Generate RDFS vocabulary files from YAML

This script in this module converts a simple RDF vocabulary, described in YAML, into a formal RDFS in JSON-LD, Turtle, and HTML+RDFa. Optionally, a simple JSON-LD @context is also generated for the vocabulary. Neither the script nor the YAML format is prepared for complex vocabularies; its primary goal is to simplify the generation of simple, straightforward RDFS vocabularies not requiring, for instance, sophisticated OWL statements.

When running, the script relies on two files:

1. The vocabulary.yml file, containing the definition for the vocabulary entries. (It is also possible to use a different name for the YAML file, see below.)
2. The template.html file, used to create the HTML file version of the vocabulary. (It is also possible to use a different name for the template file, see below.)

Definition of the vocabulary in the YAML file

The vocabulary is defined in a YAML file, which contains several block sequences with the following keys: vocab, prefix, ontology, class, property, individual, and datatype. Only the vocab and ontology blocks are required, all others are optional.

Each block sequence consists of blocks with the following keys:id, property, value, label, upper_value, domain, range, deprecated, comment, status, defined_by, context, and see_also. The interpretation of these key/value pairs may depend on the top level block where they reside, but some have a common interpretation.

• Common key/value pairs for the class, property, datatype, and individual blocks:

  • label refers to a short header label to the term. If missing, the capitalized value of id is used.
  • comment refers to a longer description of the term, and can be used for blocks in the class, property and individual top-level blocks. It may include HTML Flow content elements. The comment will be encapsulated into an HTML <div> element and will then be displayed verbatim in the HTML version of the vocabulary, and as a literal of type rdf:HTML in the JSON-LD and Turtle versions. Note that the Markdown syntax for simple formatting, like the use of backtick for <code.../>, may also be used.
  • type refers to RDF types. Note that the tool automatically adds types like rdf:Property, rdfs:Class, etc.; this key is to be used for the vocabulary specific types only.
  • defined_by should be a URL, or a list thereof, referring to the formal definition(s) of the term.
  • see_also refers to one or more blocks with label and url keys, providing a human readable title and a URL, respectively, to an external document that can be referred to by the description of the term. (These are translated into an rdfs:seeAlso term in the vocabulary.)
  • The status key refers to a string that can be stable, reserved, or deprecated. The terms are divided, in the HTML output, into these three sections. stable is the default.
  • The deprecated key refers to a boolean, signaling whether term is deprecated or not. Default is false. This property is a leftover from earlier version and is overwritten, if applicable, by the value of status.
  • The context key refers to list of URLs or two special keywords. It is used to add information on JSON-LD @context file(s) that "mention" the term; the list of URLs refer to the relevant @context file. If the value is vocab, and a global @context file is defined in the vocab block, that "default" @context is used. Finally, if the value of the property is none, there is no context file reference for the term. The default setting is vocab (i.e., unless it is otherwise specified, the default value is used for the term).
  • The example key refers to on or more blocks with label and json keys, providing a (JSON) example with a title. These examples are placed, in the HTML version, to the end of the section referring to a term (the examples are ignored in the Turtle and the JSON-LD versions). Care should be taken to use the "|" block style indicator in the YAML file for the examples.

  For these blocks the id key, and either the comment or the defined_by keys, are required. All the others are optional.

• Top level blocks:

  • vocab: a block with the id and the value keys defining the prefix and the URL of the vocabulary, respectively. The id provides a prefix that can be used in the vocabulary descriptions, e.g., for cross references. The additional, optional context key may provide a default context file reference (as a URI), used by all terms unless locally overwritten (see above).

  • prefix: definition of a prefixes, and corresponding URLs, for each external external vocabulary in use, defined by the id and value keys, respectively.

    Some id/value pairs are defined by default, and it is not necessary to define them here. These are: dc (for http://purl.org/dc/terms/), owl (for http://www.w3.org/2002/07/owl#), rdf (for http://www.w3.org/1999/02/22-rdf-syntax-ns#), rdfs (for http://www.w3.org/2000/01/rdf-schema#), xsd (for http://www.w3.org/2001/XMLSchema#), and schema (for http://schema.org/).

  • ontology: definition of "ontology properties", that is, statements made about the vocabulary itself. The (prefixed) property term is defined by the property key, and the value by the value key. If the value can be parsed as a URL, it is considered to be the URL of an external resource; otherwise, the value is considered to be (English) text.

    It is good practice to provide, at least, dc:description as an ontology property with a short description of the vocabulary.

    The script automatically adds a dc:date key with the generation time as a value.

  • class: blocks of a class definitions. For each class he id key defines the class name (no prefix should be used here). Possible superclasses are defined by the upper_value key as a single term, or a sequence of terms.

  • property: blocks of a property definitions. For each property the id key defines the property name (no prefix should be used here); possible superproperties are defined in the by the upper_value as a single term, or as a sequence of terms. The domain and range classes can also be provided as a single term, or as a sequence of terms, through the domain and range keys, respectively.

    Note that both the domain and the range keys can take an array of class references as values. For the former this means the resulting domain is the union of the referred classes, whereas for the latter it is the intersection.

    The range key may also use the (single) IRI (or URL) term instead of class references. This keyword denotes a property that has no explicit range, but whose objects are expected to be IRI references. The generated vocabulary annotates these properties as belonging to the owl:ObjectProperty class, which is the term reserved for properties whose objects are not supposed to be literals.

