publications_controller.rb

class PublicationsController < ActionController::Base
  def show
    @publication = Publication.find params[:id]

    # If you need a specific version, get that from the URL.
    version_id = ...
    @publication = @publication.versions.find version_id

    keywords = []  # the keywords belonging to @publication at the time
    keywords_versions = Version.all :item_type => 'Keyword', :publication_id => @publication.id

    keywords_versions.group_by(&:item_id).each do |item_id, versions|
      v = versions.first :conditions => ['created_at > ?', (@publication.created_at - 3.seconds)]
      keywords << (v ? v.reify : Keyword.find(item_id))
    end

    @variables = keywords.map do |keyword|
      variable = keyword.variable
      # Handle situation where variable has since been destroyed
      unless variable
        variable = Version.last(:item_type => 'Variable', :item_id => keyword.variable_id).reify
      end
      variable
    end

  end
end

show.html.erb

<h1><%= @publication.name %></h1>

<h2>Variables</h2>

<% variables.each do |variable| %>
  <%= variable.name %><br>
<% end %>