A Jekyll plugin for including RDF data in your static site
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README.md

jekyll-rdf

A Jekyll plugin for including RDF data in your static site.

Gem Version Build Status Coverage Status

The API Documentation is available at RubyDoc.info.

Contents

  1. Installation
  2. Usage
    1. Configuration
    2. Building the Jekyll Site
    3. Defining Templates
  3. Parameters and configuration options at a glance
    1. Resource Attributes
    2. Liquid Filters
    3. Plugin Configuration (_config.yml)
  4. Development
  5. License

Installation

As a prerequisite for Jekyll RDF you of course need to install Jekyll. Please take a look at the installations instructions at https://jekyllrb.com/docs/installation/.

If you already have a working Jekyll installation you can add the the Jekyll-RDF plugin. Probably you already using Bundler and there is a Gemfile in your Jekyll directory. Add Jekyll-RDF to the plugins section:

group :jekyll_plugins do
    gem "jekyll-rdf", '~> 3.0.0.pre.a'
    …
end

Replace the version string with the currently available stable release as listed on rubygems.org. After updating your Gemfile you probably want to run bundle install (or bundle install --path vendor/bundle) or bundle update.

If you are not using a Gemfile to manage your jekyll/ruby packages install Jekyll-RDF using gem:

gem install jekyll-rdf

If you want to build the plugin from source, please have a look at our Development section.

Usage

This section explains how to use Jekyll-RDF in three steps:

  1. Configuration
  2. Building the Jekyll Site
  3. Defining Templates

All filters and methods to use in templates and configuration options are documented in the section “Parameters and configuration options at a glance”.

Configuration

First, you need a jekyll page. In order to create one, just do:

jekyll new my_page
cd my_page

Further there are some parameters required in your _config.yml for jekyll-rdf. I.e. the url and baseurl parameters are used for including the resource pages into the root of the site, the plug-in has to be configured, and the path to the RDF file has to be present.

baseurl: "/simpsons"
url: "http://example.org"

plugins:
    - jekyll-rdf

jekyll_rdf:
    path: "_data/data.ttl"
    default_template: "default.html"
    restriction: "SELECT ?s WHERE { ?s ?p ?o . FILTER regex(str(?s), "http://example.org/simpsons")  }"
    class_template_mappings:
        "http://xmlns.com/foaf/0.1/Person": "person.html"
    instance_template_mappings:
        "http://example.org/simpsons/Abraham": "abraham.html"

Map resources to templates

It is possible to map a specific class (resp. RDF-type) or individual resources to a template.

  class_template_mappings:
      "http://xmlns.com/foaf/0.1/Person": "person.html"
  instance_template_mappings:
      "http://aksw.org/Team": "team.html"

A template mapped to a class will be used to render each instance of that class and its subclasses. Each instance is rendered with its most specific class mapped to a template. If the mapping is ambiguous for a resource, a warning will be output to your command window, so watch out!

It is also possible to define a default template, which is used for all resources, which are not covered by the class_template_mappings or instance_template_mappings.

  default_template: "default.html"

Restrict resource selection

Additionally, you can restrict the overall resource selection by adding a SPARQL query as restriction parameter to _config.yml. Please use ?resourceUri as the placeholder for the resulting literal:

  restriction: "SELECT ?resourceUri WHERE { ?resourceUri <http://www.ifi.uio.no/INF3580/family#hasFather> <http://www.ifi.uio.no/INF3580/simpsons#Homer> }"

There are 3 pre-defined keywords for restrictions implemented:

  • subjects will load all subject URIs
  • predicates will load all predicate URIs
  • objects will load all object URIs

Blank Nodes

Furthermore you can decide if you want to render blank nodes or not. You just need to add include_blankto _config.yml:

jekyll_rdf:
  include_blank: true

Preferred Language

Finally it is also possible to set a preferred language for the RDF-literals with the option language:

jekyll_rdf:
  language: "en"

Building the Jekyll Site

Running jekyll build will render the RDF resources to the _site/… directory. Running jekyll serve will render the RDF resources and provide you with an instant HTTP-Server usually accessible at http://localhost:4000/. RDF resources whose IRIs don't start with the configured jekyll url and baseurl are rendered to the _site/rdfsites/… subdirectory.

