Ruby and the Semantic Web

This evening, I gave a talk on using Ruby RDF.rb and assorted gems at the Lotico San Francisco Semantic Meetup. I’ve uploaded slides to Slide Share.

I also showed a simple demo using the GitHub API to create FOAF and DOAP records for accounts and repositories, and to do some simple navigation. The demo is running at http://greggkellogg.net/github-lod, and source is (of course) available on GitHub.

The demo is not intended to be a complete application, but it shows some basic capabilities [Ruby LinkedData][(http://rubygems.org/gems/linkeddata) for generating RDF in a variety of formats from Active Record models (which cache the GitHub API calls). The Web-pages are, of course, marked up with RDFa, and you can use content-negotiation, or append an appropriate extension to the URLs, to retrieve the data in alternative RDF formats.

SPARQL Algebra

For those intrepid enough, I've pushed version 0.0.2 of sparql-algebra. It relies on unreleased changes to RDF.rb and sxp-ruby, so you need to use bundler with the included Gemfile.

SPARQL Algebra implements the s-expression-based SPARQL algebra described in SPARQL 1.1 and Jena. Remaining work needed for _describe_ operator and query optimizations. This is the base for translation from SPARQL Grammar [4], which requires just a bit more work to be fully compliant. Both of these, along with support for an HTTP endpoint and solution serializer, will be sufficient to implement a complete SPARQL solution in pure Ruby.

SPARQL Algebra passes all but four W3C DAWG tests (data-r2), with those four not being worth implementing, in my opinion. As an example of an SSE based on the SPARQL grammar, consider the following:

PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>

SELECT ?mbox ?name
 {
   ?x foaf:mbox ?mbox .
   OPTIONAL { ?x foaf:name  ?name } .
 }

which is equivalent to the following SSE:

(prefix ((foaf: <http://xmlns.com/foaf/0.1/>))
   (project (?mbox ?name)
     (leftjoin
       (bgp (triple ?x foaf:mbox ?mbox))
       (bgp (triple ?x foaf:name ?name)))))

There are outstanding pull requests to RDF.rb and sxp-ruby that are required to release it to RubyGems, but you're encouraged to play with it and send feedback!

Thanks to Arto and Ben for the initial work they did on this, and other enabling projects, as well as creating an excellent executable test suite!

RdfContext version 0.5.4 with provisional RDFa 1.1 support

I just released version 0.5.4 of RdfContext to GitHub and GemCutter. This version is notable for including support for RDFa 1.1 parsing. This is still based on an Working Draft, so it will likely change in the future.

RDFa 1.1 includes support for profiles, vocabularies and terms. And supports using URIs or CURIEs or terms anywhere that's legal within an HTML document. Right now, only the XHTML+RDFa profile is supported.

<div vocab="http://xmlns.com/foaf/0.1/">
   <p about="#me" typeof="Person" property="name">Gregg Kellogg</p>
</div>

<#me> a foaf:Person;
  foaf:name "Gregg Kellogg" .

@prefix rdfa: <http://www.w3.org/ns/rdfa#> .
[ rdfa:prefix "foaf"; rdfa:uri "http://xmlns.com/foaf/0.1/"] .
[ rdfa:prefix "dc"; rdfa:uri "http://purl.org/dc/terms/"] .
[ rda:term "name"; rdfa:uri "http://xmlns.com/foaf/0.1/name"] .
[ rda:term "created"; rdfa:uri "http://purl.org/dc/terms/created"] .

<div profile="http://example.com/my_vocab">
  <p about="#me">
    <span property="name">Gregg Kellogg</span>
    is the author of
    <a rel="created"
        resource="http://github.com/gkellogg/rdf_context">
      RdfContext
    </a>
  </p>
</div>

<div prefix="foaf: http://xmlns.com/foaf/0.1/ dc: http://purl.org/dc/terms/">
  <p about="#me">
    <span property="foaf:name">Gregg Kellogg</span>
    is the author of
    <a rel="dc:created"
        resource="http://github.com/gkellogg/rdf_context">
      RdfContext
    </a>
  </p>
</div>

<div>
    <p about="#me">
      <span property="http://xmlns.com/foaf/0.1/name">
        Gregg Kellogg
      </span>
      is the author of
      <a rel="http://purl.org/dc/terms/created"
          resource="http://github.com/gkellogg/rdf_context">
        RdfContext
      </a>
    </p>
  </div>
  

RdfContext version 0.5.1 brings Turtle and enhanced RDF/XML serializers

 Just pushed version 0.5.1 of RdfContext to GitHub and Gemcutter. This version includes a Serializer framework, including a AbstractSerializer, RecursiveSerializer and Turtle and RDF/XML serializers based on these. The RDF/XML serializer is a big improvement over the previous version, including Typed element names an RDF Container folding using parseType="collection".

