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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset='utf-8'>
<title>YARRRML</title>
<script
src='resources/js/respec-w3c-common.js'
class='remove'></script>
<script class='remove'>
var respecConfig = {
localBiblio: {
"DCAT": {
title: "Data Catalog Vocabulary (DCAT) - Version 2",
href: "https://www.w3.org/TR/vocab-dcat/",
status: "W3C Recommendation",
publisher: "W3C",
date: "22 February 2020",
},
"SD": {
title: "SPARQL 1.1 Service Description",
href: "https://www.w3.org/TR/sparql11-service-description/",
status: "W3C Recommendation",
publisher: "W3C",
date: "21 March 2013",
},
"D2RQ": {
title: "The D2RQ Mapping Language",
href: "https://d2rq.org/d2rq-language",
status: "Unofficial Draft",
authors: [
"Richard Cyganiak",
"Chris Bizer",
"Jörg Garbers",
"Oliver Maresch",
"Christian Becker"
],
publisher: "Freie Universität Berlin - DERI",
date: "12 March 2012",
},
"FnO": {
title: "The Function Ontology",
href: "https://fno.io/spec/",
status: "Unofficial Draft",
authors: [
"Ben De Meester",
"Anastasia Dimou"
],
publisher: "IDLab - imec - Ghent University",
date: "10 November 2021",
},
"RMLT": {
title: "Target in RML",
href: "https://rml.io/specs/rml-target",
status: "Unofficial Draft",
authors: [
"Dylan Van Assche",
"Anastasia Dimou"
],
publisher: "IDLab - imec - Ghent University",
date: "18 May 2021",
},
"RMLStar": {
title: "Star in RML",
href: "https://w3id.org/kg-construct/rml-star",
status: "Unofficial Draft",
authors: [
"Ana Iglesias-Molina",
"Julián Arenas-Guerrero",
"Thomas Delva",
"David Chaves-Fraga",
"Anastasia Dimou"
],
publisher: "W3C CG in KGC",
date: "05 May 2022",
},
"RML": {
title: "RDF Mapping Language (RML)",
href: "https://rml.io/specs/rml/",
status: "Unofficial Draft",
authors: [
"Anastasia Dimou",
"Miel Vander Sande"
],
publisher: "IDLab - imec - Ghent University",
date: "October 2020",
},
"DataIO": {
title: "DataIO",
href: "https://rml.io/specs/dataio",
status: "Unofficial Draft",
authors: [
"Dylan Van Assche",
"Anastasia Dimou"
],
publisher: "IDLab - imec - Ghent University",
date: "18 May 2021",
},
},
specStatus: "unofficial",
editors: [{
name: "Dylan Van Assche",
url: "https://dylanvanassche.be/",
mailto: "[email protected]",
company: 'Ghent University - IDLab, imec',
},{
name: "Ben De Meester",
url: "https://ben.de-meester.org",
mailto: "[email protected]",
company: 'Ghent University - IDLab, imec',
},{
name: "Pieter Heyvaert",
url: "https://pieterheyvaert.com",
mailto: "[email protected]",
company: 'Ghent University - IDLab, imec',
},{
name: "Anastasia Dimou",
url: "https://www.kuleuven.be/wieiswie/en/person/00142590",
mailto: "[email protected]",
company: 'KULeuven - DTAI-EAVISE',
},{
name: "David Chaves-Fraga",
url: "https://davidchavesfraga.com",
mailto: "[email protected]",
company: 'Universidad Politécnica de Madrid - OEG',
},{
name: "Ana Iglesias-Molina",
url: "https://oeg.fi.upm.es/index.php/es/phdstudents/393-aiglesias/index.html",
mailto: "[email protected]",
company: 'Universidad Politécnica de Madrid - OEG',
}],
// edDraftURI: "http://some.github.repo",
shortName: "yarrrml",
previousURI: "https://w3id.org/kg-construct/yarrrml/20230126/index.html",
previousPublishDate: "2023-01-26",
previousMaturity: "unofficial",
canonicalURI: "https://w3id.org/kg-construct/yarrrml",
logos: [{
src: "resources/images/logo.png",
href: "https://w3id.org/kg-construct/yarrrml",
alt: "YARRRML",
width: 164
}],
otherLinks: [
{
key: "This Version",
data: [{
value: "https://w3id.org/kg-construct/yarrrml/%thisDate%/",
