| <!DOCTYPE html> |
| <html lang="en"> |
| <head> |
| |
| |
| <title>Apache Jena - ARQ - Lateral Join</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/lateral-join.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">LATERAL JOIN</li>
|
|
|
|
|
|
|
|
|
| </ol>
|
|
|
|
|
|
|
| |
| </div> |
| <h1 class="title">ARQ - Lateral Join</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> |
| <ul> |
| <li> |
| <ul> |
| <li><a href="#syntax">Syntax</a></li> |
| <li><a href="#evaluation">Evaluation</a></li> |
| <li><a href="#variable-assignment">Variable assignment</a></li> |
| <li><a href="#variable-scopes">Variable Scopes</a></li> |
| </ul> |
| </li> |
| <li><a href="#notes">Notes</a></li> |
| </ul> |
| </li> |
| <li><a href="#sparql-specification-additional-material">SPARQL Specification Additional Material</a> |
| <ul> |
| <li><a href="#syntax-1">Syntax</a></li> |
| <li><a href="#algebra">Algebra</a></li> |
| <li><a href="#evaluation-1">Evaluation</a></li> |
| </ul> |
| </li> |
| </ul> |
| </nav> |
| </aside> |
| <article class="flex-column me-lg-4"> |
| <p>Lateral joins using the keyword <code>LATERAL</code> were introduced in Apache Jena 4.7.0.</p> |
| <p>A <code>LATERAL</code> join is like a foreach loop, looping on the results from the |
| left-hand side (LHS), the pattern before the <code>LATERAL</code> keyword, and executing |
| the right-hand side (RHS) query pattern once for each row, with the variables |
| from the input LHS in-scope during each RHS evaluation.</p> |
| <p>A regular join only executes the RHS once, and the variables from the LHS are |
| used for the join condition after evaluation of the left and right |
| sub-patterns.</p> |
| <p>Another way to think of a lateral join is as a <code>flatmap</code>.</p> |
| <p>Examples:</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#080;font-style:italic">## Get exactly one label for each subject with type `:T`</span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#666">*</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#b8860b">?s</span> <span style="color:#00f;font-weight:bold">rdf</span>:<span style="color:#008000;font-weight:bold">type</span> :<span style="color:#008000;font-weight:bold">T</span> |
| </span></span><span style="display:flex;"><span> <span style="">LATERAL</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#666">*</span> { <span style="color:#b8860b">?s</span> <span style="color:#00f;font-weight:bold">rdfs</span>:<span style="color:#008000;font-weight:bold">label</span> <span style="color:#b8860b">?label</span> } <span style="color:#a2f;font-weight:bold">LIMIT</span> <span style="color:#666">1</span> |
| </span></span><span style="display:flex;"><span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#080;font-style:italic">## Get zero or one labels for each subject.</span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#666">*</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span> |
| </span></span><span style="display:flex;"><span> <span style="">LATERAL</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">OPTIONAL</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#666">*</span> { <span style="color:#b8860b">?s</span> <span style="color:#00f;font-weight:bold">rdfs</span>:<span style="color:#008000;font-weight:bold">label</span> <span style="color:#b8860b">?label</span> } <span style="color:#a2f;font-weight:bold">LIMIT</span> <span style="color:#666">1</span> |
| </span></span><span style="display:flex;"><span> } |
| </span></span><span style="display:flex;"><span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><h4 id="syntax">Syntax</h4> |
| <p>The <code>LATERAL</code> keyword which takes the graph pattern so far in the group, from |
| the <code>{</code> starting of the current block, and a <code>{ }</code> block afterwards.</p> |
| <h4 id="evaluation">Evaluation</h4> |
| <p><a href="https://afs.github.io/substitute.html">Substituting variables</a> from the LHS into the RHS (with the same restrictions), then executing the pattern, gives the evaluation of <code>LATERAL</code>.</p> |
| <h4 id="variable-assignment">Variable assignment</h4> |
| <p>There needs to be a new syntax restriction: there can no variable introduced by |
| <code>AS</code> (<code>BIND</code>, or sub-query) or <code>VALUES</code> in-scope at the top level of the |
| <code>LATERAL</code> RHS, that is the same name as any |
| <a href="https://www.w3.org/TR/sparql11-query/#variableScope">in-scope</a> variable from |
| the LHS.</p> |
| <p>Such a variable assignment would conflict with the variable being set in |