RdfContext includes native Ruby parsers for RDF/XML, RDFa and N3-rdf, which includes Turtle and N-Triples. All parsers pass W3C tests (included in specs). It also includes context-aware quad store, with in-memory and SQLite3 storage models.

RdfContext gem released

I've released version 0.4.4 of the RdfContext gem. As the name implies, RdfContext supports contextual data-stores bound to graphs, along with a ConjunctiveGraph providing the union of contexts within a given data-store.

• Parses RDF/XML, RDFa and N3. RDF/XML and RDFa both pass all relevant W3C test cases (may be run through specs).
• Graph and ConjunctiveGraph with pluggable data-stores. MemoryStore and SQLite3Store both support contexts as well as quoted-graphs and formulae, although no appropriate graph classes yet exist.
• Graphs serialize to N-Triples and RDF/XML.
• An RDF distiller runs on this site to test out different parsers. This is also useful for running automated RDFa Test Harness. 

RdfContext is based, in part on Tom Morris' Reddy gem. See the readme on GitHub for more information. MemoryStore, SQLite3Store and ConjunctiveGraph are largely ports of Python RDFLib.

rdfa_parser gem released

I just released version 0.1.0 of the rdfa_parser_gem. This parser is written in pure Ruby and uses Nokogiri XML parsing. It passes all XHTML1 test cases and most of the existing test cases for HTML4 and HTML5.

The gem is based on previous work done by Ben Adida and some libraries borrowed from the Reddy Gem.

The project is hosted on GitHub, feel free to clone. You can try out the parser through a distiller.

Restful action caching

Caching actions without layout can be complicated when multiple request formats are used. In particular, an HTML response may use a dynamic layout, in which case you want to use the :layout => false option. However, other formats (such as XML) don't use a layout, but the :layout => false option to _caches_action_ does not properly cache the body in this case. To solve the problem, create two caches action statements:

caches_action :show,
              :if => lambda { |c| c.request.format == :html },
              :cache_path => lambda { |c| c.cache_key },
              :layout => false   caches_action :show,
              :unless => lambda{ |c| c.request.format == :html },
              :cache_path => lambda { |c| c.cache_key },
              :layout => true

Also, relying on the accept header may not cause the action caching module to detect the appropriate format. Try this in your application_controller:

before_filter :set_explicit_request_format
def set_explicit_request_format
  # Set format explicitly from accept header, unless it's already set
  request.format = :html if request.format == :any
  params[:format] ||= request.format.to_sym.to_s
end

Detecting action caching within controller

Rails offers three forms of caching within your controller: page, action and fragment. Page caching results in the fastest access times, as the results of the first call to an action are saved in a file so that subsequent accesses never even hit rails. However, for most applications, this isn't useful, as there may be dynamic content on a page, and this does not allow for authentication. Fragment caching is the most detailed, and allows different parts of a page to be cached and allows you to check for the presence of a cached fragment within your controller (or view), but it requires the most maintenance of cache keys. Action caching is a nice compromise between the two. It allows the controller to get into the action but takes care of cache key creation. It also allows for a dynamic layout using the :layout option. However, in some actions, the amount of work done by the controller may be non-trivial, so it would be nice to check for the presence of the cache within the body of the controller action. This can be solved by borrowing some code from within ActionController::Cachine::Actions.

def index
  cache_path = ActionCachePath.new(self, cache_key)
  return if self.read_fragment(cache_path.path)
  # body of action
end

Controlling your own cache keys is also useful, particularly for actions that may take a number of parameters:

def cache_key
  key = "#{params[:controller]}/#{params[:action]}"
  params.each_pair {|k, v| key += ":#{k}=#{v.gsub(/\s/, "_")}
  key
end

ButtonLabels updated for Rails 2.3

The ButtonLabels plugin described in another post has been updated for Rails 2.3.

HTTP Digest Authentication in Rails 2.3

After a fair amount of work, I'm happy to report that HTTP Digest Authentication is now a part of Rails 2.3. Although I put the finishing touches to get this into the release, it is based on work done by Dan Manges and Xavier Shay . Also, thanks to Don Parish for bug fixes and improvements after original acceptance.

Read more about HTTP Digest Authentication in Rails 2.3 Ryan's Scraps. Relevant Lighthouse entries: 1230, 1848, and 2000. The last one includes a change, not yet approved for 2.3, which allows for using the HA1 part of the digest to store a hash of the password, rather than the cleartext of the original version. Hopefully, we'll get a version of that in soon. Also, the current implementation depends on using a session secret when computing the nonce. 2000 proposes a way to avoid this so no session is required.

Hopefully. we'll see the open issues resolved and get this into a 2.3.1 update.

Gregg

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