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#505: Added section on Dynamic SHACL, including two examples (#509)
* #505: Added section on Dynamic SHACL, including two examples * Apply suggestions from code review Co-authored-by: Alex Nelson <alexander.nelson@nist.gov> * Apply suggestions from code review Co-authored-by: Ted Thibodeau Jr <tthibodeau@openlinksw.com> * Update shacl12-node-expr/index.html Co-authored-by: David Habgood <dcchabgood@gmail.com> * Update shacl12-node-expr/index.html Co-authored-by: David Habgood <dcchabgood@gmail.com> * Update shacl12-node-expr/index.html Co-authored-by: Ted Thibodeau Jr <tthibodeau@openlinksw.com> --------- Co-authored-by: Alex Nelson <alexander.nelson@nist.gov> Co-authored-by: Ted Thibodeau Jr <tthibodeau@openlinksw.com> Co-authored-by: David Habgood <dcchabgood@gmail.com>
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‎shacl12-node-expr/index.html

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@@ -481,6 +481,7 @@ <h3>Terminology</h3>
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<dfn data-cite="shacl12-core#dfn-conform" data-lt="conform|conforms">conform</dfn>,
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<dfn data-cite="shacl12-core#dfn-conformance-check" data-lt="conformance check">conformance check</dfn>,
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<dfn data-cite="shacl12-core#dfn-failure" data-lt="failure|failures">failure</dfn>,
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<dfn data-cite="shacl12-core#dfn-validation">validation</dfn>,
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<dfn data-cite="shacl12-core#dfn-shacl-instance" data-lt="shacl instance">SHACL instance</dfn>,
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<dfn data-cite="shacl12-core#dfn-shacl-subclass" data-lt="shacl subclass">SHACL subclass</dfn>,
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<dfn data-cite="shacl12-core#dfn-shacl-type" data-lt="shacl type">SHACL type</dfn>,
@@ -557,12 +558,11 @@ <h3>Document Conventions</h3>
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</section>
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</section>
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<section id="getting-started">
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<section id="getting-started" class="informative">
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<h2>Getting started with Node Expressions</h2>
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<p><em>This section is informative.</em></p>
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<p>
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A SHACL <a>shapes graph</a> can declare node expressions as values of various properties where dynamic computation is useful,
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such as <code>sh:targetNode</code>, <code>sh:values</code> and <code>sh:deactivated</code>.
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such as <code>sh:targetNode</code>, <code>sh:values</code>, and <code>sh:deactivated</code>.
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A node expression is represented by an RDF node and can be evaluated to produce a list of <a>output nodes</a>.
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For example, when used at <code>sh:targetNode</code>, a node expression produces the list
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of target nodes of a <a>shape</a>.
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</section>
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<section id="dynamic-shacl">
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<h2>Dynamic SHACL</h2>
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<p>
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This section defines <dfn>Dynamic SHACL</dfn> as a dialect of SHACL that some implementations MAY support.
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</p>
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<p>
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In Dynamic SHACL any <a>parameter</a> of a <a>constraint</a> can be computed using a <a>node expression</a>,
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excluding those that do <em>not</em> allow <a>blank nodes</a> (such as <code>sh:node</code>)
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but including those that take <a>SHACL lists</a> as values (such as <code>sh:class</code>,
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<code>sh:datatype</code>, and <code>sh:in</code>).
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During <a>validation</a>, such <a>node expressions</a> are evaluated in the <a>data graph</a>,
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using the current <a>focus node</a>.
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The resulting <a>nodes</a> will be used as <a>parameters</a> for the <a>constraint</a>.
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</p>
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<section class="informative">
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<h3>Example: Dynamic Minimum Age of Presidents</h3>
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<p>
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As a use case of <a>Dynamic SHACL</a>, assume we want to express that the legal minimum age
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of a president is 18 unless the country is USA, where it is 35.
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</p>
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<aside class="example" title="Example of Dynamic SHACL using a node expression at sh:minInclusive">
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<div class="shapes-graph">
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<div class="turtle">
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ex:PresidentShape
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a sh:NodeShape ;
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sh:targetClass ex:President ;
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sh:property ex:PresidentShape-age ;
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.
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ex:PresidentShape-age
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a sh:PropertyShape ;
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sh:path ex:age ;
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<b>sh:minInclusive [
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shnex:if [
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sparql:eq (
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[ shnex:path ex:country ]
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ex:USA
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)
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]
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shnex:then 35 ;
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shnex:else 18 ;
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]</b> .
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</div>
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<div class="jsonld">
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<pre class="jsonld">
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TODO
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</pre>
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</div>
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</div>
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</aside>
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</section>
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<section class="informative">
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<h3>Example: Dynamic Enumerations</h3>
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<p>
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As a use case of <a>Dynamic SHACL</a>, assume the following <a>data graph</a>.
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</p>
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<aside class="example" title="Example data graph with addresses">
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<div class="data-graph">
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<div class="turtle">
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ex:ArizonaAddress1
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a ex:Address ;
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ex:street "123 John Muir Ave" ;
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ex:country ex:USA ;
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ex:state "AZ" ;
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.
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ex:QueenslandAddress1
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a ex:Address ;
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ex:street "123 Bob Katter Cl" ;
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ex:country ex:Australia ;
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ex:state "QLD" ;
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.
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</div>
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<div class="jsonld">
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<pre class="jsonld">
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TODO
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</pre>
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</div>
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</div>
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</aside>
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<p>
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We want to express that the valid values of <code>ex:state</code> depend on the value of <code>ex:country</code>
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at the given focus node.
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For example, the valid values for country <code>ex:USA</code> would be <code>( "AL" "AK" "AZ" ... )</code>
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while valid values for country <code>ex:Australia</code> would be <code>( "ACT" "NSW" "NT" "QLD" "SA" "TAS" "VIC" "WA" )</code>.
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This fact can be represented as part of the data:
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</p>
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<aside class="example" title="The valid states can be attached to each country">
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<div class="data-graph">
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<div class="turtle">
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ex:Australia
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a ex:Country ;
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ex:stateCode "ACT",
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"NSW",
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"NT",
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"QLD",
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"SA",
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"TAS",
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"VIC",
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"WA" ;
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.
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ex:USA
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a ex:Country ;
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ex:stateCode "AL",
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"AK",
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"AZ",
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"AR" ; # ...
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.
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</div>
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<div class="jsonld">
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<pre class="jsonld">
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TODO
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</pre>
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</div>
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</div>
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</aside>
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<p>
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Using this extra information, we can now define a <code>sh:in</code> constraint using a <a>Path Expression</a>:
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</p>
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<aside class="example" title="Example of Dynamic SHACL using a node expression at sh:in">
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<div class="shapes-graph">
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<div class="turtle">
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ex:Address
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a sh:ShapeClass ;
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sh:property ex:Address-state ;
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.
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ex:Address-state
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a sh:PropertyShape ;
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sh:path ex:state ;
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<b>sh:in [
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shnex:path ( ex:country ex:stateCode )
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]</b> .
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</div>
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<div class="jsonld">
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<pre class="jsonld">
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TODO
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</pre>
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</div>
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</div>
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</aside>
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<p>
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During validation, a Dynamic SHACL engine will evaluate the path expression at <code>sh:in</code>
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and use the resulting nodes as members of the allowed values.
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Thus, when the value of <code>ex:country</code> is <code>ex:USA</code>, it will look up the
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state codes that are linked to <code>ex:USA</code>.
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</p>
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</section>
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</section>
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<section id="security">
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<h2>Security Considerations</h2>
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<p>TODO</p>

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