View source for Metadata Retriever Plugins

{{DiscoverEd Specification
|contact=Nathan Yergler
|project=AgShare, FSKN
|status=Complete
}}

DEd sites may wish to include metadata about Resources from other sources, including web services (ie, Semantic Analysis), databases, etc.  This describes a plugin system for adding sources of information at aggregation time.

== Requirements ==

Metadata retriever plugins are [http://wiki.apache.org/nutch/PluginCentral Nutch plugins] which implement the <code>MetadataRetriever</code> extension point.  MetadataRetriever extensions must implement a single method, <code>retrieve</code>.  <code>retrieve</code> takes a Resource as an argument, and may add additional metadata to it.  <code>retrieve</code> is not responsible for persisting the Resource.

We will implement two demonstration plugins: a "dummy" plugin which logs the URLs being passed to it, and a functional demonstration which uses the Delicious API to [http://delicious.com/help/api#posts_suggest retrieve suggested and popular tags] for a page. 

== Implementation ==

* Added support for storing arbitrary metadata on Resource objects 
* Added support to TripleStore for serialization an de-serialization
* Implemented the org.creativecommons.learn.plugin.MetadataRetriever extension point and org.creativecommons.learn.plugin.MetadataRetrievers extension loader
* Implemented test plugins

==Deferred until later==

* Configuration parameters for plugins (the Delicious plugin reads from discovered.xml, but the plugin.xml manifest doesn't state that it needs parameters).
* Allow sequencing of MetadataRetriever plugins, to determine which are authoritative