href: "https://w3id.org/kg-construct/yarrrml/%thisDate%/"
}]
},
{
key: "Previous Version",
data: [{
value: "https://w3id.org/yarrrml/spec/%prevDate%/",
href: "https://w3id.org/yarrrml/spec/%prevDate%/"
}]
},
{
key: "Website",
data: [{
value: "https://w3id.org/kg-construct/yarrrml",
href: "https://w3id.org/kg-construct/yarrrml"
}]
}
],
};
</script>
<style>
.nanotabs { text-align:left; width:500px; margin:20px auto 0; }
.nanotabs { margin:20px 0 60px; }
.nanotabs li { float:left; list-style:none; }
.nanotabs li a { display:block; padding:4px 6px; background:#DDD; color:#333; font:bold 11pt Verdana; text-decoration:none; }
.nanotabs li a:hover { background:#EEE; color:#000; }
.nanotabs li a.selected { background:#555; color:#FFF; }
/*.nanotabs div {clear:left; display:none; background:#EEE; border-top:1px solid #555; border-bottom:1px solid #888; padding:8px; *padding-top:4px; letter-spacing:1px; }*/
</style>
</head>
<body>
<section id='abstract'>
<p>
YARRRML (pronounced /jɑɹməl/) is a human readable text-based representation for declarative generation rules.
It is a subset of [[YAML]],
a widely used data serialization language designed to be human-friendly.
</p>
</section>
<section id='sotd'>
</section>
<section>
<h2>Terminology</h2>
<dl>
<dt><dfn>subject</dfn></dt>
<dd>the subject of an RDF triple</dd>
<dt><dfn>predicate</dfn></dt>
<dd>the predicate of an RDF triple</dd>
<dt><dfn>object</dfn></dt>
<dd>the object of an RDF triple</dd>
<dt><dfn>class</dfn></dt>
<dd>the type of an entity</dd>
<dt><dfn>datatype</dfn></dt>
<dd>the type of a literal value</dd>
<dt><dfn>reference</dfn></dt>
<dd>the reference to a data fraction in a data source</dd>
<dt><dfn>function</dfn></dt>
<dd>a programmatic function that takes 0 or more input parameters and returns a single result</dd>
</dl>
</section>
<section>
<h2>Profiles</h2>
<p>
This specification includes the following main profiles for tools that process YARRRML documents:
</p>
<ul>
<li>R2RML: applies the semantics specified by [[R2RML]];</li>
<li>RML: applies the semantics specified by [[RML]]; and</li>
<li>RMLT: applies the semantics specified by [[RMLT]].</li>
<li>RMLStar: applies the semantics specified by [[RMLStar]].</li>
</ul>
<p>
These profiles can be extended with additional profiles, which cannot be used on their own:
</p>
<ul>
<li>FORMATS: applies the semantics specified by the <a href="http://w3.org/ns/formats">W3C Formats namespace</a>.</li>
<li>COMP: applies the semantics specified by the <a href="http://semweb.mmlab.be/ns/rml-compression#">Compression namespace</a>.</li>
<li>VOID: applies the semantics specified by [[VoID]];</li>
<li>FnO: applies the semantics specified by [[FnO]];</li>
<li>DCAT: applies the semantics specified by [[DCAT]];</li>
<li>D2RQ: applies the semantics specified by [[D2RQ]];</li>
<li>SD: applies the semantics specified by SD ([[sparql11-service-description]]); and</li>
<li>CSVW: applies the semantics specified by CSVW ([[csv2rdf]]).</li>
<li>WOT: applies the semantics specified by WoT Thing Description and WoT Security ([[wot-thing-description]], [[wot-security]])</li>
</ul>
</section>
<section>
<h2>Base IRI</h2>
<p>
A base IRI can be defined.
This IRI will be used for the creation of the IRIs of the term maps and sources of the [R2]RML rules.
</p>
<p>
A base IRI can be added by adding key <code>base</code> with as value the IRI itself to the root of the document.
In the following example the base IRI is set to <code>http://mybaseiri.com#</code>.
