...

 <% if (extraHeadData != null)
    { %>
    <%= extraHeadData %>
 <% } %>

If you have heavily customized your metadata fields away from Dublin Core, you can modify the crosswalk that generates these elements by modifying {{\[dspace\]/config/crosswalks/xhtml-head-item.properties}}.

...

In general, OAI-PMH isn't useful to Search Engines

Feel free to support OAI-PMH, but be aware that in general it is not useful for search engines:

• No reliable way to determine OAI-PMH base URL for a DSpace site.
• No standard or predictable way to get to item display page or full text from an OAI-PMH record, making effective indexing and presenting meaningful results difficult.
• In most cases provides only access to simple Dublin Core, a subset of available metadata.

• NOTE: Back in 2008, Google officially announced they were retiring support for OAI-PMH based Sitemaps. So, OAI-PMH will no longer help you get better indexing through Google. Instead, you should be using the DSpace 'generate-sitemaps' feature described above.

Other methods

See: http://wiki.lib.sun.ac.za/index.php/SUNScholar/Web_Analytics