Defining Templates

To make use of the RDF data, create one or more files (e.g rdf_index.html or person.html) in the _layouts-directory. For each resource a page will be rendered. See example below:

---
layout: default
---
<div class="home">
  <h1 class="page-heading"><b>{{ page.rdf.iri }}</b></h1>
  <p>
    <h3>Statements in which {{ page.rdf.iri }} occurs as subject:</h3>
    {% include statements_table.html collection=page.rdf.statements_as_subject %}
  </p>
  <p>
    <h3>Statements in which {{ page.rdf.iri }} occurs as predicate:</h3>
    {% include statements_table.html collection=page.rdf.statements_as_predicate %}
  </p>
  <p>
    <h3>Statements in which {{ page.rdf.iri }} occurs as object:</h3>
    {% include statements_table.html collection=page.rdf.statements_as_object %}
  </p>
</div>

Template Examples

We included some template examples at

  • test/source/_layouts/rdf_index.html
  • test/source/_layouts/person.html

Get the IRI of a resource

{{ page.rdf }}

Is the currently rendered resource.

{{ page.rdf.iri }}

Returns the IRI of the currently rendered resource.

To access objects which are connected to the current subject via a predicate you can use our custom liquid filters. For single objects or lists of objects use the rdf_property-filter (see 1 and 2).

Single Objects

To access one object which is connected to the current subject through a given predicate please filter page.rdf data with the rdf_property-filter. Example:

Age: {{ page.rdf | rdf_property: '<http://xmlns.com/foaf/0.1/age>' }}

Optional Language Selection

To select a specific language please add a a second parameter to the filter:

Age: {{ page.rdf | rdf_property: '<http://xmlns.com/foaf/0.1/job>','en' }}

Multiple Objects

To get more than one object connected to the current subject through a given predicate please use the filter rdf_property in conjunction with a third argument set to true (the second argument for the language can be omitted by setting it to nil):

Sisters: <br />
{% assign resultset = page.rdf | rdf_property: '<http://www.ifi.uio.no/INF3580/family#hasSister>', nil, true %}
<ul>
{% for result in resultset %}
    <li>{{ result }}</li>
{% endfor %}
</ul>

Optional Language Selection

To select a specific language please add a second parameter to the filter:

Book titles: <br />
{% assign resultset = page.rdf | rdf_property: '<http://xmlns.com/foaf/0.1/currentProject>','de' %}
<ul>
{% for result in resultset %}
    <li>{{ result }}</li>
{% endfor %}
</ul>

RDF Containers and Collections

To support RDF Containers and RDF Collections we provide the rdf_container and rdf_collection filters.

In both cases the respective container resource resp. head of the collection needs to be identified and then passed through the respective filter. For containers we currently support explicit instances of rdf:Bag, rdf:Seq and rdf:Alt with the members identified using the rdfs:ContainerMembershipPropertys: rdf:_1, rdf:_2, rdf:_3 …. Collections are identified using rdf:first, rdf:rest and terminated with L rdf:rest rdf:nil. Since the head of a collection needs to be identified you cannot use a blank node there, you can identify it indirectly through the predicate which contains the collection.

Example graph:

@prefix ex: <http://example.org/> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

ex:Resource ex:lists ex:List ;
            ex:directList ("hello" "from" "turtle") .
            ex:hasContainer ex:Container .

ex:List rdf:first "hello" ;
        rdf:rest ("rdf" "list") .

ex:Container a rdf:Bag ;
             rdf:_1 "hello" ;
             rdf:_2 "rdf" ;
             rdf:_3 "container" .

The template for ex:Resource:

{% assign list = page.rdf | rdf_collection: '<http://example.org/directList>' %}
<ol>
{% for item in list %}
<li>{{ item }}</li>
{% endfor %}
</ol>

{% assign container = page.rdf | rdf_property: '<http://example.org/hasContainer>' | rdf_container %}
<ul>
{% for item in container %}
<li>{{ item }}</li>
{% endfor %}
</ul>

Custom SPARQL Query

We implemented a liquid filter sparql_query to run custom SPARQL queries. Each occurence of ?resourceUri gets replaced with the current URI. Caution: You have to separate query and resultset variables because of Liquids concepts. Example:

