@shexjs/shape-path-query

Query RDF data by pointing at schema elements: a ShapePath expression selects constraints in a ShEx schema (shape-path-core), and shapePathQuery answers with the terms those constraints matched when the data validated — XPath for the schema, results from the graph.

Install

npm install @shexjs/shape-path-query

Quick start

const Fs = require("fs");
const Path = require("path");
const {Store, Parser} = require("n3");
const Sp = require("shape-path-core");
const {ctor: RdfJsDb} = require("@shexjs/neighborhood-rdfjs");
const {shapePathQuery} = require("@shexjs/shape-path-query");

// the Issue example that ships with shape-path-core
const schema = JSON.parse(Fs.readFileSync(Path.join(Sp.examples, "issue/Issue.json"), "utf8"));
const turtle = Fs.readFileSync(Path.join(Sp.examples, "issue/Issue2.ttl"), "utf8");

// 1. a ShapePath picks schema elements: the <p:href> constraint in <#DiscItem>
const yy = {base: new URL("http://project.example/schema"), prefixes: {}};
const pathExpr = new Sp.Parser.ShapePathParser(yy).parse(
  "@<http://project.example/schema#DiscItem>~<http://project.example/ns#href>"
);
const nodeSet = pathExpr.evalPathExpr([schema], new Sp.Ast.EvalContext(schema));

// 2. validate, and answer with what those elements matched in the data
const graph = new Store(new Parser({baseIRI: "http://project.example/"}).parse(turtle));
shapePathQuery(schema, nodeSet, RdfJsDb(graph),
  [{node: "http://instance.example/project1/Issue2",
    shape: "http://project.example/schema#Issue"}]
).then(terms => console.log(terms));

[ 'http://instance.example/project1/img1.jpg' ]

shapePathQuery(schema, nodeSet, db, shapeMap) → Promise<terms[]>

• schema — a ShExJ schema (@types/shexj shaped);
• nodeSet — schema elements selected by evalPathExpr (they are annotated in place with ShExMap variable bindings — that's the mechanism: the ShapePath aims the query, ShExMap captures the matches);
• db — a @shexjs/neighborhood-api implementation, e.g. @shexjs/neighborhood-rdfjs over your graph;
• shapeMap — which node/shape pairs to validate (a parsed shape map).

Returns the data terms the selected schema elements matched, one entry per binding; throws if the shape map doesn't validate.

From the command line

spquery.js takes a ShapePath (,-separated for a union), a schema, -d data and -m shape map:

./bin/spquery.js \
  '@<http://project.example/schema#DiscItem>~<http://project.example/ns#href>,@<http://project.example/schema#Issue>~<http://project.example/ns#spec>/valueExpr/shapeExprs~<http://project.example/ns#href>' \
  node_modules/shape-path-core/examples/issue/Issue.json \
  -d node_modules/shape-path-core/examples/issue/Issue2.ttl \
  -m '<http://instance.example/project1/Issue2>@<http://project.example/schema#Issue>'

[
  "http://instance.example/project1/img1.jpg",
  "http://instance.example/project1/spec3"
]

(or npm run toy from this directory).

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