Add dublin core metadata

DC4WP.php

<?php
/*
Plugin Name: Dublin Core for WordPress
Plugin URI: http://wordpress.org/extend/plugins/dublin-core-for-wp/
Description: Inserts Dublin Core metadata (title, author, creation date, etc.) as meta tags for posts and pages. Small options screen in admin area.
Version: 0.7.2
Author: Tim McCormack, Salvatore Vassallo, Joan Junyent, Alex Oberhauser
Compatible: 2.9.2
Tags: Dublin Core, metadata

	Dublin Core Meta Tags released under the GNU General Public
	License (GPL) http://www.gnu.org/licenses/gpl.txt

	This is a WordPress plugin (http://www.wordpress.org/).
*/

/*==================*
 * Setup, if needed *
 *==================*/

/**
 * Ensure record in wp_options
 */
function dc4wp_add_options()
{
	add_option('dc4wp_rights', '', "The rights you are publishing your content under. (GPL, Copyright, CC-BY-SA, etc.)");
	add_option('dc4wp_license', '', "A URL pointing to the license terms for your content.");
}

//...and actually call it
dc4wp_add_options();


/*========================*
 * Generate HTML metadata *
 *========================*/

/**
 * Write a meta tag if the content is non-empty.
 */
function dc4wp_writeMetaTag($name, $content, $scheme = "")
{
	if($scheme)
	{
		$scheme = "scheme=\"{$scheme}\" ";
	}
	if($content)
	{
		echo "\n\t\t<meta name=\"{$name}\" content=\"{$content}\" {$scheme}/>";
	}
}

/**
 * Gather and output the Dublin Core metadata.
 */
function dc4wp_write_html_metadata()
{
	global $wp_query, $post, $wpdb;

	/* It only makes sense to put metadata in single articles. */
	if((is_single() || is_page()) && have_posts())
	{
		$wp_query->the_post();//load the $post variable
		
		$post_cats = get_the_category();
		$def_cat = get_option('default_category');//we want to ignore this one
		$DC_subjects = array();
		foreach($post_cats as $one_cat)
		{
			if($one_cat->cat_ID != $def_cat)//prevent "Uncategorized" from appearing
			{
				$DC_subjects[] = $one_cat->cat_name;
			}
		}
		$post_tags = get_the_tags();
		if($post_tags) { // sometimes array(), sometimes false for pages...
			foreach($post_tags as $one_tag) {
				$DC_subjects[] = $one_tag->name;
			}
		}
		
		$DC_title = the_title('', '', false);
		
		$auth_first = get_the_author_meta('first_name');
		$auth_last = get_the_author_meta('last_name');
		$auth_nick = get_the_author_meta('display_name');
		if(empty($auth_first) or empty($auth_last)) {
			$DC_creator_name = $auth_nick;
		} else {
			$DC_creator_name = "$auth_last, $auth_first";
		}

		$DC_identifier = get_permalink();
		$DC_date_created = get_the_time('Y-m-d\TH:i:s'); /* http://www.w3.org/TR/NOTE-datetime */

		$DC_publisher = get_settings('blogname');
		$DC_publisher_url = get_settings('home');

		$DC_language = get_bloginfo('language');	
			
//		$DC_description = get_bloginfo('description');
//		<meta name="DC.description" content="{$DC_description}" />
		
		$DC_license = get_option('dc4wp_license');

		$wp_query->rewind_posts();//reset so the loop doesn't freak out later on

echo <<<EOHTML
		<meta name="DC.publisher" content="{$DC_publisher}" />
		<meta name="DC.publisher.url" content="{$DC_publisher_url}/" />
		<meta name="DC.title" content="{$DC_title}" />
		<meta name="DC.identifier" content="{$DC_identifier}" />
		<meta name="DC.date.created" scheme="WTN8601" content="{$DC_date_created}" />
		<meta name="DC.created" scheme="WTN8601" content="{$DC_date_created}" />
		<meta name="DC.date" scheme="WTN8601" content="{$DC_date_created}" />
		<meta name="DC.creator.name" content="{$DC_creator_name}" />
		<meta name="DC.creator" content="{$DC_creator_name}" />
		<meta name="DC.rights.rightsHolder" content="{$auth_nick}" />		
EOHTML;
		dc4wp_writeMetaTag('DC.language', $DC_language, 'rfc1766');
		foreach($DC_subjects as $oneSub) {
			dc4wp_writeMetaTag('DC.subject', $oneSub);
		}
		dc4wp_writeMetaTag('DC.rights.license', $DC_license);
		dc4wp_writeMetaTag('DC.license', $DC_license);
		echo "\n";//make source more readable
	}
}

//Hook to print metadata
add_action('wp_head', 'dc4wp_write_html_metadata');


/*==========================*
 * Administration interface *
 *==========================*/

/**
 * Display options page.
 */
function dc4wp_options_page()
{
	global $wpdb;
	$updated = false;
	// Start updating
	if(isset($_POST['Submit']))
	{
		// updating license (dc.rights.license)
		$DC_license = $_POST['dc4wp_license'];
		update_option('dc4wp_license', $DC_license);
		$updated = true;
	} 		 
	$DC_license = get_option('dc4wp_license');
	if($updated)
	{
		echo <<<EOHTML
			<div class="updated">
				<p>Options saved.</p>
			</div>
EOHTML;
	}
	echo <<<EOHTML
		<div class="wrap">
			<h2>Dublin Core for Wordpress Settings</h2>
			<form method="post" action="{$_SERVER['REQUEST_URI']}">
				<fieldset class="options">      	
					<legend>Add metadata dublincore</legend>      	
					
					<label for="">License:</label>
					<input type="text" size="45" name="dc4wp_license" value="{$DC_license}" title="The URL of the license of publish under." />
					
					<p>Examples:</p>
					<ul>
						<li><a href="http://creativecommons.org/licenses/by-sa/2.5/" target="_blank">http://creativecommons.org/licenses/by-sa/2.5/</a></li>
						<li><a href="http://www.gnu.org/licenses/gpl.html" target="_blank">http://www.gnu.org/licenses/gpl.html</a></li>
						<li>Empty for no license metadata</li>
				</fieldset>
				<input type="submit" name="Submit" value="Update Options" />
			</form>
		</div>
EOHTML;
}

/**
 * Register the options page.
 */
function dc4wp_admin_menu()
{
	//title of page, name of option in menu bar, which function lays out the html
	add_options_page(__('DC4WP Options'), __('DC4WP'), 5, basename(__FILE__), 'dc4wp_options_page');
}

//Hook for option apge registration
add_action('admin_menu', 'dc4wp_admin_menu');

?>

Should update this plugin to draw on the fields we privilege in COinS--fields like "real_author_first," and so on. See the list here: https://gist.github.com/2628506 . What else do we need to add? What in RDF is not DC? It would make most sense to combine the COinS and the DC, but my skill level has pretty much already been exhausted!

Some combinations will be tricky to impossible. For example, DC doesn't distinguish first or last names. There might also be a sneaky maneuver required in sorting out the affiliation -- I take it that that will refer to the author's affiliation, which means that the referent is different from the other data on the page. That is, author, volume, etc. info is all referring to the article on the page. affiliation isn't, so it'll be tricky to parse that out and/or represent it in the page.

Good luck!