Geonetwork uses for her search function Lucene. Lucene can be used directly or via Hibernate Search. 


'''Option 1'''
Implementing the search with Hibernate Search above Lucene. 
Advantages:
 * Using HQL for defining searches. Because we use Hibernate already, HQL is used anyway.  
 * Hibernate Search is using Apache Lucene(tm) internally, and always provides the ability to fallback to the native Lucene APIs.


'''Option 2'''
Implementing the search with Lucene directly. 
 * No abstraction to Lucene. Same approach used as in the Geonetwork Legacy.