{% assign query = 'SELECT ?sub ?pre WHERE { ?sub ?pre ?resourceUri }' %}
{% assign resultset = page.rdf | sparql_query: query %}
<table>
{% for result in resultset %}
  <tr>
    <td>{{ result.sub }}</td>
    <td>{{ result.pre }}</td>
  </tr>
{% endfor %}
</table>

Defining Prefixes for RDF

It is possible to declare a set of prefixes which can be used in the rdf_property and sparql_query liquid-filters. This allows to shorten the amount of text required for each liquid-filter. The syntax of the prefix declarations the same as for SPARQL 1.1. Just put your prefixes in a separate file and include the key rdf_prefix_path together with a relative path in the YAML Front Matter of a file where your prefixes should be used.

For the prefixes the same rules apply as for other variables defined in the YAML Front Matter. “These variables will then be available to you to access using Liquid tags both further down in the file and also in any layouts or includes that the page or post in question relies on.” (source: YAML Front Matter). This is especially relevant if you are using prefixes in includes.

Dealing with Fragment Identifiers

If the URI of a resource contains a fragment identifier (#…) the resource can be hosted together with other resources with the same base URI up to the fragment identifier on a single page. The page will by accessible through the base URI, while in the template the individual URIs with a fragment identifier are accessible through the collection page.sub_rdf.

Example

In the _config.yml:

  'instance_template_mappings' :
    'http://www.ifi.uio.no/INF3580/simpsons' : 'family.html'

In _layouts/family.html:

  {% for member in page.sub_rdf%}
    {% include simPerson.html person = member%}
  {% endfor %}

The example uses the template family.html to render a single page containing every resource whose URI begins with http://www.ifi.uio.no/INF3580/simpsons#, was well as the resource http://www.ifi.uio.no/INF3580/simpsons itself. Jekyll-rdf collects all resources with a fragment identifier in their URI (from here on called subResources) and passes them through page.sub_rdf into the templates of its superResource (resources whose base URI is the same as of its subResources except for the fragment identifier).

Parameters and configuration options at a glance

Resource Attributes

Every resource returned by one of jekyll-rdfs filters is an object that liquid can also handle like a string. They all have the following methods usable in Liquid.

Resource.statements_as_subject

Return a list of statements whose subject is the current resource. The statements in the returned list can be accessed by addressing their positions: Statement.subject, Statement.predicate, respective Statement.object.

Resource.statements_as_predicate

Return a list of statements whose predicate is the current resource. The statements in the returned list can be accessed by addressing their positions: Statement.subject, Statement.predicate, respective Statement.object.

Resource.statements_as_object

Return a list of statements whose object is the current resource. The statements in the returned list can be accessed by addressing their positions: Statement.subject, Statement.predicate, respective Statement.object.

Resource.page_url

Return the URL of the page representing this RdfResource.

Resource.render_path

Return the path to the page representing this RdfResource. Use it with care.

Resource.covered

This method is relevant for rendering pages for IRIs containing a fragment identifier (http://superresource#anchor). This method returns true for the super-resource (http://superresource) if it is actually described in the given knowledgebase.

Resource.inspect

Returns a verbose String representing this resource.

Liquid Filters

rdf_get

Synopsis: <resource_iri> | rdf_get

Parameters:

  • <resource_iri> is a string representing an RDF resource, with prefix (prefix:name) or a full IRI (<http://ex.org/name>). To reference the resource of the current page use page.rdf, page, or nil.

Description: Takes the provided IRI and returns the corresponding RdfResource object from your knowledge base. On this object you can call the methods as described in the section Resource.

Example:

{{'<http://www.ifi.uio.no/INF3580/simpsons>' | rdf_get }}

Result:

http://www.ifi.uio.no/INF3580/simpsons

rdf_property

Synopsis: <rdf_resource> OR <rdf_resource_string> | rdf_property: <property>, [<lang>] OR [<lang>, <list>] OR [nil, <list>]

Parameters:

  • <rdf_resource> is an RdfResource. To reference the resource of the current page use page.rdf, page, or nil.
  • <rdf_resource_string> is a String representing the IRI of <rdf_resource>.
  • <property> is a string representing an RDF predicate, with prefix (prefix:name) or a full IRI (<http://ex.org/name>).
  • <lang> is a language tag (e.g. de). If this parameter is omitted replace it by nil.
  • <list> is a boolean value (true, false).

