Re: Enumerating RDF::Format

On 13/05/2012 21:12, "Gregg Kellogg" <gregg@greggkellogg.net> wrote:
> Hi Nick!
> 
> On May 13, 2012, at 4:33 AM, Nicholas Humfrey wrote:
> 
>> Hello,
>> 
>> I have been using RDF.rb gem as part of dbpedialite.org for a couple of
>> years now. I opened an issue about enumerating the registered list of
>> RDF::Formats:
>> 
>> https://github.com/bendiken/rdf/issues/16
> 
> Sorry, I wasn't aware of the outstanding issue. As you probably know, the
> active gem is maintained on my fork (http://github.com/gkellogg/rdf), and Arto
> hasn't been too responsive at keeping in sync.
> 
>> Time has passed and this still isn't possible, so I thought I would try and
>> come up with a patch. Specifically, I want iterate through the registered
>> list of formats and get:
>> 
>> * The format name (eg 'RDF/XML' or 'N-Triples')
>> * The default (most official) content type (eg 'text/turtle')
>> * The default file suffix (eg .rdf or .trix)
> 
> I do something like this in my RDF Distiller
> (http://rdf.greggkellogg.net/distiller), where I need to present possible
> input and output formats using basically the following:
> 
>     RDF::Format.each.to_a.map(&:reader).compact.map(&:to_sym)
> 
> When loaded up with the linked data gem, this generates the following:
> 
>     [:ntriples, :nquads, :jsonld, :json, :microdata, :n3, :n3, :rdfa, :rdfa,
> :rdfa, :rdfa, :rdfa, :rdfxml, :trig, :trix, :turtle, :turtle]
> 
> You can do the same thing with &:writer to get the list of available writers:
> 
>     [:ntriples, :nquads, :jsonld, :json, :n3, :n3, :rdfa, :rdfa, :rdfa, :rdfa,
> :rdfa, :rdfxml, :trig, :trix, :turtle, :turtle]
> 
> (basically, the same, but without a microdata writer).
> 
> In the case of the Distiller, it uses either content-negotiation, or file
> extension to figure out the appropriate format to use. The sinatra-linkeddata
> gem can do this for you, or the sparql gem if you want to have a SPARQL
> endpoint too:
> 
>     require 'sinatra-respond_to'
>     require 'sinatra-linkeddata'
> 
>     register Sinatra::RespondTo
>     register Sinatra::LinkedData
> 
> This will then respond based on either the Accept header or the file extension
> and format the RDF::Queryable results using the appropriate writer.
> 
> Check out http://github.com/gkellogg/rdf-distiller and
> http://github.com/gkellogg/github-lod for some examples of doing this.
> 
>> This is used to generate a <link rel="alternate"> and hyperlinks to other
>> formats in the HTML page.
> 
> You could do this with a variation of the previous Format.each clause:
> 
>     RDF::Format.file_extensions.keys
> 
> This will give you the file extensions of all loaded formats, which RespondTo
> should dispatch on.
> 
> Also, note that the RDF::Reader.open() will look at various things, including
> content type, file extension, specified format, and if necessary, content
> sniffing to try to find an appropriate reader. It's pretty good, but could be
> improved upon further, particularly for HTML serializations.
> 
>> Unfortunately the internal data structures currently make this difficult and
>> there is no name for a format stored (other than deriving it from the class
>> name). For the time being I have decided to resort to storing it in my own
>> data structure:
>> http://github.com/njh/dbpedialite/blob/master/lib/formats.rb
> 
> Yes, the internal structures don't make this easy. I'd certainly entertain a
> reasonable patch that made this easier. Perhaps just exposing the code I show
> here as RDF::Format class methods would be useful.

Hi Gregg!

Thanks for the very helpful email. I will take a look at making a patch - it
did try some similar things to what you have suggested but it felt quite
hacky and I got some weird results - such as Turtle appearing multiple
times.

Do you think it would make sense to add a new 'name' property to formats? I
would really like to be able to display 'RDF/XML' in the list of alternative
formats. I find it a bit weird that specific formats aren't more like
instances of the class RDF::Format.

Perhaps your fork should become the official repo for the gem? Lots of gems
have done that now...


nick.


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Received on Sunday, 13 May 2012 21:57:46 UTC