@shexjs/validator

@shexjs/validator

Validate nodes in an RDF graph against shapes in a ShEx schema.

The validator takes a schema (parsed ShExJ), a data interface (a @shexjs/neighborhood-api implementation over an RDF/JS store, a SPARQL endpoint, a Wikibase…) and a shape map saying which nodes to test against which shapes.

Install

npm install @shexjs/validator

Quick start

const {ShExValidator} = require("@shexjs/validator");
const {ctor: RdfJsDb} = require("@shexjs/neighborhood-rdfjs");
const {Store, Parser} = require("n3");
const base = "http://a.example/";

const schema = require("@shexjs/parser").construct(base).parse(`
<S1> { <p1> . ; <p2> . }`);
const graph = new Store(new Parser({baseIRI: base}).parse(`
<n1> <p1> 1 ; <p2> 2 .
<n2> <p1> 3 ; <p3> 4 . # p3 where <S1> wants p2
`));

const validator = new ShExValidator(schema, RdfJsDb(graph));
const results = validator.validateShapeMap([
  {node: base + "n1", shape: base + "S1"},
  {node: base + "n2", shape: base + "S1"},
]);
results.forEach(r => console.log(r.node, r.status));

http://a.example/n1 conformant
http://a.example/n2 nonconformant

To validate against the schema's start shape, pass the Start sentinel from @shexjs/term as the shape:

const {Start} = require("@shexjs/term");
validator.validateShapeMap([{node: base + "n1", shape: Start}]);

The results

validateShapeMap returns the shape map with each association's status filled in and an appinfo saying why. For the nonconformant n2 above:

{
  "node": "http://a.example/n2",
  "shape": "http://a.example/S1",
  "status": "nonconformant",
  "appinfo": {
    "type": "Failure",
    "node": "http://a.example/n2",
    "shape": "http://a.example/S1",
    "errors": [
      {
        "type": "MissingProperty",
        "property": "http://a.example/p2"
      }
    ],
    "repairs": [
      {
        "type": "NearestBag",
        "cost": 1,
        "arcs": [
          {
            "property": "http://a.example/p2",
            "delta": 1
          }
        ]
      }
    ]
  }
}

errors says what failed; repairs says the cheapest edits that would have made it pass (here: add one <p2> arc). @shexjs/util's errsToSimple renders either as sentences.

Validation proof

A conformant association's appinfo is a proof: which triples matched which constraints. For n1 above:

{
  "type": "ShapeTest",
  "node": "http://a.example/n1",
  "shape": "http://a.example/S1",
  "solution": {
    "type": "EachOfSolutions",
    "solutions": [
      {
        "type": "EachOfSolution",
        "expressions": [
          {
            "type": "TripleConstraintSolutions",
            "predicate": "http://a.example/p1",
            "solutions": [
              {
                "type": "TestedTriple",
                "subject": "http://a.example/n1",
                "predicate": "http://a.example/p1",
                "object": {
                  "value": "1",
                  "type": "http://www.w3.org/2001/XMLSchema#integer"
                }
              }
            ]
          },
          {
            "type": "TripleConstraintSolutions",
            "predicate": "http://a.example/p2",
            "solutions": [
              {
                "type": "TestedTriple",
                "subject": "http://a.example/n1",
                "predicate": "http://a.example/p2",
                "object": {
                  "value": "2",
                  "type": "http://www.w3.org/2001/XMLSchema#integer"
                }
              }
            ]
          }
        ]
      }
    ]
  }
}

See the ShEx primer for validation semantics and ShExV for the results vocabulary.

Choosing a matching engine

The triple expression in a Shape is essentially a fancy regular expression, and the engine that matches it is pluggable (@shexjs/eval-validator-api). shex.js ships two:

• @shexjs/eval-threaded-nerr (default) — exhaustively enumerates the ways the data fails to satisfy a shape's expression;
• @shexjs/eval-simple-1err — stops at the first error.

Select one with the options parameter to the constructor:

new ShExValidator(schema, RdfJsDb(graph), {
  regexModule: require("@shexjs/eval-simple-1err").RegexpModule
});

External shapes

One form of ShEx extensibility is the declaration of external shapes:

<S1> {
  <p1> @<S2>
}
<S2> EXTERNAL

The ShEx specification doesn't say how these are supplied; in shex.js, pass a validateExtern function in the options:

new ShExValidator(schema, RdfJsDb(g), {
  validateExtern: myValidator
});

// (RdfJs.Term, string, ShapeExprValidationContext) -> shapeExprTest
function myValidator (point, shapeLabel, ctx) {
  if (shapeLabel === "http://a.example/S2") {
    const p2z = g.getQuads(point, "http://a.example/p2", null);
    if (p2z.length === 1) {
      return {
        "type": "ShapeTest",
        "node": point.value,
        "shape": "http://a.example/S2",
        "solution": {
          "type": "TripleConstraintSolutions",
          "predicate": "http://a.example/p2",
          "solutions": [
            {
              "type": "TestedTriple",
              "subject": point.value,
              "predicate": "http://a.example/p2",
              "object": p2z[0].object.value
            }
          ]
        }
      };
    }
  }
}

Validating a schema with external shapes and no validateExtern raises:

Error: validating "http://a.example/n2" as EXTERNAL shapeExpr http://a.example/S2 requires a 'validateExtern' option

Testing

Run this package's tests from packages/:

cd .. && npx mocha -C shex-validator/test/Validation-test.js

Selecting tests

Set TESTS to a regular expression matched against test ids, schema and data file names to run a subset:

TESTS='vitals-RESTRICTS' npx mocha -C shex-validator/test/Validation-test.js

Regenerating reference results (REGEN=1)

Validation-test.js compares validation output against the reference results in test/val/ (as mapped by test/val/test-result-map.json). When an intentional change to the validator alters the ShExResults structures, set REGEN=1 to rewrite the reference file of any test whose (canonicalized) result no longer matches, instead of failing the assertion:

TESTS='(ExtendsRepeatedP-pass|2dot_fail-empty-err)' REGEN=1 npx mocha -C shex-validator/test/Validation-test.js

The run reports the regenerated tests as passing; review the rewritten files with git diff (or ediff) and commit the ones that reflect the intended change. Always scope REGEN with TESTS to the tests you mean to regenerate — an unscoped REGEN=1 run will absorb any mismatch, including real regressions. Tests without an entry in test-result-map.json only check conformance status and are unaffected.

Result names

When validating EXTENDS hierarchies, the first result for each extension/subgraph pair carries a "resultName"; identical re-examinations in later partitions emit {"type": "ResultReference", "ref": <resultName>} instead of repeating it. A result name is the focus node followed by a ShExPath expression addressing the extension: a labeled extension by its shape-declaration selector,

<http://a.example/s>@<http://a.example/#B>

an inline extension by a step into the extending shape's EXTENDS list (…@<label>/extends/*[0] — extends selects the list, which is an item of its own in ShExPath, /* steps into it and [0] picks the first out). Only when the same node and extension are validated against a different subgraph is a disambiguating #2, #3, … appended.

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@shexjs/validator is one of the shex.js packages; installing shex pulls in the whole suite, and its README maps them.