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ShEx: Shape Expression language for Ruby

This is a pure-Ruby library for working with the Shape Expressions Language to validate the shape of RDF graphs.

Gem Version Build Status Coverage Status Gitter chat DOI

Features

  • 100% pure Ruby with minimal dependencies and no bloat.
  • Fully compatible with ShEx specifications.
  • 100% free and unencumbered public domain software.

Description

The ShEx gem implements a ShEx Shape Expression engine version 2.0.

  • ShEx::Parser parses ShExC and ShExJ formatted documents generating executable operators which can be serialized as [S-Expressions][].
  • ShEx::Algebra executes operators against Any RDF::Graph, including compliant RDF.rb.
  • Implementation Report

Examples

Validating a node using ShExC

require 'rdf/turtle'
require 'shex'

shexc = %(
  PREFIX doap:  <http://usefulinc.com/ns/doap#>
  PREFIX dc:    <http://purl.org/dc/terms/>
  PREFIX ex:    <http://example.com/>

  ex:TestShape EXTRA a {
    a [doap:Project];
    ( doap:name Literal;
      doap:description Literal
    | dc:title Literal;
      dc:description Literal)+;
    doap:category    IRI*;
    doap:developer   IRI+;
    doap:implements [<http://shex.io/shex-semantics/>]
  }
)
graph = RDF::Graph.load("etc/doap.ttl")
schema = ShEx.parse(shexc)
map = {
  RDF::URI("https://rubygems.org/gems/shex") => RDF::URI("http://example.com/TestShape")
}
schema.satisfies?(graph, map)
# => true

Validating a node using ShExJ

require 'rubygems'
require 'rdf/turtle'
require 'shex'

shexj = %({
  "@context": "http://www.w3.org/ns/shex.jsonld",
  "type": "Schema",
  "shapes": [{
    "id": "http://example.com/TestShape",
    "type": "Shape",
    "extra": ["http://www.w3.org/1999/02/22-rdf-syntax-ns#type"],
    "expression": {
      "type": "EachOf",
      "expressions": [{
        "type": "TripleConstraint",
        "predicate": "http://www.w3.org/1999/02/22-rdf-syntax-ns#type",
        "valueExpr": {
          "type": "NodeConstraint",
          "values": ["http://usefulinc.com/ns/doap#Project"]
        }
      }, {
        "type": "OneOf",
        "expressions": [{
            "type": "EachOf",
            "expressions": [{
              "type": "TripleConstraint",
              "predicate": "http://usefulinc.com/ns/doap#name",
              "valueExpr": {
                "type": "NodeConstraint",
                "nodeKind": "literal"
              }
            }, {
              "type": "TripleConstraint",
              "predicate": "http://usefulinc.com/ns/doap#description",
              "valueExpr": {
                "type": "NodeConstraint",
                "nodeKind": "literal"
              }
            }]
          }, {
            "type": "EachOf",
            "expressions": [{
              "type": "TripleConstraint",
              "predicate": "http://purl.org/dc/terms/title",
              "valueExpr": {
                "type": "NodeConstraint",
                "nodeKind": "literal"
              }
            }, {
              "type": "TripleConstraint",
              "predicate": "http://purl.org/dc/terms/description",
              "valueExpr": {
                "type": "NodeConstraint",
                "nodeKind": "literal"
              }
            }]
          }],
          "min": 1,
          "max": -1
        }, {
          "type": "TripleConstraint",
          "predicate": "http://usefulinc.com/ns/doap#category",
          "valueExpr": {
            "type": "NodeConstraint",
            "nodeKind": "iri"
          },
          "min": 0,
          "max": -1
        }, {
          "type": "TripleConstraint",
          "predicate": "http://usefulinc.com/ns/doap#developer",
          "valueExpr": {
            "type": "NodeConstraint",
            "nodeKind": "iri"
          },
          "min": 1,
          "max": -1
        }, {
          "type": "TripleConstraint",
          "predicate": "http://usefulinc.com/ns/doap#implements",
          "valueExpr": {
            "type": "NodeConstraint",
            "values": [
              "http://shex.io/shex-semantics/"
            ]
          }
        }
      ]
    }
  }
]})
graph = RDF::Graph.load("etc/doap.ttl")
schema = ShEx.parse(shexj, format: :shexj)
map = {
  RDF::URI("https://rubygems.org/gems/shex") => RDF::URI("http://example.com/TestShape")
}
schema.satisfies?(graph, map)
# => true