Description: Returns the object, of the triple <rdf_resource> <predicate> ?object. The returned object can by any of the kind, resource, literal, or blanknode.

Example (default):

{assign resource = '<http://www.ifi.uio.no/INF3580/simpsons#Homer>' | rdf_get }
{{ resource | rdf_property: '<http://xmlns.com/foaf/0.1/job>' }}

Result:

"unknown"

Example (string):

{{ '<http://www.ifi.uio.no/INF3580/simpsons#Homer>' | rdf_property: '<http://xmlns.com/foaf/0.1/job>' }}

Result:

"unknown"

Example (with language):

{assign resource = '<http://www.ifi.uio.no/INF3580/simpsons#Homer>' | rdf_get }
{{ resource | rdf_property: '<http://xmlns.com/foaf/0.1/job>', 'de' }}

Result:

"unbekannt"

Example (return as list):

{assign resource = '<http://www.ifi.uio.no/INF3580/simpsons#Homer>' | rdf_get }
{% assign resultset = resource | rdf_property: '<http://xmlns.com/foaf/0.1/job>', nil, true %}
{% for result in resultset %}
<li>{{ result }}</li>
{% endfor %}

Result:

<li>"unknown"</li>
<li>"unbekannt"</li>
<li>"unbekannter Job 2"</li>
<li>"unknown Job 2"</li>

rdf_inverse_property

Synopsis: <rdf_resource> OR <rdf_resource_string>| rdf_inverse_property: <property>, [<list>]

Parameters:

  • <rdf_resource> is an RdfResource. To reference the resource of the current page use page.rdf, page, or nil.
  • <rdf_resource_string> is a String representing the IRI of <rdf_resource>.
  • <property> is a string representing an RDF predicate, with prefix (prefix:name) or a full IRI (<http://ex.org/name>).
  • <list> is a boolean value (true, false).

Description: Same as rdf_property, but in inverse direction. It returns the subject, of the triple ?subject <predicate> <rdf_resource>. The returned object can by any of the kind, resource, or blanknode.

Examples (default):

{assign resource = '<http://www.ifi.uio.no/INF3580/simpsons#Homer>' | rdf_get }
{{ page.rdf | rdf_inverse_property: '<http://www.ifi.uio.no/INF3580/family#hasFather>' }}

Result:

http://www.ifi.uio.no/INF3580/simpsons#Bart

Examples (string):

{{ '<http://www.ifi.uio.no/INF3580/simpsons#Homer>' | rdf_inverse_property: '<http://www.ifi.uio.no/INF3580/family#hasFather>' }}

Result:

http://www.ifi.uio.no/INF3580/simpsons#Bart

Example (as list):

{assign resource = '<http://www.ifi.uio.no/INF3580/simpsons#Homer>' | rdf_get }
{% assign resultset = resource | rdf_property: '<http://www.ifi.uio.no/INF3580/family#hasFather>', true %}
{% for result in resultset %}
<li>{{ result }}</li>
{% endfor %}

Result:

http://www.ifi.uio.no/INF3580/simpsons#Bart
http://www.ifi.uio.no/INF3580/simpsons#Lisa
http://www.ifi.uio.no/INF3580/simpsons#Maggie

sparql_query

Synopsis: <rdf_resource> | sparql_query: <query> OR <reference_array> | sparql_query: <query> OR <query> | sparql_query

Parameters:

  • <rdf_resource> is an RdfResource which will replace ?resourceUri in the query. To omit this parameter or reference the resource of the current page use page.rdf, page, or nil.
  • <reference_array> an array containing IRIs as Strings or rdf_resource. They will consecutively replace each ?resourceUri_<index> in your query.
  • <query> a string containing a SPARQL query.

Description: Evaluates query on the given knowledge base and returns an array of results (result set). Each entry object in the result set (result) contains the selected variables as resources or literals. You can use ?resourceUri inside the query to reference the resource which is given as <rdf_resource>.