    The dataset key can also be set to a boolean value. This key only influences the generated JSON-LD @context: if the value is true, the JSON-LD @container is set to the @graph value for the property, signalling that the value refers to a dataset (or graph). See the JSON-LD Specification for further details.

  • individual: blocks of definitions of individuals, i.e., a single resources defined in the vocabulary. For each individual the id key defines the property name (no prefix should be used here); the possible types are defined in the block for type as a single term, or a sequence of terms. (Earlier versions of this tool used upper_value for the same purpose, but that usage, though still understood for backward compatibility reasons, is deprecated.)

  • datatype: blocks of datatype definitions. For each datatype the id key defines the datatype name (no prefix should be used here). The possible types are defined in the block for upper_value or for type, as a single term for possible datatype this is derived from.

There are some examples in the example directory on github that illustrate all of these terms.

Installation and use

The script is in TypeScript (version 5.0.2 and beyond) running on top of node.js (version 16 and beyond).

Beyond the YAML file itself, the script relies on an HTML template file, i.e., a skeleton file in HTML that is completed by the vocabulary entries. The example template file on github provides a good starting point for a template that also makes use of respec. The script relies on the existing id values and section structures to be modified/extended by the script. Unused subsections (e.g., when there are no deprecated classes) are removed from the final HTML file.

Installation from npm

The script can be used as a standard npm module via:

npm install yml2vocab

Running on a command line

The npm installation installs the node_modules/.bin/yml2vocab script. The script can be used as:

yml2vocab [-v vocab_file_name] [-t template_file_name] [-c]

Running this script generates the vocab_file_name.ttl, vocab_file_name.jsonld, and vocab_file_name.html files for the Turtle, JSON-LD, and HTML+RDFa versions, respectively. The script relies on the vocab_file_name.yml file for the vocabulary specification in YAML and a template_file_name file for a template file. The defaults are vocabulary and template.html, respectively.

If the -c flag is also set, the additional vocab_file_name_context.jsonld is also generated, containing a simple @context structure that can be used as a separate @context file or embedded in a JSON file. Note that this is a "minimal" JSON-LD file, which does not necessarily use all the sophistication that JSON-LD defines for @context; these may have to be added manually.

Running from a Javascript/TypeScript program

The simplest way of using the module from Javascript is:

const yml2vocab = require('yml2vocab');
async function main() {
    await yml2vocab.generateVocabularyFiles("vocabulary","template.html",false);
}
main();

This reads (asynchronously) the YAML and template files and stores the generated vocabulary representations (see the command line interface for details) in the directory alongside the YAML file. By setting the last argument to true a @context is also generated.

The somewhat lower level yml2vocab.VocabGeneration class can also be used:

const yml2vocab = require('yml2vocab');
const vocabGeneration = new yml2vocab.VocabGeneration(yml_content);     // YAML content is text form, before parsing
const turtle: string  = vocabGeneration.getTurtle();                    // returns the turtle content as a string
const jsonld: string  = vocabGeneration.getJSONLD();                    // returns the JSON-LD content as a string
const html: string    = vocabGeneration.getHTML(template_file_content); // returns the HTML+RDFa content as a string
const html: string    = vocabGeneration.getContext();                   // returns the minimal @context file for the vocabulary

If TypeScript is used instead of Javascript the same works, except that the require must be replaced by:

import yml2vocab from 'yml2vocab';

There is no need to install any extra typing, it is included in the package. The interfaces are simply using strings, no extra TypeScript type definitions have been defined.

Cloning the repository

The repository may also be cloned. For a complete installation:

1. If necessary, install node.js on your local machine. Installation of node.js should automatically install the npm package manager.

2. Clone the repository (i.e., https://github.com/w3c/yml2vocab/) to your local machine.

3. In the directory of the repository clone, run npm install on the command line. This installs all the necessary packages in the node_modules subdirectory.

4. Create a directory for the vocabulary definition; this should include

   1. A vocabulary.yml file. You can start with the YAML file in the example directory of the repository, and change the cells for your vocabulary.
   2. A template.html file. You can start with the HTML file in the example directory of the repository, and adapt/change it as you wish.

5. Run the main.ts file in the directory vocabulary definition. This generates the vocabulary.ttl, vocabulary.jsonld, and vocabulary.html files for, respectively, the Turtle, JSON-LD, and HTML representations.

   "Running" may be done in two different ways:

   1. Run, via node, the file dist/main.js of the repository
   2. Run, via node_modules/.bin/ts-node, the file main.ts of the repository

   The script also accepts a single argument to be used instead of vocabulary to name the various files (see above).

Content of the directory

• Readme.md: this file.
• package.json: configuration file for npm.
• example: a folder with examples for vocabulary definition files and the generated RDF vocabulary files.
• lib directory: the TypeScript modules for the script.
• dist directory: the Javascript distribution files (compiled from the TypeScript sources)
• main.ts: the TypeScript entry point to the script as a command line tool
• index.ts: the top level type interface, to be used if the files are used by an external script.

The following files and directories are generated/modified by either the script or npm; better not to touch these directly:

• package-lock.json: used by npm as an internal file for the packages.
• node_modules directory: the various Javascript libraries used by the script. This directory should not be uploaded to github, it is strictly for the local activation of the script.

Acknowledgement

The original idea, structure, and script (in Ruby) was created by Gregg Kellogg for v1 of the Credentials Vocabulary and with a vocabulary definition using CSV. The CSV definitions have been changed to YAML, and the script itself has been re-written in TypeScript (and developed further since).