Extensions

ShEx has an extension mechanism using Semantic Actions. Extensions may be implemented in Ruby ShEx by sub-classing {ShEx::Extension} and implementing {ShEx::Extension#visit} and possibly {ShEx::Extension#initialize}, {ShEx::Extension#enter}, {ShEx::Extension#exit}, and {ShEx::Extension#close}. The #visit method will be called as part of the #satisfies? operation.

require 'shex'
class ShEx::Test < ShEx::Extension("http://shex.io/extensions/Test/")
  # (see ShEx::Extension#initialize)
  def initialize(schema: nil, logger: nil, depth: 0, **options)
    ...
  end

  # (see ShEx::Extension#visit)
  def visit(code: nil, matched: nil, expression: nil, depth: 0, **options)
    ...
  end
end

The #enter method will be called on any {ShEx::Algebra::TripleExpression} that includes a {ShEx::Algebra::SemAct} referencing the extension, while the #exit method will be called on exit, even if not satisfied.

The #initialize method is called when {ShEx::Algebra::Schema#execute} starts and #close called on exit, even if not satisfied.

To make sure your extension is found, make sure to require it before the shape is executed.

Command Line

When the linkeddata gem is installed, RDF.rb includes a rdf executable which acts as a wrapper to perform a number of different operations on RDF files, including ShEx. The commands specific to ShEx is

  • shex: Validate repository given shape

Using this command requires either a shex-input where the ShEx schema is URI encoded, or shex, which references a URI or file path to the schema. Other required options are shape and focus.

Example usage:

rdf shex https://raw.githubusercontent.com/ruby-rdf/shex/develop/etc/doap.ttl \
  --schema https://raw.githubusercontent.com/ruby-rdf/shex/develop/etc/doap.shex \
  --focus https://rubygems.org/gems/shex

Documentation

https://ruby-rdf.github.io/shex

Implementation Notes

The ShExC parser uses the EBNF gem to generate a PEG parser.

The parser uses the executable [S-Expressions][] generated from the EBNF ShExC grammar to create a set of executable {ShEx::Algebra} Operators which are directly executed to perform shape validation.

Dependencies

Installation

The recommended installation method is via RubyGems. To install the latest official release of RDF.rb, do:

% [sudo] gem install shex

Download

To get a local working copy of the development repository, do:

% git clone git://github.com/ruby-rdf/shex.git

Alternatively, download the latest development version as a tarball as follows:

% wget https://github.com/ruby-rdf/shex/tarball/master

Resources

Mailing List

Author

Contributing

This repository uses Git Flow to mange development and release activity. All submissions must be on a feature branch based on the develop branch to ease staging and integration.

  • Do your best to adhere to the existing coding conventions and idioms.
  • Don't use hard tabs, and don't leave trailing whitespace on any line. Before committing, run git diff --check to make sure of this.
  • Do document every method you add using YARD annotations. Read the tutorial or just look at the existing code for examples.
  • Don't touch the .gemspec or VERSION files. If you need to change them, do so on your private branch only.
  • Do feel free to add yourself to the CREDITS file and the corresponding list in the the README. Alphabetical order applies.
  • Don't touch the AUTHORS file. If your contributions are significant enough, be assured we will eventually add you in there.
  • Do note that in order for us to merge any non-trivial changes (as a rule of thumb, additions larger than about 15 lines of code), we need an explicit public domain dedication on record from you, which you will be asked to agree to on the first commit to a repo within the organization. Note that the agreement applies to all repos in the Ruby RDF organization.

License

This is free and unencumbered public domain software. For more information, see https://unlicense.org/ or the accompanying {file:LICENSE} file.