Example (page)

<!--Rendering the page of resource Lisa -->
{% assign query = 'SELECT ?sub ?pre WHERE { ?sub ?pre ?resourceUri }' %}
{% assign resultset = page | sparql_query: query %}
<table>
{% for result in resultset %}
  <tr><td>{{ result.sub }}</td><td>{{ result.pre }}</td></tr>
{% endfor %}
</table>

Result:

<table>
<tr><td>http://www.ifi.uio.no/INF3580/simpsons#TheSimpsons</td><td>http://www.ifi.uio.no/INF3580/family#hasFamilyMember</td></tr>
<tr><td>http://www.ifi.uio.no/INF3580/simpsons#Bart</td><td>http://www.ifi.uio.no/INF3580/family#hasSister</td></tr>
<tr><td>http://www.ifi.uio.no/INF3580/simpsons#Maggie</td><td>http://www.ifi.uio.no/INF3580/family#hasSister</td></tr>
...

Example (array)

{% assign query = 'SELECT ?x WHERE {?resourceUri_0 ?x ?resourceUri_1}' %}
{% assign array = "<http://www.ifi.uio.no/INF3580/simpsons#Homer>,<http://www.ifi.uio.no/INF3580/simpsons#Marge>" | split: %}
{% assign resultset = array | sparql_query: query %}
<table>
{% for result in resultset %}
  <tr><td>{{ result.x }}</td></tr>
{% endfor %}
</table>

Result:

<table>
  <tr><td>http://www.ifi.uio.no/INF3580/family#hasSpouse</td></tr>
</table>

Example (query)

{% assign query = 'SELECT ?x WHERE {<http://www.ifi.uio.no/INF3580/simpsons#Homer> ?x <http://www.ifi.uio.no/INF3580/simpsons#Marge>}' %}
{% assign resultset = query | sparql_query %}
<table>
{% for result in resultset %}
  <tr><td>{{ result.x }}</td></tr>
{% endfor %}
</table>

Result:

<table>
  <tr><td>http://www.ifi.uio.no/INF3580/family#hasSpouse</td></tr>
</table>

rdf_container

Synopsis: <rdf_container_head> **OR** <rdf_container_head_string> | rdf_container

Parameters:

  • <rdf_container_head> is an RdfResource. To reference the resource of the current page use page.rdf, page, or nil.
  • <rdf_container_head_string> is a String representing the IRI of <rdf_container_head>.

Description: Returns an array with resources for each element in the container whose head is referenced by rdf_container_head.

Examples:

{% assign resource = '<http://www.ifi.uio.no/INF3580/simpson-container#Container>' | rdf_get %}
{% assign array = resource | rdf_container %}
{% for item in array %}
{{ item }}
{% endfor %}
Result:
http://www.ifi.uio.no/INF3580/simpsons#Homer
http://www.ifi.uio.no/INF3580/simpsons#Marge
http://www.ifi.uio.no/INF3580/simpsons#Bart
http://www.ifi.uio.no/INF3580/simpsons#Lisa
http://www.ifi.uio.no/INF3580/simpsons#Maggie

Examples: (string)

{% assign array = '<http://www.ifi.uio.no/INF3580/simpson-container#Container>' | rdf_container %}
{% for item in array %}
{{ item }}
{% endfor %}
Result:
http://www.ifi.uio.no/INF3580/simpsons#Homer
http://www.ifi.uio.no/INF3580/simpsons#Marge
http://www.ifi.uio.no/INF3580/simpsons#Bart
http://www.ifi.uio.no/INF3580/simpsons#Lisa
http://www.ifi.uio.no/INF3580/simpsons#Maggie

rdf_collection

Synopsis: <rdf_collection_head> OR <rdf_collection_head_string> | rdf_collection OR <rdf_resource> | rdf_collection: "<property>"

Parameters:

  • <rdf_collection_head> is an RdfResource. To reference the resource of the current page use page.rdf, page, or nil.
  • <rdf_collection_head_string> is a String representing the IRI of <rdf_collection_head>.
  • <rdf_resource> is an RdfResource. To reference the resource of the current page use page.rdf, page, or nil.
  • <property> is a string representing an RDF predicate, with prefix (prefix:name) or a full IRI (<http://ex.org/name>).

Description: Returns an array with resources for each element in the collection whose head is referenced by rdf_collection_head. Instead of directly referencing a head it is also possible to specify the property referencing the collection head.

