[SHACL-API] Scrolling through an rdf:List

[Angelo Frozza]

Hi,

I'm creating a function to test the minimum number of elements in an rdf:List. I am using the SHACL-API to run this function.

I can't use sh:minCount or sh:maxCount because they disregard the existence of duplicate elements in the rdf:List, and in my case study, I can have more than one element with the same value in the rdf:List.

The function code is:

function myMinOccur ($this) {

// Defines an array for the return

var results = [];

// Defines the the IRI of the target node

var propertyName = TermFactory.namedNode("http://www.example.org#coordinates");  

var rest = TermFactory.namedNode("http://www.w3.org/1999/02/22-rdf-syntax-ns#rest");  

var nil = TermFactory.namedNode("http://www.w3.org/1999/02/22-rdf-syntax-ns#nil");   

        // Finds the object defined by the target node

var propertyObject = $data.find($this, propertyName, null) ;

// Navigate the target node graph

        for (var t = propertyObject.next(); t; t = propertyObject.next()) {

// Each instance is a Javascript object

var node = t.object;

var head = node;

var lenght = 0;

// This loop runs thorugh the list and 

// counts how many elements are in the list.

for ( ; node !== nil; ) {

                   lenght++;

                   var next = $data.find(node,rest,null).next();

                   if (!next || next == node) { node = nil; } 

                      else {node = next;} 

        }

// If the list lenght < 2 ($minSize), then it is an outlier.

if (length < 2 ) {

results.push({

value : head 

});

}

}

return results;

}

I have two problems/doubts in this code:

a) the inner loop is apparently looping, that is, it cannot find the end of the list.

b) How do I pass the value of ex:minSize to the function?

The problem in (a) was discussed, but with no solution, here:

https://github.com/linkeddata/rdflib.js/issues/169

I tested the function with the rdflib.js and rdflib-graph.js libraries found at (https://github.com/TopQuadrant/shacl-js) and it worked perfectly.

However, in this test, the loop mentioned in (a) is replaced by length = node.elements.length, which is not supported by the SHACL-API.

Attached are the shape graph and data graph files used in the tests.

The function is found at http://54.201.29.21/shapes/Case_1-Functions_iterator.js.

Best regards,

Angelo

[Ralph TQ [Gmail]]

Angelo

Just a first glance. I noticed a spelling mistake: lenght++;

Ralph Hodgson, @ralphtq

CTO, TopQuadrant, @TopQuadrant

On Feb 27, 2020, at 8:44 AM, Angelo Frozza <fro...@gmail.com> wrote:



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<Case_1-DataGraph.ttl>

<Case_1-ShapeGraph.ttl>

[Angelo Frozza]

Ralph,

True, there was this error.

Thanks.

I already corrected it in the online version of the function.

But the problem of infinite looping continues.

Hugs,

Angelo

Angelo

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[Holger Knublauch]

Hi Angelo,

apologies but this type of very detailed question goes beyond what we can afford to answer for TBC-FE and API users. I hope you understand the commercial pressures.

Having said this I believe a problem is the !== comparison in

var nil = TermFactory.namedNode("http://www.w3.org/1999/02/22-rdf-syntax-ns#nil"

);   
...

for ( ; node !== nil; ) {
    length++;
    var next = $data.find(node,rest,null).next();
    if (!next || next == node) { 
        node = nil; 
    } 
    else {
        node = next;
    } 
}

because the rdf:nil instance delivered by the $data.find is another JS object. Compare by URIs instead.

To pass in ex:minSize, just declare it as

function myMinOccur ($this, $minSize)

and the engine should bind that variable automatically.

Holger

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[Angelo Frozza]

Hi Holger,

Thanks again for the answers, it has been of great help.

I understand the commercial pressures.

But, here I found the best answers, since there is a lack of material on SHACL.

I believe that I finally got to the solution to my problem.

- I rewrote the comparison using the URI, as you indicated:

 for (; node.value! == "http://www.w3.org/1999/02/22-rdf-syntax-ns#nil";) {...}

- $minSize must be declared with sh:parameter in the shape.

I did this and created a ConstraintComponent, removing the restriction from nodeShape.

I leave here my test files, in case anyone else needs it.

The final code of the function is this:

 function myMinOccur ($this, $minSize) {

    // Defines an array for the return
    var results = [];

    // Defines the the IRIs of the target node

    var propertyName = TermFactory.namedNode("http://www.example.org#coordinates");  
    var rest = TermFactory.namedNode("http://www.w3.org/1999/02/22-rdf-syntax-ns#rest");  
    var nil = TermFactory.namedNode("http://www.w3.org/1999/02/22-rdf-syntax-ns#nil");  


    // Finds the object defined by the target node
    var propertyObject = $data.find($this, propertyName, null) ;


    // Navigate the target node graph
    for (var t = propertyObject.next(); t; t = propertyObject.next()) {
       // Each instance is a Javascript object
       var node = t.object;
       var head = node;

       var length = 0;

       // This loop runs thorugh the list and
       // counts how many elements are in the list.

       for ( ; node.value !== "http://www.w3.org/1999/02/22-rdf-syntax-ns#nil"; ) {

            length++;
            var next = $data.find(node,rest,null).next();

            node = next ? next.object : nil; // Get object if triple
       }
       // If the list length < 2 ($minSize), then it is an outlier.
       if (length < $minSize.lex ) {

          results.push({
          value : head
       });
     }
   }
 return results;
}

And the result of the validation was:

[ a            sh:ValidationReport ;
  sh:conforms  false ;
  sh:result    [ a                             sh:ValidationResult ;
                 sh:focusNode                  ex:MyExample_04 ;
                 sh:resultMessage              "Value does not have shape ex:PointShape" ;
                 sh:resultPath                 ex:p_name_3 ;
                 sh:resultSeverity             sh:Violation ;
                 sh:sourceConstraintComponent  sh:NodeConstraintComponent ;
                 sh:sourceShape                []  ;
                 sh:value                      ex:point_4
               ] ;

  sh:result    [ a                             sh:ValidationResult ;
                 sh:focusNode                  ex:point_4 ;
                 sh:resultMessage              "Verify minOccur in coordinates!!!" ;
                 sh:resultPath                 ex:coordinates ;   # Have only one element in rdf:list
                 sh:resultSeverity             sh:Violation ;
                 sh:sourceConstraintComponent  ex:MinOccurConstraintComponent ;
                 sh:sourceShape                []  ;
                 sh:value                      []  
               ]
] .

Hugs,

Angelo

[Holger Knublauch]

Thanks for sharing this solution.

Holger

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