</p>
<pre id="example-base-iri" class="nohighlight example" title="base IRI">
base: http://mybaseiri.com#
</pre>
</section>
<section>
<h2>Prefixes and namespaces</h2>
<p>
A set of prefixes and namespaces are predefined by default in every YARRRML document.
There are the same as the predefined prefixes for <a href="https://www.w3.org/2011/rdfa-context/rdfa-1.1">RDFa</a>.
</p>
<p>
Custom prefixes can be added by adding the collection <code>prefixes</code> to the root of the document.
Each combination of a prefix and namespace is added to this collection as a key-value pair.
In the following example two prefixes are defined: <code>ex</code> and <code>test</code>.
</p>
<pre id="example-custom-prefixes" class="nohighlight example" title="custom prefixes">
prefixes:
ex: http://www.example.com
test: http://www.test.com
</pre>
</section>
<section>
<h2>Authors</h2>
<p>
The authors of the YARRRML rules can be added via the key <code>authors</code>.
The value is an array with an object for each author.
Each author can have the following keys:
</p>
<dl>
<dt><dfn>name</dfn></dt>
<dd>the name of the author</dd>
<dt><dfn>email</dfn></dt>
<dd>the email of the author</dd>
<dt><dfn>website</dfn></dt>
<dd>the website of the author</dd>
</dl>
<p>
In the following example two authors are defined.
</p>
<div id="tabs-author" class="nanotabs">
<ul>
<li><a href="#tab-author-1" class="selected">YARRRML</a></li>
<li><a href="#tab-author-2">RML</a></li>
</ul>
<div id="tab-author-1">
<pre id="example-author-yarrrml" class="nohighlight example" title="mapping with multiple authors">
authors:
- name: John Doe
email: [email protected]
- name: Jane Doe
website: https://janedoe.com
</pre>
</div>
<div id="tab-author-2">
<pre id="example-author-rml" class="example" title="mapping with multiple authors">
:Rules a void:Dataset;
void:exampleResource <#TM>; # linking all Triples Maps
dcterms:contributor [
a foaf:Person;
rdfs:label "John Doe";
foaf:mbox <mailto:[email protected]>
], [
a foaf:Person;
rdfs:label "Jane Doe";
foaf:homepage <https://janedoe.com>
].
</pre>
</div>
</div>
<p>
A string template exists that provides a shortcut version: <code>name <email> (website)</code>.
In the following example the same two authors are defined.
</p>
<div id="tabs-author-sc" class="nanotabs">
<ul>
<li><a href="#tab-author-sc-1" class="selected">YARRRML</a></li>
<li><a href="#tab-author-sc-2">RML</a></li>
</ul>
<div id="tab-author-sc-1">
<pre id="example-author-yarrrml-sc" class="nohighlight example" title="mapping with multiple authors">
authors:
- John Doe <[email protected]>
- Jane Doe (https://janedoe.com)
</pre>
</div>
<div id="tab-author-sc-2">
<pre id="example-author-rml-sc" class="example" title="mapping with multiple authors">
:Rules a void:Dataset;
void:exampleResource <#TM>; # linking all Triples Maps
dcterms:contributor [
a foaf:Person;
rdfs:label "John Doe";
foaf:mbox <mailto:[email protected]>
], [
a foaf:Person;
rdfs:label "Jane Doe";
foaf:homepage <https://janedoe.com>>
].
</pre>
</div>
</div>
<p>
In the case that authors have a WebID, it can be used instead of providing the name, email and so on.
In the following example the same two authors are added via their WebIDs.
</p>
<div id="tabs-author-webid" class="nanotabs">
<ul>
<li><a href="#tab-author-webid-1" class="selected">YARRRML</a></li>
<li><a href="#tab-author-webid-2">RML</a></li>
</ul>
<div id="tab-author-webid-1">
<pre id="example-author-yarrrml-webid" class="nohighlight example" title="mapping with multiple authors">
authors:
- http://johndoe.com/#me
- http://janedoe.com/#me
</pre>
</div>
<div id="tab-author-webid-2">
<pre id="example-author-rml-webid" class="example" title="mapping with multiple authors">
:Rules a void:Dataset;
void:exampleResource <#TM>; # linking all Triples Maps
dcterms:contributor <http://johndoe.com/#me>,
<http://janedoe.com/#me>.
