o0 20) (< ?o1 20) (< ?o2 20)) |
| (bgp |
| (triple ?s <urn:ex:prop0> ?o0) |
| (triple ?s <urn:ex:prop1> ?o1) |
| (triple ?s <urn:ex:prop2> ?o2) |
| )) |
| </code></pre> |
| <p>That completes this brief introduction. There is much more to ARQ, of |
| course, but hopefully you now have a taste for what it can do.</p> |
| |
| </article> |
| |
| <aside class="text-muted align-self-start mb-3 mb-xl-5 p-0 d-none d-xl-flex flex-column sticky-top"> |
| <h2 class="h6 sticky-top m-0 p-2 bg-body-tertiary">On this page</h2> |
| <nav id="TableOfContents"> |
| <ul> |
| <li><a href="#inserting-values-simple-prepared-statements">Inserting values (simple prepared statements)</a></li> |
| <li><a href="#making-a-query-from-scratch">Making a Query from Scratch</a></li> |
| <li><a href="#navigating-and-tinkering-visitors">Navigating and Tinkering: Visitors</a></li> |
| <li><a href="#transforming-the-algebra">Transforming the Algebra</a></li> |
| </ul> |
| </nav> |
| </aside> |
| </main> |
| |
| </div> |
| </div> |
| </div> |
| |
| <footer class="bd-footer py-4 py-md-5 mt-4 mt-lg-5 bg-body-tertiary"> |
| <div class="container" style="font-size:80%" > |
| <p> |
| Copyright © 2011–2024 The Apache Software Foundation, Licensed under the |
| <a href="https://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>. |
| </p> |
| <p> |
| Apache Jena, Jena, the Apache Jena project logo, Apache and the Apache feather logos are trademarks of |
| The Apache Software Foundation. |
| <br/> |
| <a href="https://privacy.apache.org/policies/privacy-policy-public.html" |
| >Apache Software Foundation Privacy Policy</a>. |
| </p> |
| </div> |
| </footer> |
| |
| <script src="/js/popper.min.js.js" type="text/javascript"></script> |
| <script src="/js/bootstrap.min.js" type="text/javascript"></script> |
| <script src="/js/improve.js" type="text/javascript"></script> |
| |
| <script type="text/javascript"> |
| (function() { |
| 'use strict' |
| |
| |
| |
| const links = document.querySelectorAll(`a[href="${window.location.pathname}"]`) |
| if (links !== undefined && links !== null) { |
| for (const link of links) { |
| |
| link.classList.add('active') |
| let parentElement = link.parentElement |
| let count = 0 |
| const levelsLimit = 4 |
| |
| |
| |
| |
| |
| while (['UL', 'LI'].includes(parentElement.tagName) && count <= levelsLimit) { |
| if (parentElement.tagName === 'LI') { |
| |
| |
| |
| parentElement.querySelector('a:first-child').classList.add('active') |
| } |
| parentElement = parentElement.parentElement |
| count++ |
| } |
| } |
| } |
| })() |
| </script> |
| |
| </body> |
| </html> |
