More flexible and consequent filter APIs

[white-gecko]

This issue contradicts the solution proposed in #114 and #109 .

sparql_query:

• behavior on master is: page.rdf | sparql_query: <query>
• behavior on develop is: <query> | sparql_query (page.rdf is taken from the Jekyll::RdfHelper)
• behavior should be: [<rdf_resource>] | sparql_query: <query>
  • shortcut for page.rdf | sparql_query: <query> is sparql_query: <query> (page.rdf is taken from the Jekyll::RdfHelper)
  • "http://resource/" | rdf_get | sparql_query: <query> would also be possible
  • in all cases the variable ?resourceUri in the query is replaced/bound by the given resource (input)

rdf_property:

• behavior on master and develop is: <resource> | rdf_property: <property>
• behavior should be: <resource> | rdf_property: <property>
  • shortcut for page.rdf | rdf_property: <property> is rdf_property: <property> (page.rdf is taken from the Jekyll::RdfHelper)
  • "http://resource/" | rdf_get | rdf_property: <query> would also be possible (as it is now)

same for rdf_inverse_property

[Simaris]

Unfortunately, {{ |rdf_property: property }} or {{ rdf_property: property }} are not valid expressions to jekylls liquid engine, so these short-cuts are not possible. The closest we can realise (as far as I know) is {{ nil | rdf_property: property }}.

[white-gecko]

I think if this is not possible we don't need these shortcut options. Using nil might be confusing. I think the only simplification would be to allow {{ page | rdf_property: property }} as well as {{ page.rdf | rdf_property: property }}.