</pre>
</div>
</div>
<p>
In all the above cases when there is only author, an array is not needed.
In the following example one author is defined.
</p>
<div id="tabs-author-sc-single" class="nanotabs">
<ul>
<li><a href="#tab-author-sc-single-1" class="selected">YARRRML</a></li>
<li><a href="#tab-author-sc-single-2">RML</a></li>
</ul>
<div id="tab-author-sc-single-1">
<pre id="example-author-yarrrml-sc-single" class="nohighlight example" title="mapping with multiple authors">
authors: John Doe <[email protected]>
</pre>
</div>
<div id="tab-author-sc-single-2">
<pre id="example-author-rml-sc-single" class="example" title="mapping with multiple authors">
:Rules a void:Dataset;
void:exampleResource <#TM>; # linking all Triples Maps
dcterms:contributor [
a foaf:Person;
rdfs:label "John Doe";
foaf:mbox <mailto:[email protected]>
].
</pre>
</div>
</div>
</section>
<section>
<h2>Template</h2>
<p>
A template contains 0 or more constant strings and 0 or more references to data in a data.
References are prefixed with <code>$(</code> and suffixed with <code>)</code>.
For example, <code>foo</code> is a template with one constant string.
<code>$(id)</code> is a template with one reference to <code>id</code>.
<code>foo-$(id)</code> is a template with one constant string <code>foo-</code> and one reference to <code>id</code>.
</p>
</section>
<section>
<h2>Data sources</h2>
<p>
The data sources are defined in the <code>sources</code> collection in the root of the document.
Each source is added to this collection via a key-value pair.
The key has to be unique for every source.
The value is a collection with the keys described below.
</p>
<section>
<h2>Keys</h2>
<dl>
<dt><dfn>type</dfn></dt>
<dd>Type of the data source.<br />
Required profiles: RML. <br />
Datatype: string.
</dd>
<dt><dfn>access</dfn></dt>
<dd>Local or remote location of the data source. <br />
Required profiles: RML. <br />
Datatype: string.
</dd>
<dt><dfn>credentials</dfn></dt>
<dd>Credentials required to access the data source.<br />
Required profiles: RML. <br />
Datatype: collection.
</dd>
<dt><dfn>queryFormulation</dfn></dt>
<dd>Query formulation used to query the data source. <br />
Required profiles: RML or R2RML. <br />
Datatype: string.
</dd>
<dt><dfn>query</dfn></dt>
<dd>Query to execute on the data source to retrieve the desired data. <br />
Required profiles: RML or R2RML. <br />
Datatype: string.
</dd>
<dt><dfn>encoding</dfn></dt>
<dd>Encoding used by the data. <br />
Required profiles: RML and CSVW. <br />
Datatype: string.
</dd>
<dt><dfn>delimiter</dfn></dt>
<dd>Delimiter to separate fields in a record. <br />
Required profiles: RML and CSVW. <br />
Datatype: string.
</dd>
<dt><dfn>contentType</dfn></dt>
<dd>Content type to expect expressed as MIME types. <br />
Required profiles: RML and WOT. <br />
Datatype: string.
</dd>
<dt><dfn>operationType</dfn></dt>
<dd>Indicates the operation type of the Web of Things description. <br />
Required profiles: RML and WOT. <br />
Datatype: string.
</dd>
<dt><dfn>referenceFormulation</dfn></dt>
<dd>Reference formulation used to access the data retrieved from the data source. <br />
Required profiles: RML. <br />
Datatype: string.
</dd>
<dt><dfn>iterator</dfn></dt>
<dd>Path to the records over which to iterate. <br />
Required profiles: RML. <br />
Datatype: string.
</dd>
</dl>
</section>
<section>
<h2>Type</h2>
<p>
This key's value describes what type of data source is used,
so that the correct way of connecting to the data source can be determined.
By default a local file is assumed when the <code>access</code> value is a path such as <code>file.json</code>.
The value of type is then implicitly <code>localfile</code>.
By default a remote file is assumed and retrieved via an HTTP GET when a URL is given such as <code>http://example.org/file.json</code>.
The value of type is then implicitly <code>remotefile</code>.
