This post originated from an RSS feed registered with Java Buzz by Michael Cote. Original Post: Namespace URI Lookup in Ruby Feed Title: Cote's Weblog: Coding, Austin, etc. Feed URL: https://cote.io/feed/ Feed Description: Using Java to get to the ideal state. Latest Java Buzz Posts Latest Java Buzz Posts by Michael Cote Latest Posts From Cote's Weblog: Coding, Austin, etc.

I've been slowing learning Ruby over the past month or so. Tonight I was playing around with using REXML to parse out RSS feeds, and I started getting concerned about getting the correct prefix for namespace'ed elements -- like the dublin core crap.

As far as I know, you can't gurantee that the prefixes used will be the same. So, you can reliably get dublin core dates with something like element.each("//dc:dates"). The dc part might change document per document.

So, I was looking for a way in XPath or Ruby (REXML, I guess) to figure out the correct XPath to use. I didn't find much (though this seemed to indicate how you'd use XPath, but it didn't seem to work for me), so I tried my dumb-hand at writing some actual Ruby code to create a hash of namespace URI's to their prefixes:

    require 'rexml/document'

    xmlresp = File.open("bushwald.rss")
    xml = REXML::Document.new(xmlresp)
    defaultNS = xml.root.namespace('')

    ns = xml.root.namespaces
    prefixes = xml.root.prefixes

    # remove the default, so lists 
    # are equal
    ns.delete(defaultNS)
    nsHash = {defaultNS => ''}
    ns.each_index{|i|
        uri = ns[i] 
        prefix = prefixes[i]
        nsHash[uri] = prefix
        #puts uri+" = "+prefix
    }

    #print it out
    nsHash.each{|key, value|
     puts key+" = "+value
    }

Which, in the case of my del.icio.us feed, outputs this:

mcote-laptop:~/dev/ruby-playgrond cote$ ruby ns-hash.rb
http://www.w3.org/1999/02/22-rdf-syntax-ns# = rdf
http://purl.org/rss/1.0/ = 
http://purl.org/rss/1.0/modules/taxonomy/ = taxo
http://purl.org/dc/elements/1.1/ = dc
http://purl.org/rss/1.0/modules/syndication/ = syn
http://webns.net/mvcb/ = admin

I really have no idea if that's anything, but it sure is fun typing up and running Ruby.