| variables of the row being joined.</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#080;font-style:italic">## ** Illegal **</span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#666">*</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span> |
| </span></span><span style="display:flex;"><span> <span style="">LATERAL</span> { <span style="color:#a2f;font-weight:bold">BIND</span>( <span style="color:#666">123</span> <span style="color:#a2f;font-weight:bold">AS</span> <span style="color:#b8860b">?o</span>) } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>See <a href="https://www.w3.org/TR/sparql11-query/#sparqlGrammar">SPARQL Grammar note 12</a>.</p> |
| <p>In ARQ, <a href="assignment.html">LET</a> would work. |
| <code>LET</code> for a variable that is bound acts like a filter.</p> |
| <h4 id="variable-scopes">Variable Scopes</h4> |
| <p>In looping on the input, a lateral join makes the bindings of variables in the current row |
| available to the right-hand side pattern, setting their value from the top down.</p> |
| <p>In SPARQL, it is possible to have variables of the same name which are not |
| exposed within a sub-select. These are not lateral-joined to a variable of the |
| same name from the LHS.</p> |
| <p>This is not specific to lateral joins. In</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#666">*</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#b8860b">?s</span> <span style="color:#00f;font-weight:bold">rdf</span>:<span style="color:#008000;font-weight:bold">type</span> :<span style="color:#008000;font-weight:bold">T</span> |
| </span></span><span style="display:flex;"><span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#b8860b">?label</span> { <span style="color:#b8860b">?s</span> <span style="color:#00f;font-weight:bold">rdfs</span>:<span style="color:#008000;font-weight:bold">label</span> <span style="color:#b8860b">?label</span> } |
| </span></span><span style="display:flex;"><span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>the inner <code>?s</code> can be replaced by <code>?z</code> without changing the results because the |
| inner <code>?s</code> is not joined to the outer <code>?s</code> but instead is hidden by the <code>SELECT ?label</code>.</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#666">*</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#b8860b">?s</span> <span style="color:#00f;font-weight:bold">rdf</span>:<span style="color:#008000;font-weight:bold">type</span> :<span style="color:#008000;font-weight:bold">T</span> |
| </span></span><span style="display:flex;"><span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#b8860b">?label</span> { <span style="color:#b8860b">?z</span> <span style="color:#00f;font-weight:bold">rdfs</span>:<span style="color:#008000;font-weight:bold">label</span> <span style="color:#b8860b">?label</span> } |
| </span></span><span style="display:flex;"><span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>The same rule applies to lateral joins.</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#666">*</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#b8860b">?s</span> <span style="color:#00f;font-weight:bold">rdf</span>:<span style="color:#008000;font-weight:bold">type</span> :<span style="color:#008000;font-weight:bold">T</span> |
| </span></span><span style="display:flex;"><span> <span style="">LATERAL</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#b8860b">?label</span> { <span style="color:#b8860b">?s</span> <span style="color:#00f;font-weight:bold">rdfs</span>:<span style="color:#008000;font-weight:bold">label</span> <span style="color:#b8860b">?label</span> } <span style="color:#a2f;font-weight:bold">LIMIT</span> <span style="color:#666">1</span> |
| </span></span><span style="display:flex;"><span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>The inner <code>?s</code> in the <code>SELECT ?label</code> is not the outer <code>?s</code> because the <code>SELECT ?label</code> does not pass out <code>?s</code>. As a sub-query the <code>?s</code> could be any name except |
| <code>?label</code> for the same results.</p> |
| <h3 id="notes">Notes</h3> |
| <p>There is a similarity to filter <code>NOT EXISTS</code>/<code>EXISTS</code> expressed as the non-legal |
| <code>FILTER ( ASK { pattern } )</code> where the variables of the row being filtered are |
| available to “pattern”. This is similar to an SQL |
| <a href="https://en.wikipedia.org/wiki/Correlated_subquery">correlated subquery</a>.</p> |
| <h2 id="sparql-specification-additional-material">SPARQL Specification Additional Material</h2> |