Example (specify head resource):

{% assign resource = '<http://www.ifi.uio.no/INF3580/simpson-collection#Collection>' | rdf_get %}
{% assign array = resource | rdf_collection %}
{% for item in array %}
{{ item }}
{% endfor %}

Result:

http://www.ifi.uio.no/INF3580/simpsons#Homer
http://www.ifi.uio.no/INF3580/simpsons#Marge
http://www.ifi.uio.no/INF3580/simpsons#Bart
http://www.ifi.uio.no/INF3580/simpsons#Lisa
http://www.ifi.uio.no/INF3580/simpsons#Maggie

Example (specify head string):

{% assign array = '<http://www.ifi.uio.no/INF3580/simpson-collection#Collection>' | rdf_collection %}
{% for item in array %}
{{ item }}
{% endfor %}

Result:

http://www.ifi.uio.no/INF3580/simpsons#Homer
http://www.ifi.uio.no/INF3580/simpsons#Marge
http://www.ifi.uio.no/INF3580/simpsons#Bart
http://www.ifi.uio.no/INF3580/simpsons#Lisa
http://www.ifi.uio.no/INF3580/simpsons#Maggie

Example (specify via property):

{% assign resource = '<http://www.ifi.uio.no/INF3580/simpsons>' | rdf_get %}
{% assign array = resource | rdf_collection: "<http://www.ifi.uio.no/INF3580/simpsons#familycollection>" %}
{% for item in array %}
{{ item }}
{% endfor %}

Result:

http://www.ifi.uio.no/INF3580/simpsons#Homer
http://www.ifi.uio.no/INF3580/simpsons#Marge
http://www.ifi.uio.no/INF3580/simpsons#Bart
http://www.ifi.uio.no/INF3580/simpsons#Lisa
http://www.ifi.uio.no/INF3580/simpsons#Maggie

Plugin Configuration (_config.yml)

Name Parameter Default Description Example
path Relative path to the RDF-File no default Specifies the path to the RDF file you want to render the website for path: "rdf-data/simpsons.ttl"
language Language-Tag as String no default Specifies the preferred language when you select objects using our Liquid filters language: "en"
include_blank Boolean-Expression false Specifies whether blank nodes should also be rendered or not include_blank: true
restriction SPARQL-Query as String or subjects / objects / predicates no default Restricts the resource-selection with a given SPARQL-Query or the three keywords subjects (only subject URIs), objects, predicates restriction: "SELECT ?resourceUri WHERE { ?resourceUri <http://www.ifi.uio.no/INF3580/family#hasFather> <http://www.ifi.uio.no/INF3580/simpsons#Homer> }"
default_template Filename of the default RDF-template in _layouts directory no default Specifies the template-file you want Jekyll to use to render all RDF resources default_template: "rdf_index.html"
instance_template_mappings Target URI as String : filename of the template as String no default Maps given URIs to template-files for rendering an individual instance instance_template_mappings: "http://www.ifi.uio.no/INF3580/simpsons#Abraham": "abraham.html"
class_template_mappings Target URI as String : filename of the template as String no default Maps given URIs to template-files for rendering all instances of that class class_template_mappings: "http://xmlns.com/foaf/0.1/Person": "person.html"

Development

Installation from source

To install the project with the git-repository you will need git on your system. The first step is just cloning the repository:

git clone git@github.com:white-gecko/jekyll-rdf.git

A folder named jekyll-rdf will be automatically generated. You need to switch into this folder and compile the ruby gem to finish the installation:

cd jekyll-rdf
gem build jekyll-rdf.gemspec
gem install jekyll-rdf -*.gem

Run tests

bundle exec rake test

Test page

Everytime the tests are executed, the Jekyll page inside of test/source gets processed. Start a slim web server to watch the results in web browser, e.g. Pythons SimpleHTTPServer (Python 2, for Python 3 it's http.server):

cd test/source/_site
python -m SimpleHTTPServer 8000

Build API Doc

To generate the API Doc please navigate to jekyll-rdf/lib directory and run

gem install yard
yardoc *

The generated documentation is placed into jekyll-rdf/lib/doc directory.

License

jekyll-rdf is licensed under the MIT license.