Don't expand paths relative to __FILE__ in metadata and reader.

lib/rdf/tabular/metadata.rb

@@ -142,14 +142,9 @@ def self.open(path, **options)
           'Accept' => 'application/ld+json, application/json'
         }
       )
-      if RDF::URI(path).relative?
-        path = if Gem.win_platform?
-          # Expanded path starts with drive letter
-          "file:/" + File.expand_path(path, __FILE__)
-        else
-          "file:#{File.expand_path(path, __FILE__)}"
-        end
-      end
+
+      # Resolve relative paths to use the file scheme, bearing in mind that Windows expanded paths always start with a drive letter, not a slash.
+      path = (Gem.win_platform? ? "file:/" : "file:") + File.expand_path(path) if RDF::URI(path).relative?
       RDF::Util::File.open_file(path, **options) do |file|
         self.new(file, **options.merge(base: path, filenames: path))
       end

lib/rdf/tabular/reader.rb

@@ -80,12 +80,7 @@ def initialize(input = $stdin, **options, &block)
         @options[:base] ||= input.path if input.respond_to?(:path)
         @options[:base] ||= input.filename if input.respond_to?(:filename)
         if RDF::URI(@options[:base]).relative? && File.exist?(@options[:base].to_s)
-          file_uri = if Gem.win_platform?
-            # Expanded path starts with drive letter
-            "file:/" + File.expand_path(@options[:base], __FILE__)
-          else
-            "file:" + File.expand_path(@options[:base], __FILE__)
-          end
+          file_uri = (Gem.win_platform? ? "file:/" : "file:") + @options[:base]
           @options[:base] = RDF::URI(file_uri.to_s).normalize
         end