The following values are supported:
</p>
<table>
<tr><th>Data source type</th><th>Value</th><th>Required profiles</th></tr>
<tr><td><a href="https://www.oracle.com/database/technologies/">Oracle Database</a></td><td>oracle</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://www.mysql.com/">MySQL</a></td><td>mysql</td><td>RML and D2RQ</td></tr>
<tr><td><a href="http://hsqldb.org/">HSQLDB</a></td><td>hsql</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://www.postgresql.org/">PostgreSQL</a></td><td>postgresql</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://www.ibm.com/products/db2-database">IBM DB2</a></td><td>db2</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://www.ibm.com/products/informix">IBM Informix</a></td><td>informix</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://www.actian.com/data-management/actian-x-hybrid-rdbms/">Ingres</a></td><td>ingres</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://www.sap.com/products/sybase-ase.html">SAP Adaptive Server Enterprise</a></td><td>sapase</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://www.sap.com/products/sql-anywhere.html">SAP SQL Anywhere</a></td><td>sapsqlanywhere</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://firebirdsql.org/">Firebird</a></td><td>firebird</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://www.microsoft.com/en-gb/sql-server/sql-server-2019">Microsoft SQL Server</a></td><td>mssqlserver</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://virtuoso.openlinksw.com/">Virtuoso</a></td><td>virtuoso</td><td>RML and D2RQ</td></tr>
<tr><td><a href="https://www.w3.org/WoT/">Web of Things</a></td><td>wot</td><td>RML and WOT</td></tr>
<tr><td>SPARQL endpoint</td><td>sparql</td><td>RML and SD</td></tr>
<tr><td>Local file</td><td>localfile</td><td>RML</td></tr>
<tr><td>Remote file</td><td>remotefile</td><td>RML</td></tr>
</table>
<div class="note">
<p>
R2RML rules do not include this information:
it is supplied directly to the used R2RML processor.
Also, it does not support SPARQL endpoints, local files, and remote files.
</p>
</div>
</section>
<section>
<h2>Access</h2>
<p>
This key's value describes where the data source can be accessed.
Examples are <code>file.json</code> and <code>http://example.org/my/db</code>.
</p>
</section>
<section>
<h2>Query formulation</h2>
<p>
Query formulations define what type of query is used query to a data source.
This key's supported values are the same as the values for the type,
together with the additional values below.
Therefore, if only a type is provided the query formulation is implicitly the same.
But if you want for example to use a MySQL query with an Oracle Database,
then you need to specify both the type and the query formulation.
</p>
<p>
In the case of SPARQL endpoints, defined by the value <code>sparql</code> for type,
the query formulation is by default <code>sparql11</code>: the data sources are queried
via a <a href="https://www.w3.org/TR/sparql11-query/">SPARQL 1.1 query</a>.
</p>
<table>
<tr><th>Query formulation</th><th>Value</th><th>Required profiles</th></tr>
<tr><td><a href="https://www.w3.org/TR/sparql11-query/">SPARQL 1.1 query</a> (default for SPARQL endpoint)</td><td>sparql11</td><td>RML and SD</td></tr>
<tr><td><a href="https://en.wikipedia.org/wiki/SQL:2008">SQL:2008</a></td><td>sql2008</td><td>RML and D2RQ, or R2RML</td></tr>
<tr><td><a href="https://en.wikipedia.org/wiki/SQL:2011">SQL:2011</a></td><td>sql2011</td><td>RML and D2RQ, or R2RML</td></tr>
<tr><td><a href="https://en.wikipedia.org/wiki/SQL:2016">SQL:2016</a></td><td>sql2016</td><td>RML and D2RQ, or R2RML</td></tr>
</table>
</section>
<section>
<h2>Query</h2>
<p>
This key's value is a query that conforms the selected query formulation.
For example, if the query formulation is <code>mysql</code>, then
the value of <code>query</code> needs to be a valid MySQL query.
</p>
</section>
<section>
<h2>Reference formulation</h2>
<p>
Reference formulations define how to access the data retrieved from the data source.
For example, this retrieved data can be query results coming from a database or
a JSON file on the local file system.
The value of this key is a string.
This key's supported values are.