| <h3 id="syntax-1">Syntax</h3> |
| <p><code>LATERAL</code> is added to the SPARQL grammar at rule <code>[[56] GraphPatternNotTriples](https://www.w3.org/TR/sparql11-query/#rGraphPatternNotTriples)</code>. As a syntax form, it is similar to <code>OPTIONAL</code>.</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-ebnf" data-lang="ebnf"><span style="display:flex;"><span><span style="">[56]</span> <span style="color:#a2f;font-weight:bold">GraphPatternNotTriples </span><span style="">::</span><span style="color:#666">=</span> <span style="color:#a2f;font-weight:bold">GroupOrUnionGraphPattern </span>| <span style="color:#a2f;font-weight:bold">OptionalGraphPattern </span>| <span style="color:#a2f;font-weight:bold">LateralGraphPattern </span>| .<span style="">..</span> |
| </span></span><span style="display:flex;"><span><span style="">[57]</span> <span style="color:#a2f;font-weight:bold">OptionalGraphPattern </span><span style="">::</span><span style="color:#666">=</span> <span style="color:#b44">'OPTIONAL'</span> <span style="color:#a2f;font-weight:bold">GroupGraphPattern</span> |
| </span></span><span style="display:flex;"><span>[ ] <span style="color:#a2f;font-weight:bold">LateralGraphPattern </span><span style="">::=</span> <span style="color:#b44">'LATERAL'</span> <span style="color:#a2f;font-weight:bold">GroupGraphPattern</span> |
| </span></span></code></pre></div><h3 id="algebra">Algebra</h3> |
| <p>The new algebra operator is <code>lateral</code> which takes two expressions</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#666">*</span> { |
| </span></span><span style="display:flex;"><span> <span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span> |
| </span></span><span style="display:flex;"><span> <span style="">LATERAL</span> |
| </span></span><span style="display:flex;"><span> { <span style="color:#b8860b">?a</span> <span style="color:#b8860b">?b</span> <span style="color:#b8860b">?c</span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>is translated to:</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-lisp" data-lang="lisp"><span style="display:flex;"><span>(<span style="color:#b8860b">lateral</span> |
| </span></span><span style="display:flex;"><span> (<span style="color:#b8860b">bgp</span> (<span style="color:#b8860b">triple</span> <span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span>)) |
| </span></span><span style="display:flex;"><span> (<span style="color:#b8860b">bgp</span> (<span style="color:#b8860b">triple</span> <span style="color:#b8860b">?a</span> <span style="color:#b8860b">?b</span> <span style="color:#b8860b">?c</span>))) |
| </span></span></code></pre></div><h3 id="evaluation-1">Evaluation</h3> |
| <p>To evaluate <code>lateral</code>:</p> |
| <ul> |
| <li>Evaluate the first argument (left-hand side from syntax) to get a multiset of solution mappings.</li> |
| <li>For each solution mapping (“row”), |
| <ul> |
| <li>inject variable bindings into the second argument</li> |
| <li>Evaluate this pattern</li> |
| <li>Add to results</li> |
| </ul> |
| </li> |
| </ul> |
| <p>Outline:</p> |
| <pre tabindex="0"><code>Definition: Lateral |
| |
| Let Ω be a multiset of solution mappings. We define: |
| |
| Lateral(Ω, P) = { μ | union of Ω1 where |
| foreach μ1 in Ω: |
| pattern2 = inject(pattern, μ1) |
| Ω1 = eval(D(G), pattern2) |
| result Ω1 |
| } |
| </code></pre><p>where <code>inject</code> is the <a href="https://afs.github.io/substitute.html">corrected <code>substitute</code></a> |
| operation.</p> |
| <p>An alternative style is to define Lateral more like “evaluate P such that μ is |
| in-scope” in some way, rather than rely on <code>inject</code> which is a mechanism.</p> |
| <pre tabindex="0"><code>Definition: Evaluation of Lateral |
| |
| eval(D(G), Lateral(P1, P2) = Lateral(eval(D(G), P1), P2) |
| </code></pre> |
| </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> |
| <ul> |
| <li> |
| <ul> |
| <li><a href="#syntax">Syntax</a></li> |
| <li><a href="#evaluation">Evaluation</a></li> |
| <li><a href="#variable-assignment">Variable assignment</a></li> |
| <li><a href="#variable-scopes">Variable Scopes</a></li> |
| </ul> |
| </li> |
| <li><a href="#notes">Notes</a></li> |
| </ul> |
| </li> |
| <li><a href="#sparql-specification-additional-material">SPARQL Specification Additional Material</a> |
| <ul> |
| <li><a href="#syntax-1">Syntax</a></li> |
| <li><a href="#algebra">Algebra</a></li> |
| <li><a href="#evaluation-1">Evaluation</a></li> |
| </ul> |
| </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> |
