[redland-dev] ruby bindings and typed literals

[Benno Blumenthal]

Dave Beckett wrote:

>Benno Blumenthal wrote:
>  
>
>>Hello All,
>>
>>I am interested in modifying ActiveRDF so that typed literals are
>>handled properly.
>>In the Redland Ruby bindings, there is a literal subclass of node which
>>has a lang and value properties.
>>And it is possible to define a literal node with the datatype property
>>set correctly.
>>
>>But I cannot see how to get the datatype property back out with the ruby
>>bindings.
>>
>>So what happens to numeric/date/XML literals in the ruby bindings?   Are
>>they already converted to Ruby datatypes, or am I missing something?
>>    
>>
>
>As far as I can tell, this method of the Node class does return the
>datatype URI  since it's put into hash_uri and used
>
>    # create a literal from another Node
>    def Literal.from_node(node)
>      lang = Redland.librdf_node_get_literal_value_language(node) if
>Redland.librdf_node_get_literal_value_language(node)
>      str = Redland.librdf_node_get_literal_value(node)
>      hash_uri = Redland.librdf_node_get_literal_value_datatype_uri(node)
>      hash_uri = Uri.new(Redland.librdf_uri_to_string(hash_uri)) if hash_uri
>      return Literal.new(str,lang,hash_uri)
>    end
>
>Or if this isn't what you are talking about, the above code gives you
>the fragment you need to make such a method of the base Node class:
>(hand edited, not tested)
>    def datatype(node)
>      uri = Redland.librdf_node_get_literal_value_datatype_uri(self.node)
>      uri = Uri.new(Redland.librdf_uri_to_string(uri)) if uri
>      return uri
>    end
>
>Dave
>
>  
>
Sorry for taking so long to respond -- I am on a bit of a learning 
curve.  Thank you very much, the second alternative is what I need.

Let me take it back a step (though it is essentially the same issue) -- 
how is one supposed to get the value of a literal node in the Ruby Bindings?
I managed two ways, neither of them particularly graceful or documented

                 # node is the query result for one binding
                 node = query_results.binding_value(i)

                # we determine the node type
                 if node.literal?
                     # for literal nodes we just return the value
#                     
node.to_s                                                                                            
# returns  string^^type   or string at lang or string for typed, language, 
untyped
#                                 
Redland::Literal.from_node(node.node).value          #  technique 1 
always returns string
                                  
Redland.librdf_node_get_literal_value(node.node)  # technique 2 always 
returns string


There is both a Node class and and a librdf_node class,  where the  node 
method of the Node class gets you the librdf_node object, and the 
librdf_node object has a full set of Redland methods with redland 
names.  Which is a point of confusion to me, anyway.  

Benno







-- 
Dr. M. Benno Blumenthal          benno at iri.columbia.edu
International Research Institute for climate and society
The Earth Institute at Columbia University
Lamont Campus, Palisades NY 10964-8000   (845) 680-4450