</p>
<table>
<tr><th>Reference formulation</th><th>Value</th><th>Required profiles</th></tr>
<tr><td>CSV (tables with columns and rows)</td><td>csv</td><td>RML</td></tr>
<tr><td><a href="https://goessner.net/articles/JsonPath/">JSONPath</a></td><td>jsonpath</td><td>RML</td></tr>
<tr><td><a href="https://www.w3.org/TR/xpath/">XPath</a></td><td>xpath</td><td>RML</td></tr>
<tr><td><a href="https://www.w3.org/TR/xquery/">XQuery</a></td><td>xquery</td><td>RML</td></tr>
</table>
</section>
<section>
<h2>Iterator</h2>
<p>
This key's value defines what records are processed.
It has to conform to the selected reference formulation.
</p>
<p>
Consider the following JSON example with an array of two people.
One person is one record.
</p>
<pre class="hljs javascript">
{
"people": [
{...},
{...}
]
}
</pre>
<p>
To iterate over all the people,
the iterator is <code>$.people[*]</code> when using <code>jsonpath</code> as a reference formulation.
If no iterator is provided,
it is unclear what the records are.
</p>
</section>
<section>
<h2>Delimiter</h2>
<p>
This key's value defines the delimiter when working with CSV files.
The default is <code>,</code>.
</p>
</section>
<section>
<h2>Encoding</h2>
<p>
This key's value defines the encoding of the retrieved data.
The default is <code>utf-8</code>.
</p>
</section>
<section>
<h2>Credentials</h2>
<p>
Credentials are provided when accessing a data source requires authentication.
This key's value is a collection with the keys described below.
</p>
<dl>
<dt><dfn>username</dfn></dt>
<dd>User name required to access the data source. <br />
Required profiles: RML and D2RQ.
</dd>
<dt><dfn>password</dfn></dt>
<dd>Password required to access the data source.<br />
Required profiles: RML and D2RQ.
</dd>
</dl>
</section>
<section>
<h2>Content type</h2>
<p>This key's value defines the content type of the retrieved data with a MIME type.</p>
</section>
<section>
<h2>Operation type</h2>
<p>This key's value defines the operation type for the Web of Things description.</p>
<table>
<tr><th>Operation</th><th>Value</th><th>Operation type</th></tr>
<tr><td>Retrieve data from Web API or stream</td><td><code>read</code></td><td><code>td:readproperty</code></td></tr>
<tr><td>Push data to Web API or stream</td><td><code>write</code></td><td><code>td:writeproperty</code></td></tr>
</table>
</section>
<section>
<h2>Security</h2>
<p>Web of Things Security description to describe how authentication
should be performed againast a Web API or stream when accessing its data.</p>
<table>
<tr><th>Security</th><th>Value</th><th>Web of Things Security scheme</th></tr>
<tr><td>Security through API key</td><td><code>apikey</code></td><td><code>wotsec:APISecurityScheme</code></td></tr>
</table>
<dl>
<dt><dfn>type</dfn></dt>
<dd>Security scheme to apply.<br />
Required profiles: RML and WOT. <br />
</dd>
<dt><dfn>in</dfn></dt>
<dd>Where to store the security information when performing authentication against a Web API or stream.<br />
Required profiles: RML and WOT. <br />
</dd>
<dt><dfn>name</dfn></dt>
<dd>Name of the property holding the private security information such as API key.<br />
Required profiles: RML and WOT. <br />
</dd>
<dt><dfn>value</dfn></dt>
<dd>Value of the property holding the private security information such as API key.<br />
Required profiles: RML and WOT. <br />
</dd>
</dl>
</section>
<section>
<h2>Query formulation vs reference formulation</h2>
<img src="resources/images/query-vs-reference-formulations.jpeg" alt="Sequence diagram showing difference between query and reference formulation">
<p>
In the figure above, you find a sequence diagram showing at what point the query and query formulation are used and
a what point the iterator and reference formulation are used.
The component "Processor" represents the software application that executes the converted YARRRML rules,
e.g., RML rules.
For clarity, this conversion is not included in the figure.
The processor gets the <code>type</code> and <code>access</code> from the YARRRML rules.
It uses this information to create a connection with the data source.
Next, the processor gets the <code>query formulation</code> and <code>query</code>.
It uses this information to query the desired data from the data source,
making use of the earlier created connection.
Once the data is retrieved the connection is closed.
The processor gets the <code>reference formulation</code> and <code>iterator</code>.
It uses this information to iterate over the retrieved data.
</p>
<img src="resources/images/query-vs-reference-formulations-example.jpeg" alt="Sequence diagram showing difference between query and reference formulation for a SPARQL endpoint">
<p>
In the figure above, you find a sequence diagram showing an example of
the use of query, query formulation, iterator, and reference formulation.
The data source is a SPARQL endpoint, available at <code>http://example.org/sparql</code>,
which is queried using a SPARQL 1.1 query.
The query formulation is <code>sparql11</code> and
the query is <code>SELECT * WHERE{?s ?p ?o}</code>
The result is an XML document which is iterated upon using the iterator <code>/sparql/results/result</code>
that conforms to the XPath specification.
</p>
</section>
<section>
<h2>Examples</h2>
<p>
In the following example a single data source is defined <code>person-source</code>.
</p>
<div id="tabs-1" class="nanotabs">
<ul>
<li><a href="#tab1-1" class="selected">YARRRML</a></li>
<li><a href="#tab1-2">RML</a></li>
</ul>
<div id="tab1-1">
<pre id="example-ds1-yarrrml" class="example" title="one data source">
sources:
person-source:
access: data/person.json
referenceFormulation: jsonpath
iterator: $
</pre>
</div>
<div id="tab1-2">
<pre id="example-ds1-rml" class="example" title="one data source">
<#LogicalSource> a rml:LogicalSource;
rml:source "data/person.json";
rml:referenceFormulation ql:JSONPath;
rml:iterator "$".
</pre>
</div>
</div>
<p>
A shortcut version of this example looks as follows.
</p>
<div id="tabs-2" class="nanotabs">
<ul>
<li><a href="#tab2-1" class="selected">YARRRML</a></li>
<li><a href="#tab2-2">RML</a></li>
</ul>
<div id="tab2-1">
<pre id="example-ds1-sc" class="example" title="one data source using shortcuts">
sources:
person-source: [data/person.json~jsonpath, $]
</pre>
</div>
<div id="tab2-2">
<pre id="example-ds1-sc-rml" class="example" title="one data source using shortcuts">
<#LogicalSource> a rml:LogicalSource;
rml:source "data/person.json";
rml:referenceFormulation ql:JSONPath;
rml:iterator "$".
</pre>
</div>
</div>
<p>
The collection is replaced with an array where
the first element contains the value for <code>access</code> appended with the <code>~</code> and the value for <code>referenceFormulation</code>, and
the second element contains the iterator.
</p>
<p>
The following mapping access a SQL database and select the required data via a query.
</p>
<div id="tabs-3" class="nanotabs">
<ul>
<li><a href="#tab3-1" class="selected">YARRRML</a></li>
<li><a href="#tab3-2">RML</a></li>
</ul>
<div id="tab3-1">
<pre id="example-db-yarrrrml" class="example" title="mapping with database as source">
mapping:
person:
sources:
access: http://localhost/example
type: mysql
credentials:
username: root
password: root
queryFormulation: sql2008
query: |
SELECT DEPTNO, DNAME, LOC,
(SELECT COUNT(*) FROM EMP WHERE EMP.DEPTNO=DEPT.DEPTNO) AS STAFF
FROM DEPT;
referenceFormulation: csv
</pre>
</div>
<div id="tab3-2">
<pre id="example-db-rml" class="example" title="mapping with database as source">
<#TriplesMap> a rr:TriplesMap;
rml:logicalSource [
a rml:LogicalSource;
rml:source <#DataSource>;
rr:sqlVersion rr:SQL2008;
rml:query "SELECT DEPTNO, DNAME, LOC,
(SELECT COUNT(*) FROM EMP WHERE EMP.DEPTNO=DEPT.DEPTNO) AS STAFF
FROM DEPT;";
rml:referenceFormulation ql:CSV
].
<#DataSource> a d2rq:Database;
d2rq:jdbcDSN "jdbc:mysql://localhost/example";
d2rq:jdbcDriver "com.mysql.jdbc.Driver";
d2rq:username "root";
d2rq:password "root" .
</pre>
</div>
</div>
</section>
</section>
<section>
<h2>Targets</h2>
<section>
<h2>Keys</h2>
<dl>
<dt><dfn>type</dfn></dt>
<dd>Type of the target.<br />
Required profiles: RMLT. <br />
Datatype: string.
</dd>
<dt><dfn>access</dfn></dt>
<dd>Local or remote location of the target.<br />
Required profiles: RMLT. <br />
Datatype: string.
</dd>
<dt><dfn>serialization</dfn></dt>
<dd>Serialization format to use when exporting to the target.<br />
Required profiles: RMLT and FORMATS. <br />
Datatype: string.
</dd>
<dt><dfn>ompression</dfn></dt>
<dd>Compression algorithm to use when exporting to the target.<br />
Required profiles: RMLT and COMP. <br />
Datatype: string.
</dd>
</dl>
</section>
<section>
<h2>Type</h2>
<p>This key's value describes what type of target is used, so that the correct way
of accessing to the target can be determined. By default a local file is assumed
when the <code>access</code> value is a path such as file.nq. The value of type is
then implicitly <code>localfile</code>. The following values are supported:</p>
<table>
<tr><th>Target type</th><th>Value</th><th>Required profiles</th></tr>
<tr><td>SPARQL endpoint</td><td><code>sparql</code></td><td>RML, RMLT and SD</td></tr>
<tr><td>Local file</td><td><code>localfile</code></td><td>RML, RMLT and VOID/DCAT</td></tr>
</table>
</section>
<section>
<h2>Access</h2>
<p>This key's value describes where the target can be accessed. Example: <code>file.nq</code>. </p>
</section>
<section>
<h2>Serialization</h2>
<p>This key's value is the serialization format that should be used to serialize
the RDF when exporting to the target. By default, the serialization format is N-Quads
[[DataIO]]. The supported serialization formats are listed by the
<a href="http://w3.org/ns/formats">W3C Formats namespace</a>. </p>
<table>
<tr><th>Serialization format</th><th>Value</th></tr>
<tr><td>JSON-LD</td><td>jsonld</td></tr>
<tr><td>N3</td><td>n3</td></tr>
<tr><td>N-Triples</td><td>ntriples</td></tr>
<tr><td>N-Quads</td><td>nquads</td></tr>
<tr><td>LD Patch</td><td>ldpatch</td></tr>
<tr><td>microdata</td><td>microdata</td></tr>
<tr><td>OWL XML Serialization</td><td>owlxml</td></tr>
<tr><td>OWL Functional Syntax</td><td>owlfunctional</td></tr>
<tr><td>OWL Manchester Syntax</td><td>owlmanchester</td></tr>
<tr><td>POWDER</td><td>powder</td></tr>
<tr><td>POWDER-S</td><td>powder-s</td></tr>
<tr><td>PROV-N</td><td>prov-n</td></tr>
<tr><td>PROV-XML</td><td>prov-xml</td></tr>
<tr><td>RDFa</td><td>rdfa</td></tr>
<tr><td>RDF/JSON</td><td>rdfjson</td></tr>
<tr><td>RDF/XML</td><td>rdfxml</td></tr>
<tr><td>RIF XML Syntax</td><td>rifxml</td></tr>
<tr><td>SPARQL Results in XML</td><td>sparqlxml</td></tr>
<tr><td>SPARQL Results in JSON</td><td>sparqljson</td></tr>
<tr><td>SPARQL Results in CSV</td><td>sparqlcsv</td></tr>
<tr><td>SPARQL Results in TSV</td><td>sparqltsv</td></tr>
<tr><td>Turtle</td><td>turtle</td></tr>
<tr><td>TriG</td><td>trig</td></tr>
</table>
</section>
<section>
<h2>Compression</h2>
<p>Compression defines which compression algorithm should be applied when exporting
to a target. By default, no compression algorithm is applied [[DataIO]]. The supported
compression algorithms are listed by the <a href="http://semweb.mmlab.be/ns/rml-compression#">
Compression namespace</a>. </p>
<table>
<tr><th>Compression algorithm</th><th>Value</th></tr>
<tr><td>GZip</td><td>gzip</td></tr>
<tr><td>Zip</td><td>zip</td></tr>
<tr><td>TarGZip</td><td>targzip</td></tr>
<tr><td>TarXz</td><td>tarxz</td></tr>
</table>
</section>
<section>